CBC British Columbia
Questions for Claire


Friday, March 5, 2010 | 10:35 AM PT

I want to take the opportunity to thank everyone that has taken the time to ask such interesting questions over the past couple of years, many of which really got my brain working! I have had the chance to tackle a huge range of subjects with a meteorological slant - I've researched continued threat of the pine beetle to our forests under a changing climate; how an artist can incorporate scientifically correct visual references of the weather in B.C.; what the weather is like on Mars and (my favourite) why a young brothers top bunk bed was always warmer than the bottom bunk bed!

This will be the last entry to this blog - and I wanted to thank you all for taking part.

Cheers for now!

Claire Martin

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What is the chance of Vancouver seeing a white Christmas this year?

Tuesday, December 1, 2009 | 03:08 PM PT

Question submitted by Penny
(Burnaby, BC)

Hi there Penny,

Yes my thoughts too turn to Christmas as soon as the calendar hits December!

Environment Canada has a great web sit dedicated to this answer at http://www.msc-smc.ec.gc.ca/media/xmas/index_e.html.

Basically we here in the Lower Mainland stand around an 11% chance.. which is not great, but remember last year - we got dumped on with 22 cm on the 21st and then 27 cm on the 24th and finally got another 16 cm on the 26th! So we can only hope for a repeat performance.

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Is the recent typhoon activity in the Western Pacific unusual or not?

Thursday, October 22, 2009 | 06:17 PM PT

Question submitted by Ross McKinnon
(Hainan, China)

First off - let me copy the entire e-mail that I got from Ross:
"I live on the Island of Hainan in the South China Sea, and have been here for the past seven years from my former home on Pender Is. BC. We are now just waiting for our 6th typhoon of the year, all in the past 8 weeks. This is 6 more than has ever occurred here before, so what is going on?"

Great question! Here's what I have discovered:

To date we have seen eight tropical cyclone, five of which became typhoons, two reaching Super Typhoon status, the strongest classification of tropical cyclones in the Western Pacific. But when we look at the numbers, 2009 has actually been slightly below average. So far we have seen 19 tropical storms in the Western Pacific, which is slightly behind the pace needed to reach the yearly average of 27. Despite the fact that 2009 has been below average for the season, the past month has been remarkable, with five of the eight storms making direct landfall in Asia.

What is behind this recent uptick in activity and why are all the storms seemingly coming at once, and late in the season?

The answer may be El Nino, which refers to a periodic change in the atmosphere and ocean in the Pacific. During El Nino, the waters in the central and eastern Pacific are warmer than normal, and the effects on global weather can be drastic and far-reaching.

According to forecasters in China, we see more cyclones later in the season during El Nino years in the Western Pacific, and they tend to form farther east. With the warmer sea surface temperatures during an El Nino event, this would allow these storms more time over open water to grow into large and powerful typhoons. In fact, we tend to see more "Super Typhoons" during El Nino years, and this is true again this year, as Choi-Wan and Melor both reached Super Typhoon status.

El Nino also is a likely culprit for the inactivity in the North Atlantic, since El Nino can cause more wind shear in the upper atmosphere, a condition that limits the ability of Tropical Cyclones to survive.

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I have a painting commission in the works and I'd like to include a visual reference to diagrams of weather patterns related to the Vancouver region. Are there such visuals available online?

Thursday, October 8, 2009 | 01:25 PM PT

Question submitted by Janice
(Vancouver, BC)

Wow, first off - congratulations Janice.

Next visual representations of weather maps around Vancouver (all of Canada in fact) are available on line. The best place to go is the Environment Canada web site at http://www.weatheroffice.gc.ca/jet_stream/index_e.html.

Also to get good quality representations of cold fronts, warm fronts etc check out http://ww2010.atmos.uiuc.edu/(Gh)/guides/mtr/home.rxml

Note that there is one meteorological feature that is primarily only used on Canadian maps: a trowal, or a trough of warm air aloft (American's call it a warm occlusion).

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What does dewpoint mean in the weather forecast? And what is the "DEW Line"??

Thursday, October 8, 2009 | 01:18 PM PT

Question submitted by Sharyn Pountney
(West Vancouver, BC)

Sharyn, the dew point is the temperature to which a given parcel of air must be cooled, at constant barometric pressure, for water vapor to condense into water. The condensed water is called dew. The dew point is a saturation point. When the dew point temperature falls below freezing it is often called the frost point, as the water vapor no longer creates dew but instead creates frost or hoarfrost by deposition.

The dew point is associated with relative humidity. A high relative humidity indicates that the dew point is closer to the current air temperature. Relative humidity of 100% indicates the dew point is equal to the current temperature and the air is maximally saturated with water. When the dew point remains constant and temperature increases, relative humidity will decrease.

The dew point really won't be mentioned much in a forecast, but you may here the odd broadcaster mentioning the reading during their weather presentation, as an indication of how close a site may be to becoming saturated or "fogged in".

And in regards to the "DEW line": The Distant Early Warning Line, also known as the DEW Line or Early Warning Line, was a system of radar stations in the far northern Arctic region of Canada. I was lucky enough to work on the DEW line before it was essentially disbanded in the late 1990's.

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Do you have an opinion yet, as to whether El Nino,or his evil sibling La Nina will prevail this coming winter (09-10) and what the consequences will be in either case?

Thursday, October 8, 2009 | 01:08 PM PT

Question submitted by Gregg
(Vancouver, BC)

Ah, El Niño! Gotta love this little guy!

First off, a definition: El Niño is the periodic warming of central and eastern tropical Pacific waters, which usually occurs on average every two to five years and typically lasts about 12 months.

And yes, most scientists now expect this El Niño event to continue developing during through the next several months, with further strengthening possible. So essentially the event is expected to last through winter 2009-10.

There's an excellent article on this at http://www.noaanews.noaa.gov/stories2009/20090709_elnino.html.

The big issue for us here on the west coast, with these events, is the change in the precipitation patterns - namely our snowfall patterns. Unfortunately there is very little concise evidence to show that we historically see either more or less snow during an El Niño event.

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Is the weather different around urban cities, or centres? If so why?

Wednesday, September 30, 2009 | 09:33 AM PT

Question submitted by Curtis Bennett
(Kelowna, BC)

This is a great question Curtis, and the answer is "absolutely"! The effect is known as the Urban Heat Island (UHI) effect.

An urban heat island (UHI) is a metropolitan area which is significantly warmer than its surrounding rural areas.
The observed temperature difference is larger at night than during the day, and is most apparent when winds are weak. Seasonally, UHI is seen during both summer and winter. The main cause of the urban heat island is modification of the land surface by urban development which uses materials which effectively retain heat; waste heat generated by energy usage is a secondary contributor. As population centers grow they tend to modify a greater and greater area of land and have a corresponding increase in average temperature.

Monthly rainfall is greater downwind of cities, partially due to the UHI. Increases in heat within urban centers increases the length of growing seasons, and is even thought to potentially decrease the occurrence of weak tornadoes (more research is needed for thorough confirmation). Increases in the death rate during heat waves has been shown to increase by latitude due to the urban heat island effect. The UHI decreases air quality by increasing the production of pollutants such as ozone, and decreases water quality as warmer waters flow into area streams, which stresses their ecosystems.

Not all cities have a distinct urban heat island, however. Mitigation of the urban heat island effect can be accomplished through the use of green roofs and the use of lighter-colored surfaces in urban areas, which reflect more sunlight and absorb less heat. Despite concerns raised about its possible contribution to global warming, any impact of the urban heat island on global warming is uncertain, its impact on climate change has not been proved observationally or by any quantitative modelling, though recent qualitative speculations indicate that urban thermal plumes may contribute to variation in wind patterns that may itself influence the melting of arctic ice packs and thereby the cycle of ocean current.

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Are dust storms in Australia really that unusual? Is this another sign of climate change?

Wednesday, September 23, 2009 | 01:25 PM PT

Question submitted by Mi-Young
(Williams Lake, BC)

Good question Mi-Young! Simply put the answer to both questions is "no"!

The Australian Bureau of Meteorology has a great discussion on the web on this subject at http://www.bom.gov.au/lam/climate/levelthree/c20thc/storm8.htm

Dust-storms are for the most part restricted to the drier inland areas of Australia, but occasionally, during widespread drought, they can affect coastal districts. The figure below shows the average distribution of dust-storms over Australia. One of the most spectacular examples was the storm that swept across Melbourne in February 1983, late in the severe El Niño drought of 1982/83. The extended dry period of the 1930s and 1940s generated many severe dust-storms, culminating in the summer of 1944/45 when on several occasions dust in Adelaide was so thick that street lighting had to be turned on. But uncomfortable as dust-storms may be for town and city dwellers, by far their worst effect is the stripping of topsoil from Australia's arable land.

Remember also that any one single event, as far as the daily weather is concerned, is never an indicator of "global climate change". Climate change will occur on a far greater scale. However a series of single events, that appear to become "the new normal" is most definitely an indicator that our weather patterns, and hence climate, is changing.

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Why is the equinox date not the same each year?

Monday, September 21, 2009 | 01:14 PM PT

Question submitted by Mike
(Salmo, BC)

While the September equinox occurs on September 22 in 2008 and 2009, it occurs on September 23 in 2010 and 2011 (UTC). The September equinox has also occurred on September 24(UTC), with the last occurrence on that date being 1931. The next time a September 24 equinox occurs will be in the year 2303. Moreover, a September 21 equinox will occur in 2092.

There are a few explanations on why the equinox dates differ in the Gregorian calendar. The varying dates of the equinox are mainly due to the calendar system – most western countries use the Gregorian calendar, which has 365 days in a year, or 366 days in a leap year. According to the National Maritime Museum, the equinoxes generally occur about six hours later each year, with a jump of a day (backwards) on leap years. An extra day is added in a leap year to minimize a gradual drift of the equinox date through the seasons.

As for the tropical year, it is approximately 365.242199 days, but varies from year to year because of the influence of other planets. A tropical year is the length of time that the sun takes to return to the same position in the cycle of seasons, as seen from earth. The exact orbital and daily rotational motion of the Earth, such as the “wobble” in the earth's axis (precession), also contributes to the changing solstice dates.

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What is a meteorologist? What exactly do they (you) do?

Monday, September 14, 2009 | 10:44 AM PT

Question submitted by David
(Terrace, BC)

I get this question a lot, David, so I thought I would answer it here!
While many people know a meteorologist is a person experienced and trained in meteorology or an atmospheric science, many viewers still want to know several questions about meteorologists.

What Does a Meteorologist Do?
What Are the Types of Meteorologists?
How Can I Become a Meteorologist?

A meteorologist is a term often used to describe anyone who studies meteorology. Popularly, any weather reporter on television is often called a meteorologist, but that is not always the case. In 1990, the American Meteorological Society set an official description of a meteorologist.

A meteorologist is an individual with specialized education who uses scientific principles to explain, understand, observe or forecast the earth's atmospheric phenomena and/or how the atmosphere affects the earth and life on the planet. This specialized education would be a bachelor's or higher degree in meteorology or an atmospheric science. Individuals who have little formal education in the atmospheric sciences, or who have taken only industry survey courses, and who disseminate weather information and forecasts prepared by others, are properly designated weathercasters.

Furthermore there are many types of meteorologists:
Meteorologists work in a range of fields each with a specialized area of study. Essentially, a meteorologist is a specialized scientist that focuses on some aspect of the atmosphere. The following list shows just some of the types of meteorologists.
Broadcast Meteorologists: These folks are the people who interpret and report the weather for television.
Research Meteorologists: Many of these scientists work for the National Weather Service or other government agency. NASA, the Environmental Protection Agency, and the military. Most have a particular issue they are studying.
Teachers and Professors: Many people use their knowledge of the atmosphere and meteorology to become educators. Sharing your knowledge at a high school or college level can help to create future generations of meteorologists.
Forensic Meteorologists: This type of meteorologist will often investigate claims for insurance companies on past weather or research weather for a court of law.
Consulting Meteorologists: Large companies now hire meteorologists for consultation work. Companies such as Liz Claiborne, M&M Candies, and Target all hire meteorologists to improve their buying and selling power.
Climate Meteorologists: This type of meteorologist looks at long-term weather patterns and data to help predict future climate trends and past climate data.
Archive Meteorologists: Many weather scientists will also be in charge of researching, verifying, and reporting on storms of the past.

It's a fun and fascinating science, and I love working in this field.

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Is there such a thing as "cold lightning"? I have heard there is a relatively harmless form of lightning - is this it?

Thursday, August 13, 2009 | 09:43 AM PT

Question submitted by Patricia Lewis
(Vancouver, BC)

Patricia - in light of the sad story that has come out of Ontario - I thought I would address this question on my blog.

Let me be very clear here:

Lightning is an atmospheric discharge of electricty - but on a very large, very dangerous, potentially deadly scale. In the atmosphere an electrical discharge, a leader of a bolt of lightning, can travel at speeds of 60,000 m/s (130,000 mph), and can reach temperatures approaching 25,000 °C (54,000 °F), hotter than the surface of the sun and hot enough to fuse silica sand into glass channels.

90% of most cloud-to-ground strikes are considered "negative". The term negative is used to describe the polarity of the cloud base at the time of the strike. The only descriptive difference between the two kinds of lightning then (positive and negative) is the reversal of polarities in the cloud base. Normally the negative charge collects in the cloud base, with a corresponding net positive charge in the ground under the cloud. Lightning strikes originating from this configuration are therefore considered "negative" strikes.

An average bolt of negative lightning (the most common type of lightning) carries an electric current of 30 kiloamperes (kA), and transfers a charge of five coulombs and 500 MJ of energy. Large bolts of lightning can carry up to 120 kA and 350 coulombs.

An average bolt of "positive" lightning carries an electric current of 300 kA or about 10 times that of negative lightning.

Positive lightning, also known colloquially as "bolts from the blue", make up less than 5% of all lightning. They occur when the leader forms at the positively charged cloud tops, with the consequence that a negatively charged streamer issues from the ground. The overall effect is a discharge of positive charges to the ground. Research carried out after the discovery of positive lightning in the 1970s showed that positive lightning bolts are typically six to ten times more powerful than negative bolts, last around ten times longer, and can strike tens of kilometres/miles from the cloud. At the time of writing this, it is thought that the people struck in Ontario on August 12th were indeed hit by a positive lightning bolt.

Remember to always take cover INDOORS during a thunderstorm. Never hide under a tree, and as long as you can hear thunder, the threat of a lightning stike close by remains.

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How can you forecast with such accuracy the onset of a meteor shower? Last night was spectacular!

Wednesday, August 12, 2009 | 09:22 AM PT

Question submitted by Robert
(100 Mile House, BC)

Thanks for the question Robert. I have heard a lot of similar questions recently in light of the Perseidian meteor shower we have just encountered.

You have to remember that astronomical events are beyond the atmosphere of the earth and hence happen in wide open outer space, and as such are calculable timed events and can be "forecast" with perfect accuracy. The Perseid meteor shower has in fact been observed for about 2000 years, with the earliest information on this meteor shower coming from the Far East. The cloud of dust that we (the Earth) pass through consists of particles ejected by the comet Swift-Tuttle as it travels on its 130-year orbit.

The shower is visible from mid-July each year, with the peak in activity being between August 9 and 14, depending on the particular location of the stream. During the peak, the rate of meteors reaches 60 or more per hour. They can be seen all across the sky, but because of the path of Swift-Tuttle's orbit, Perseids are primarily visible in the northern hemisphere. As with all meteor showers, the rate is greatest in the pre-dawn hours, since the side of the Earth nearest to turning into the sun scoops up more meteors as the Earth moves through space.

For more on astronomically related weather events check out spaceweather.com

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With our recent fires, I have heard a great deal about a weather condition called "crossover", when the humidity is lower than the temp. Can you explain what this means, and what it does during fire season?

Friday, July 31, 2009 | 09:44 AM PT

Question submitted by Lisa Nagy
(Kelowna, BC)

Lisa! This is the first time I have ever been truly stumped by a question!! Congratulations.

I went to the BC Wildfire Management Branch, Ministry of Forests and Range, and got some help from a couple of great people there.

Here's what they had to say: "The formal definition of Crossover as listed by CFFC (Canadian Forest
Fire Centre) is "the point at which the numerical value of the ambient relative humidity is less than, or equal to, the numerical value of the ambient air temperature". This may be used as a rule of thumb indicator of extreme burning conditions. It is a rule of thumb indicator primarily used by fire suppression staff but there are some limitations to it being used as a definitve law."

So there you go! And thanks for the challenging question.. I now know more about fire weather forecasting too!

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As the earth spins one rotation per day, does it spin the weather patterns? For example does England eventually get our "weather" and do we get China's?

Wednesday, July 29, 2009 | 12:00 PM PT

Question submitted by David Mallory
(Vancouver, BC)

Fantastic question! But I have to go back to basics to explain this:
Weather is created due to the day by unequal heating of the atmosphere, and the motion of the earth spin, drags the atmosphere around with it, with the overall result being a combination of global patterns of wind which follow a regular yearly cycle.

Wind and weather are created by the action of the Sun, heating up different parts of the land and sea by varying amounts. For example, the sun is overhead in the tropics, therefore it has less atmosphere to pass through so the effects of heat are greater. Warm air rises and cooler air flows alongside, replacing the displaced air resulting in large scale air movement or wind as we know it.

The rotation of the earth means that it is a spinning globe where at one point of the equator is traveling at 1100 km/hour, whilst a point at the poles is not affected by rotation. This results in what is known as Coriolis forces which act to cause an apparent deflection of a motion. This can be explained in terms of an imaginary force that can be translated into terms of gravitational pressures.

Due to the effects of the Sun and the effect of varying degree of heat on certain areas such as the equator and the Poles, resulting in surface winds or air moving towards the equator at the surface and towards the Poles at altitude. "At mid-latitudes we can see that air moves towards the Poles via the surface and moves to the Equator at altitude".

The effects of wind force and direction dictates to some extent to the type of weather we are going to experience, and how that weather will affect people "along the way".

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What exactly is humidex? How come sometimes you mention it, and sometimes you don't?

Tuesday, July 28, 2009 | 01:57 PM PT

Question submitted by Phyllis Gee
(Burnaby, BC)

The humidex is an index (a computed value as opposed to something measured) devised to describe how hot or humid weather feels to the average person. The humidex combines the temperature and humidity into one number to reflect the perceived temperature. It takes into account these two important factors that affect summer comfort. It is therefore a better measure of how stifling the air feels than either temperature or humidity alone. A humidex of 40 with, for example, a temperature of 30 degrees means that the sensation of heat when it is 30 degrees and the air is humid is more or less the same as when it is 40 degrees and the air is dry. We must be careful not to depend on this interpretation alone: it is a mere indication of physiological reactions, not an absolute measure.

The humidex is particularly significant when its value is greater than 30. We only display humidex values of 25 or higher for a location which reports a dew point temperature above zero (0°C) and an air temperature of 20°C or more. Below this value, the humidex is too close to the air temperature to be considered significant.

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It is suddenly hot and humid here in Vancouver, how unusual is this? Will records fall?

Tuesday, July 28, 2009 | 01:51 PM PT

Question submitted by Tim Allen
(Vancouver, BC)

Hi there Tim,
Vancouver does not normally get this hot and humid! As I write this (12 noon on July 28th) we're 28 deg C, with a humidex of 34. Abbotsford is 32 deg C, with a humidex of 40.
Our all time record hot temperature was set back in August of 1960 at 33.3 deg C. Victoria has already set a record for this date at 31.6 deg C, beating it's old record of 29.4 deg C set back in 1958.

Footnote added July 31st: Since originally answering this question, we have had two unprecedented days of heat: on July 29th we (YVR) broke our all time temperature record when we hit 34.0 deg C, then on the 31st to my surprise we beat THAT all time record, when we hit 34.4 deg C! I am sometimes humbled by what Mother Nature can throw at us.

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How is humidex calculated?

Tuesday, July 28, 2009 | 01:33 PM PT

Question submitted by Bonnie Almso
(Vancouver, BC)

The Humidex formula is based on the work of J.M. Masterton and F.A. Richardson at the Atmospheric Environment Service (now MSC) of Environment Canada in 1979. It is a standard for Canada, but variations are used around the world. The dew point temperature should be given in kelvins (temperature in K = temperature in °C + 273.1) for the formula to work. The magic number 5417.7530 is a rounded constant; it's based on the molecular weight of water, latent heat of evaporation, and the universal gas constant.

e = vapour pressure in hPa (mbar), given by:
e = 6.11 * exp [5417.7530 * ( (1/273.16) - (1/dewpoint) ) ]

h = (0.5555)*(e - 10.0);
humidex = (air temperature) + h

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I noticed yesterday driving home from work that the sun had an odd orange colour to it. Is this due to an increased particulate matter from the Tyaughton fire?

Tuesday, June 9, 2009 | 03:43 PM PT

Question submitted by Chris St. Louis
(Vancouver, BC)

Here's the background to the effect:
­When the sun is high in the sky, its light travels a relatively short path through the atmosphere to reach your eye, the viewing point of the light. In that sunlight are all of the wavelengths of visible light, and each wavelength is viewed as a different color. The molecules in Earth's atmosphere, mostly nitrogen and oxygen molecules, scatter some of those wavelengths, but not others. Because those molecules are small compared with the wavelengths of visible light, they only end up scattering the shorter wavelengths, sending­ those light beams in all directions, out of the direct path of the light on its way to your eye. This selective scattering of wavelengths, or colors, is called Rayleigh scattering. The sky is blue during the daytime because the wavelengths for violet and blue are the shortest in the spectrum. They are scattered more than any other colors in the light, and as these wavelengths scatter across the sky, that sky turns blue.

As light travels through the atmosphere, hitting those molecules along the way, more and more of the shorter wavelengths are scattered. By the time the light reaches your eye, all the blue and violet has been scattered out, leaving only the longer wavelengths in the sky for you to see. That's why a setting sun turns the sky red, orange, yellow and all shades in between. All of that scattered blue and violet is busy creating a blue daytime sky somewhere else in a different time zone.

This is all happening in a clear sky, with mostly nitrogen and oxygen doing the scattering. If you add other molecules into the mix -- molecules in smog or fire smoke, for instance -- the picture starts to change.

Smog is simply a combination of the words "smoke" and "fog," and it comes from lots of different sources, some totally natural. It's composed mostly of aerosols, solid or liquid particles suspended in the sky. Volcanic eruptions produce heavy smog when they send tons of volcanic ash into the sky. Forest fires do the same when all of that burning matter billows upward, turning the sky nearly opaque.

Here's where it gets a little complicated. Whereas volcanic smog and forest-fire smog are composed of fairly uniform aerosols, man-made smog is composed of countless different molecules and different types of matter, and all of these aerosol particles vary in size. Size is the deciding factor in whether aerosols enhance a sunset's colors or hinder them.

When something like a volcanic eruption or a large forest fire sends particles into the air, it produces smog that blocks only certain wavelength of light. As sunlight moves through this atmosphere, it encounters nitrogen and oxygen, which scatter the blue end of the spectrum, and volcanic or fire ash, which is larger and scatters a good amount of the longer yellow wavelengths, too. What results is an incredibly red sunset until the ash clears.

Even the late afternoon ambient light will appear "redder" than normal. Photographers love this light.. it's considered "soft".

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I have noticed that some jet condensation trails persist longer than others. What are the different atmospheric conditions that contribute to this?

Friday, May 29, 2009 | 11:02 AM PT

Question submitted by Matt Clarke
(Vancouver, BC)

Hi there Matt,
Obviously you spend a bit of time watching the sky! Glad to hear it!

Contrails (short for "condensation trails") or vapour trails are visible trails of condensed water vapour made by the exhaust of aircraft engines. As the hot exhaust gases cool in the surrounding air they may precipitate a cloud of microscopic water droplets. If the air is cold enough, this trail will comprise tiny ice crystals.

Depending on atmospheric conditions, contrails may be visible for only a few seconds or minutes, or may persist for many hours. For the contrail to last a significant amount of time, the airmass at 35-40,000 feet must be very stable. This usually occurs when the upper atmosphere is significantly ridging.

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What are the weather predictions for summer 2009?

Thursday, April 23, 2009 | 03:32 PM PT

Question submitted by Lilly kaetler
(Abbotsford, BC)

Lilly, I get this question so often! Basically long range or "seasonal" forecasting is still a bit of a broad brush type forecast. You won't be able to make day to day decisions with it. So with that being said, the current seasonal forecast, don't hold your breath, for much of Canada is "near normal"!

Check out Environment Canada's forecast at http://www.weatheroffice.gc.ca/saisons/index_e.html.

There are some signs in the Equatorial Pacific Ocean of a slight El Nino developing - which would usually mean a slightly warmer and drier summer pattern for much of Canada. But again, at the moment, this is a very weak El Nino signal and may not materialise.

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What is the key difference and definition between a wind gust and a squall?

Friday, April 3, 2009 | 10:01 AM PT

Question submitted by Parris

Meteorologically speaking a wind gust is defined as the maximum 3-second wind speed that occurs (or is forecast to occur) within a 2-minute interval at a height of 10 meters above ground.

A squall however is a non-frontal line or belt of violent convective activity, sometimes seen with vigorous thunderstorms. Forecasters use the term "squall line" to describe a sudden wind-speed increase of 8 metres per second (29 km/hr) or more, for one minute or longer. It includes several briefer wind-speed changes, or gusts.

A squall however, is often named for the weather phenomenon that accompanies it, such as rain, hail, or thunder; a line squall is one associated with a squall line of thunderstorms that is often hundreds of kilometres long.

In Ontario for example, lake effect snow squalls are common features seen downwind of open and relatively mild water, in a cold windy winter airmass. They are intense, but of limited spatial extent and duration, periods of moderate to heavy snowfall, accompanied by strong, gusty surface winds and possibly lightning. Snow accumulation may be significant in the squall.

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Friday, March 20th, we had our first thunderstorm of the year in Grand Forks B.C. (unusual for mid-March, during such relatively cold temperatures). What conditions would have to be present for a thunderstorm to hit the valley in the evening?

Monday, March 23, 2009 | 11:28 AM PT

Question submitted by Jay
(Grand Forks, BC)

Ok, Jay, first let's denounce the misconception that thunderstorms only occur when it's "warm". As Einstein would say "it's all relative!" Thunderstorms can occur whenever a pocket of RELATIVELY cooler air is introduced to an airmass - at a RELATIVELY warmer temperature - and "lift" or a upward forcing trigger is applied to that airmass. On the date in question, a nasty squally cold front swept through the region.. introducing an area of cooler temperatures aloft to an area that was relatively cool, but much wamer than the air moving into the region. That together with the lift provided by the cold front, set the thunderstorms off.

Also Grand Forks - topographically speaking - is in a bit of a low land. The mountains surrounding the area often provide lift to incoming weather systems.. thereby generating their own thunderstorms (in situ so to speak) relatively easily.

Hope this answers your great question.

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I am not clear on "high pressure" and "low pressure" and their consequenses. Please explain.

Monday, March 16, 2009 | 11:56 AM PT

Question submitted by Tim Hoang
(Surrey, BC)

Wow, Tim, this is a huge question!

Basically the atmosphere can be thought of as a fluid. As this fluid ebbs and flows around the world, we get swells and troughs forming, and these swells and troughs bring certain types of weather regimes with them. That's the "Coles Notes" version, here's the science:

A low pressure area, or "low", is a region where the atmospheric pressure is lower in relation to the surrounding area. Low pressure systems form under areas of upper level divergence on the east side of upper troughs, or due to localized heating caused by greater insolation or active thunderstorm activity. Those that form due to organized thunderstorm activity over the water which acquire a well-defined circulation are called tropical cyclones.

Lows are frequently associated with atmospheric lift. This lift will generally produce cloud cover through adiabatic cooling, once the air becomes saturated as it rises. Thus, low pressure typically brings cloudy or overcast skies, which may minimize diurnal temperature extremes in both summer and winter. Since the clouds reflect sunlight, incoming shortwave solar radiation is less which causes lower temperatures during the day. At night, the absorptive effect of clouds on outgoing longwave radiation, such as heat energy from the surface, allows for warmer diurnal low temperatures in all seasons. The stronger the area of low pressure, the stronger the winds that are experienced in its vicinity.

A red letter "L" is used to denote an area of low pressure on a weather map.

Conversely, a high-pressure area (also called a "high" and denoted with a blue "H" on weather maps) is a region where the atmospheric pressure at the surface of the planet is greater than its surrounding environment. Winds within high-pressure areas flow outward due to the higher density air near their center and friction with land. Due to the coriolis force, winds flow clockwise around high-pressure systems in the northern hemisphere and counter-clockwise in the southern hemisphere. Regions of high-pressure are alternatively referred to as anticyclones. High-pressure areas are generally associated with cooler, drier air as well as clearing skies due to their formation within areas of atmospheric subsidence, or areas of large scale air descent. The strongest high-pressure areas are associated with arctic air masses during the winter, which modify and weaken once they move over relatively warmer water bodies. The area of high pressure associated with the descending branch of the Hadley cell, known as the subtropical ridge, steer tropical waves and tropical cyclones across the ocean and is strongest during the summer. The subtropical ridge also helps form most the world's deserts. Arctic high-pressure systems weaken with height, while subtropical ridges strengthen with height.

Hope this gives you an idea of why we track these areas on weather maps.

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I have noticed over time that there is often increased weather activity after a full moon. Given the moons effect on tide levels there must be at least a small effect. What is the link between the moon and weather?

Friday, March 6, 2009 | 12:35 PM PT

Question submitted by Mark Jennings
(Castlegar BC)

What you may have noticed was nothing more than a coincidence. There is virtually no effect on the weather from the moon.

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I'm learning about clouds in school. Can you tell me what nimbus, cirrus, cumulus and stratus clouds look like and how high they are in the sky? Thanks!

Friday, February 6, 2009 | 10:30 AM PT

Question submitted by Connor Hayden
(Vancouver, BC)

Great question Connor!

Cloud types are widely varied, but in general the layers are split into three - low, middle and high. Low clouds are those found at 0-10000 feet, middle clouds are found from 10000-23000 feet and high clouds are above 23000 feet. Within each layer however there are many variations. There is a great web site that has pictures to show the typical cloud type at each layer: It's called "The Weather Doctor"

Within each layer there are 4 main types of clouds: Cirro form (high and wispy), Nimbo form (dark and stormy with the ability to have the cloud base lower to the surface during precipitation), Cumulo form (heaped, fluffy looking clouds) and Strato form (which are layered clouds). The National Weather Service has a great web site showing the different types of clouds and how they form.

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I am very curious how you go about reaching your predictions. Could you share that info bit by bit with your viewers? I suspect many would be interested in understanding this a little more.

Friday, February 6, 2009 | 10:18 AM PT

Question submitted by John Boer
(Vancouver, BC)

John, I wish it was a simple process, but it's not!

Basically weather forecasting still boils down to pouring over numerical guidance charts, analysing current weather observations and understanding how the atmosphere will change with time under certain circumstances. Environment Canada does actually put some of their operational guidance charts on line - if you want to check them out, they can be found on the Environment Canada web site. There is even a small write up as to how the charts can be used.

I also use model output from other countries when it comes to looking at the longer term forecasts.

It takes me about 4 hours to do all the forecasting for the 18 cities that you see on the weather segment during The National. It takes me another 3-4 hours to forecast for BC and then make all the graphics that are required for the local show.

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Claire, we are considering retiring to Vancouver Island. I know there are varied weather patterns on the Island but can't find a good source for average rainfall. hours of sunshine etc for the major cities / areas. Is there a source you can recommend?

Friday, February 6, 2009 | 10:08 AM PT

Question submitted by Don Lyster
(Calgary, Alberta)

First off Don, welcome to BC! You will love living here.

I get so many enquiries about historical weather records. So here's the answer, for everyone not just those sourcing out potential retirment locations (!). Environment Canada maintains a climate or historical weather on line site at: http://www.weatheroffice.gc.ca/canada_e.html

On the right hand side is a list of further links, click on the "Historical Weather" link and then when you are redirected - click on the "Climate Data Online" link.

I hope this helps.

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What does a "30% chance of rain this morning" mean? Thirty percent of what?!

Friday, January 30, 2009 | 10:02 AM PT

Question submitted by Frank Cosco
(Vancouver, BC)

Oh, this is such a common question. I've taken my answer straight from the Enviroment Canada web site:
The probability of precipitation (POP) is the chance that measurable precipitation (0.2 mm of rain or 0.2 cm of snow) will fall on any point of the forecast region during the forecast period. For example, a 30% probability of precipitation means that the chance of you getting rained over (or snowed over in winter) is 3 in 10. In other words, there is a 30% chance that rain or snow will fall on you, and, therefore, a 70% chance that it won't. It must also be noted that a low POP does not mean a sunny day: it only means a day where the chance of rain or snow is low.

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What is the difference between wind speed & gusts, and how you meausure the gusts of the wind?

Tuesday, January 27, 2009 | 10:23 AM PT

Question submitted by Cody Simmons
(Fruitvale, BC)

Cody, wind measurements are taken with anemometers located 10 meters above ground level (about 33 feet), at official Environment Canada weather observing sites. The latest anemometers are changing from a rotating cup variety of the past, to a new sonic version, with no moving parts, in a replacement program that began about a year and a half ago.

The "wind speed" reported in each observation is an average speed for the most recent two-minute period prior to the observation time. This is also considered the "sustained wind" for routine surface observations (just to confuse matters a bit, in hurricane forecasts, the sustained wind is a one-minute average). This two minute average is calculated from a series of 24 five-second average values.

A wind "gust" is also reported when the peak "instantaneous" wind during the most recent ten-minutes prior to the observation is more than 10 knots greater than the lowest "lull" in the wind during that time. If that is the case, the highest instantaneous wind during that ten minute window is reported as the gust value. The wind speed is recorded by a pen mark on piece of paper held on a rotating drum, attached to the anemometer output. Hence the gusts is the spike in the chart that rolls out with tme.

A squall is a sudden increase in wind speed which is typically associated with active weather, such as rain showers, thunderstorms, or heavy snow, but which lasts much longer than a gust. Squalls refer to an increase in the non-sustained winds over an extended time interval, as there may be lower gusts during a squall event.

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How is "dew point" determined, and why does it matter?

Tuesday, January 20, 2009 | 01:54 PM PT

Question submitted by John Birk
(Kamloops, BC)

John, sometimes the seemingly simplest of questions are the best!

The dew point is the temperature at which the air would become saturated if it were cooled sufficiently. If the air is cooled below this point, spontaneous condensaton of the water vapour in the air will occur. The dew point is actually calculated from two readings on two different thermometers - a dry bulb and a wet bulb thermometer.

The temperature/dew point spread measures the same thing as relative humidity,
but relative humidity is given as a percent. As the relative humidity goes up, the temperature/dew point spread decreases.

So, answering the second part of your question first (!), the measurement of the dew point of the air, essentially gives us the relative humidity of the air.Dew Point values provide useful insights into the characteristics of an air mass at the surface. Generally, higher Dew-Point Temperatures during periods of warm or hot weather will indicate a greater likelihood of discomfort because the air is nearer saturation and therefore less capable of absorbing moisture from the surface of one’s skin. Likewise, low Dew-Point Temperatures will indicate greater comfort during warm weather because moisture on exposed skin evaporates more rapidly, therefore increasing heat loss from the body, making us feel cooler.

Dew Point values can also give insights into the amount of energy available at the surface for the development of thunderstorms. Higher Dew-Point values can indicate a greater supply of heat and moisture at the surface. Greater potential energy in the form of heat and moisture provides better "fuel" for the growth of thunderstorm updrafts.

So the dew point is a crucial piece of the puzzle when creating a forecast.

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Can you tell me why at winter solstice the sunrise actually gets later after Dec 21 and then stays at this same time until the middle of Jan?

Tuesday, January 13, 2009 | 10:22 AM PT

Question submitted by Janice Rosang
(Abbotsford, BC)

Actually it doesn't! What you're probably noticing is a "rounding" error in the publication of the sunrise time. However the sunrise time does remain virtually unchanged for a matter of about a week or so.
And to explain what is going on I'm going to include a discussion about equinoxes as well - simply because you are the second person to ask this type of question. Basically astronomical equinoxes and solstices' are hard and fast explicit moments in time, but they do not mark exact lengths of days etc at our latitude. Here's why:

The seasonal significance of the winter solstice is in the reversal of the gradually lengthening nights and shortening days. How cultures define this is varied, since it is sometimes said to astronomically mark either the beginning or middle of a hemisphere's winter. "Winter" itself is a subjective term, so there is no scientifically established beginning or middle of winter but the winter solstice itself is clearly calculated to within a second. Though the winter solstice lasts an instant, the term is also colloquially - however quite inaccurately - used to refer to the full 24-hour period.

As humans we generally measure the "day" as the time between sunrise and sunset. Sunrise is defined as when the TOP EDGE of the sun breaks the horizon and sunset is defined as when the TOP EDGE disappears below the horizon. Equinox is measured based on the CENTER of the sun's disk, not at the edge. This difference means that at the equinox moment, the day is actually slightly LONGER than 12 hours.

Not only that, but the earth's atmosphere refracts (bends) sunlight coming over the horizon so that the sun appears to have risen even before it really has. This adds 7-8 more minutes to the length of the day at the equinoxes.

Both of these effects combine so that the true 12-hour day for high northern latitudes can occur several days before the Vernal Equinox and several days after the Autumnal equinox. The effect is lessened for latitudes closer to the equator. And the opposite holds true for those latitudes in the southern hemisphere.

In addition, since the earth is not rotating at the actual moment of the astronomical equinox (can't rotate if there is no time change) then only certain points on earth even see a sunset or sunrise at the ACTUAL moment of the equinox. And then the other end of the day for those locations would be before or after the equinox anyway. So no one location on earth can possibly see a sunrise and sunset at the equinox moment.

Still, this third "effect" does not contribute to the lengthening the day as much as the other two.

Hope this answers it!

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How do you calculate the wind chill factor?

Thursday, January 8, 2009 | 09:48 AM PT

Question submitted by Jackie Ward
(Surrey, BC)

Environment Canada has a web site dedicated to the subject of wind chill:

But basically the calculation is as follows:
Tair = air temperature, V = wind (km/h):
WC = 13.12 + 0.6215 × Tair - 11.37 × V (exp 0.16) + 0.3965 × Tair × V ( exp 0.16)

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In response to the flood of questions I've had in regards to the on going threat of the Mtn Pine Beetle to our forests..

Thursday, December 18, 2008 | 04:56 PM PT

Vivian Thomas of BC Forest Services in Victoria (250-387-5728) says "the current cold weather that we are having in the interior is not cold enough to have an impact on Mtn Pine Beetle populations. For this time of year it must be -35 to -40 deg C for several straight days to kill off the pine beetle. The beetles develop a natural anti-freeze that protects them from cold weather. If the cold snap had come earlier in the fall and been -25 deg C for several straight days, then it could have killed off populations when the beetle was more vulnerable."

This from the Canadian Forest Service's website:

"The outbreak is likely to continue until an early cold winter kills overwintering larvae. In fact, it was two back-to-back unseasonably cold fall periods in 1984 and 1985 that caused the collapse of the Cariboo-Chilcotin outbreak. In both of those years, early sustained temperatures in the -30 to -40 deg C range were experienced."

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From my 8 year old daughter Ella; We know that hot air goes up (the top bunk is always hotter than the bottom bunk) but why when we go up the mountain my mum says to dress warm as it is colder the higher you go?

Wednesday, December 17, 2008 | 07:12 PM PT

Question submitted by Sarah Renzoni
(West Vancouver, BC)

In the wonderful words of Einstein "it's all relative"!

You see on a small scale, relative ambient air temperatures are the driving force of air circulation. As your mother notes, Ella, warm air rises and cold air sinks. However on a much much larger scale, (weather systems and atmospheric layering scale) the air thins with height. Less air means less trapped warmth. So the higher you go, say up a mountain, generally the cooler the air. However this is not always the case.. sometimes a layer of warm air can be found on top of a mountain - what is meteorologically known as an "inversion". This occurs where cold arctic has sunk and travelled into a valley floor.. forcing warm air to rise above it.. much like as Mum notes, happens with your bunk beds!

Hope this answers your question!

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Could you explain the difference between "rain" and "showers", both in how these terms are used for the layperson, and what they mean to meteorologists?

Tuesday, December 16, 2008 | 07:13 PM PT

Question submitted by Vinit
(Vancouver, BC)

Vinit, this is one of those great questions, that on the surface, sounds ridiculously simple to answer! But it isn't! Here's the "simple" answer!

A rain shower is a brief intermittent period of rain. Environment Canada considers showers to last longer than 15 minutes but not as long as an hour, and may have a change in precipitation intensity. It's actually quite complicated for the weather observer out there to decide when the showers have ended and the steady rain has begun!

Needless to say, for the layperson, when forecasters call for showers, they expect to see breaks in the precipitation.

Confused?! I hope not!!

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Given the mix of latitude, frontal systems, water and mountains, and a shifting winter freezing level, I would guess Vancouver and region is about the hardest place I know to predict the weather reliably.

Friday, December 12, 2008 | 11:05 PM PT

Question submitted by Peter
(Vancouver, BC)

Question: Given the mix of latitude, frontal systems, water and mountains, and a shifting winter freezing level, I would guess Vancouver and region is about the hardest place I know to predict the weather reliably.
Is this true, and are there any other populated areas of Canada that are as hard or harder to forecast?

Peter, oh how I wish that were true! Actually nearly every city in Canada has its own set of forecasting difficulties! I would have to be honest and say that Calgary, AB is possibly the most frustrating place to forecast for. Knowing that a strong Chinook wind can raise temperatures suddenly and dramatically is not enough, a forecaster has to determine if and when and to what degree the Chinook will blow, or watch the forecast high be missed by 10-15 degrees! Whitehorse is another nightmarishly hard place to get right, especially in the Spring & Fall when arctic air can settle down the valley and create widespread fog. Oh and Ottawa, being also in a valley, can see its forecast high missed by 10 degrees if the wind isn't strong enough to scour the cold air out the valley.

Now forecasting for Vancouver does have its challenges too! We live so close to the ocean that the influence of that body of water is almost as big as the incoming weather systems!!

Let's say this job keep me on my toes and has taught me humility!

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Tell me about the eastern Pacific ridge and the lack of snow in the coastal mountains.

Friday, December 12, 2008 | 07:21 PM PT

Question submitted by Chris Galati
(New York, NY)

Question:I've read that an "eastern Pacific ridge" is preventing winter storms from hitting the Vancouver - Whistler area. Often this ridge breaks up around mid to late December, though. Can you elaborate on this ridge and also share your thoughts on the lack of snow in the coastal mountains? We're heading to Whistler in a few weeks and are hoping for snow! Thank you.

First off Chris - welcome to Vancouver!

Next the question. During La Nina winters we often see a high pressure ridge set up in the East Pacific with dryer than normal conditions in Southern California and wetter than normal conditions in the Pacific Northwest. Most of the storms that develop ride up and over said ridge and into Southern BCWashington/Oregon bring more precipitation to these areas. For the past three months however, the Equatorial waters that drive these events have been "ENSO neutral", meaning that we are in neither an El Nino set up, nor a La Nina set up, and as a result we really haven't seen a predominant eastern Pacific ridge set up either.

What we have been is lucky (or unlucky if you're a skier).. it has been a very dry Fall, and the local area ski hills have struggled to maintain a lower elevation base. That being said, it looks like our weather is finally changing, and good Arctic push is setting up. All the local ski hills - and more importantly Whistler (which opened it's record breaking Peak to Peak gondola today look set to get a good dump of snow over the next 24 hours.

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I am wondering how much snow has to be in the forecast to generate a snowfall warning. And while we are at it, how about for a rainfall warning?

Tuesday, December 9, 2008 | 11:48 PM PT

Question submitted by James
(Vancouver, B.C.)

Wow this sounds like such an easy question!

Basically Environment Canada issues a snowfall warning when a "regionally specific" snowfall amount is expected within a 24 hour period. The term "regionally specific" is crucial here. For example: for The North Coast - Inland Sections, the amount is 25 cm or greater, for the Coastal Sections - it is 10 cm or greater, and yet for the Greater Vancouver or Greater Victoria regions, the required snowfall is only 5 cm or greater. Rainfall warnings are similarly spatially specific - most coastal regions will get a rainfall warning when 50 mm or greater are expected to fall within 24 hours or less. For the interior of BC, the amounts are tapered down to 25 mm or less.

Now that being said, interior regions are broken down even further for snowfall amounts.

For a full description of all warning criteria breakdowns I would suggest you drop Environment Canada a note.

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I'm researching summer weather patterns in preparation for a cruise around Vancouver Island in 2009. Can you explain "summer advection fog"?

Tuesday, November 25, 2008 | 07:20 PM PT

Question submitted by Wayne Saewyc
(Richmond, B.C.)

Advection fog is formed by the slow passage of relatively warm, moist, stable air over a colder wet surface. It is common at sea whenever cold and warm ocean currents are in close proximity and may affect adjacent coasts. A good example is provided by the frequent dense fogs formed off the Grand Banks of Newfoundland in summer, when winds from the warm Gulf Stream blow over the cold Labrador. Equally this phenomena is common during the summer months around Vancouver Island.
Don't be too put off Wayne, from taking a criuse next summer, the presence of this fog can often make for spectacular photos!
Have a great cruise.

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When I look through the Environment Canada database, for most weather stations I find, very often, that on any given day the record low and record high are one year apart. Is there anything about weather patterns, that you know, that could explain this??

Monday, October 27, 2008 | 05:26 PM PT

Question submitted by Mike


I get a lot of these type of questions. As you noted for example, on October 25th Hamilton, Ontario's record low was -2.8 degrees C set in 1962 and it's record high was 25.0 degrees C set just one year later in 1963. Unfortunately there is no tie between these kind of record events. I wish there was! It's purely part of the nature of a chaotic fluid (i.e. the atmosphere) moving through the course of space and time.

After thought: I just have to add an extra note here, because today Claresholm, AB saw something even more unusual than records set merely one year apart.. a record low and high temperature set all in one day! Yes, they started this morning at -10.1 deg C, which tied a record low set in 2004, meanwhile warm winds helped crank the temperature in the afternoon to a very pleasant 23.1 deg C breaking their old previous record of 22.2 deg C set back in 1953!

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My husband and I 'feel' it will be a cold/snowy winter here on the Island. We've even cut/stacked 6 truckloads of firewood just in case. What's the forecast for 2008/09 winter season, Claire?

Monday, September 22, 2008 | 05:48 PM PT

Question submitted by Carol Elder
(Nanaimo, B.C.)

Funny how the change of season gets people thinking ahead!

I am very nervous about giving out seasonal forecasts - mainly because day to day weather variances often bear little resemblance to the seasonal forecast. On a very general level, the relative warmth of the Pacific ocean around the equator, often gives us an idea as to whether or not the upcoming season will be warmer or cooler than average.

Every two to seven years off the western coast of South America, ocean currents and winds shift, bringing warm water westward, displacing the nutrient-rich cold water that normally wells up from deep in the ocean. The invasion of warm water disrupts both the marine food chain and the economies of coastal communities that are based on fishing and related industries. Because the phenomenon peaks around the Christmas season, the fishermen who first observed it named it El Niño (“the Christ Child”). In recent decades, scientists have recognized that El Niño is linked with other shifts in global weather patterns.

The equatorial Pacific is presently considered to be "ENSO-neutral" - meaning conditions are neither warm nor cold. Very weak below-average sea surface temperatures (SSTs) still exist near the dateline, and weak above-average SSTs are present in the eastern equatorial Pacific. There is a 90 percent probability of ENSO-neutral conditions persisting over the coming season.

So basically - we're looking at a "normal" lead into winter!

Environment Canada also issues seasonal forecasts: check out

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Does the Chilcotin have the highest average daily swings in temperature in Canada? If not, in which communities would it be higher?

Tuesday, September 9, 2008 | 12:50 AM PT

Question submitted by Junah
(Lumby, B.C.)

Wow, that's a fantastic question! And you're thinking in the right direction! Basically anyone living in a "continental" region in this country, that is away from a large body of water, will see more extreme daily temperature ranges or swings than someone living by the moderating influence of water.

I do believe however that Southern Alberta - namely around Pincher Creek - see's even greater swings than the Chilcotin region of BC because of the occasional warm Chinook Winds that blow through that particular area. This "exagerates" the potential for an already wildly swinging temperature regime. For example in Pincher Creek, the temperature rose by 41°C (from -19°C to 22°C) in one hour in 1962 when a particularly strong Chinook blew through.

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I am thinking about a move to Vancouver Island in the new year. Can You tell me what area has the least rain and gets the most sun?! I dread the rain, but I know it's more than the Okanagan gets anywhere!

Tuesday, September 2, 2008 | 05:37 PM PT

Question submitted by Angie
(Kelowna, B.C.)

Oh Dear Angie!! Be warned - the Island is much wetter than your current residence! Now that being said Victoria is historically much less wet than say Tofino. The "best" locations for dryness on the Island are those areas that fall in the rain shadow of the central highlands along the spine if the Island. Very broadly speaking areas on the east side of the island will be drier than areas on the west. I would however go check out the historical weather information published by Environment Canada.. the data that you are particularly interested in is the climatological rainfall amounts for each month for the various sites. Go to:

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Can you explain why as one travels east over the BC mountain ranges the climate gets progressively drier, but travelling from Vernon over the Monashee Mountains, you don't see the same effect?

Thursday, August 21, 2008 | 10:49 PM PT

Question submitted by John Campbell
(Vernon, B.C.)

Here's the full question:
"I am a bit confused about one thing. As you travel Eastward over BC mountain ranges the climate gets progressively drier on the Eastern side of the mountains. For example, Golden is much drier than Revelstoke, Princeton much drier than Hope. BUT, we you travel from here (in Vernon) over the Monashee Mountains over to Nakusp and Revelstoke, it gets much much wetter."

John, great question but you are essentially mixing up two local weather effects here.. the "rain catchment" effect and the "rain shadow" effect. Basically airmasses crossing over higher terrain are usually rained out on the windward side of the mountains and end up much drier on the leeward side of the mountains. But this is not always the case.. sometimes local weather effects override the climatological effect of the "larger scale topography".. and I believe that's what you're seeing here.

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I was in California coast and was thinking about our west coast. Obviously because we are north we are much cooler but what makes California have so much sunshine year round, and BC coast have ALOT more cloud and rain.

Friday, August 8, 2008 | 06:00 PM PT

Question submitted by Dave Seminchuk
(Burnaby, B.C.)

Hi there Dave,

Welcome back to "cloudy ol' BC"!! Good question. Now part of the answer purely is perception. San Francisco is actually a rather foggy/cloudy city, thanks to the warm air from inland (where it gets quite hot in the summer) clashing with the cold air coming across from the surrounding Pacific Ocean and the SF Bay. When that happens, fog forms. But that's a rather local effect.

But in a more general context, BC's coastline is cloudier due in part, to the path of the jet stream. This ribbon of fast moving air aloft, carries with it weather systems (more specifically cloud bearing weather systems). Due to the latitude of Canada and the tilt of the Earth, we lie in a more temperate zone.. and the jet stream tends to feed these systems along our coastline for longer periods of time. Hence, on average, we end up with cloudier conditions for greater periods of time in the year than they do in, say, California.

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Here are two great questions that I got, in regards to Environment Canada's UV Index and secondly in regards to the recording of "hours of sunshine".

Friday, August 1, 2008 | 12:19 AM PT

Question submitted by Jason Williams
(Burnaby, B.C.)

1) How do they forecast the UV index for all the different areas of BC
when there is only 1 or 2 UV monitoring stations for the entire

2) I was looking back through the Environment Canada database and
noticed that there are currently no weather stations in the BC mainland
that record hours of sun. If I look 10 years ago or even 40 years ago
there were 20 to 30 weather stations that measure hours of bright
sunshine in the BC interior. Why is this the case?

For the answer, I went to Environment Canada. Here is their answer:

"UV radiation is very strongly seasonally and latitudinally-dependant.
The day-to-day variation due to the presence and strength of high
pressure systems in the upper atmosphere is important during the summer
but still very small compared to the seasonal and latitudinal influence
and of course whether the sky is cloudy or clear. Consequently the rough
value of the index for any location and time can be predicted far in
advance. Measurements of UV radiation (taken on Saturna Island) are
important for research and monitoring but not so critical to producing
the day-to-day forecast.

Regarding sunshine hours, the weather service is no longer officially
recording hours of sunshine.
There are several reasons but most important is that the instruments
used to record sunshine are outdated and crude. A close second reason is
the fact that NAV Canada has taken over the contracting for weather
observations at the airports where sunshine hours were previously
measured by Environment Canada staff or Contractors. Bright sunshine
hours are understandably of little value to flight operations and hence
Nav Can has not made their measurement a requirement at these airports
since they took over.

More sophisticated measurements of solar radiation are now possible and
we expect these measurements to eventually form the basis for
determining sunshine hours. There are apparently very strong
correlations between certain wavelengths of solar radiation and the
previously measured bright sunshine hours. This has implications for
calibrating the past bright sunshine hours to newly measured solar

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It has been recently stated that BC was undergoing a heat wave. However, it doesn't appear to be happening here. Apparently, the average temperature in Northern BC is below average?!

Tuesday, July 29, 2008 | 05:54 PM PT

Question submitted by Jake Van der Meer
(Prince Rupert)

Jake.. first off remember that "heat waves" are defined as merely 3 or more days with temperatures coming in 7-10 deg C above seasonal. Furthermore, the heat wave to which you are referring may not have been written explicitly in reference to Prince Rupert. I have done some quick checking and it turns out that May was indeed a slightly warmer than seasonal month for you with an average high temperature coming in at 12.7 deg C versus 12.3 deg C as a normal. However both June and July have come in below seasonal.

To check up on your own local climate conditions, go to the following web site.

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Is it at all conceivable that we can somehow extract some of the extremely cold temperatures from our upper atmosphere to re-cool our Polar Regions?

Tuesday, July 29, 2008 | 05:28 PM PT

Question submitted by Gary

Gary.. first off I'm adding the rest of your question here:
"I understand that the city of Toronto is running water pipes deep into the Great Lakes to serve as Air Conditioning for Business Towers...this is probably far fetched, but in the future could we not envisage super light carbon conduit materials that can be held aloft by a series of (solar powered) satellite space anchors that draw surface air into a super-chilled atmosphere and return the cold air back to the polar caps....sci-fi (for sure)?!"

This is such a great question.. but yes a little far fetched. The biggest issue with all this is in regards to the inability to transfer fluids/gasses/energy through very different layers of the atmosphere without losing much of the attributes of the actual fluid/gas/energy (simply put) to friction.

If we could get around this "loss through dispersal" effect, then I think something like ground level ozone (a real problem for us) would be the first gas we would need to "move". We could simply extract it and pump it back into those regions in the atmosphere undergoing ozone depletion!!

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What factor would keep Hurricane Bertha anchored for three days in the same position and, pushing to the north all eastbound weather?

Tuesday, July 15, 2008 | 05:23 PM PT

Question submitted by Andrew Goudey

Andrew, Bertha is encountering an area of rather weak steering winds at high altitudes and a surface area of high pressure to the north, meaning that the forward motion of the storm is severely limited.
For really great discussions on Atlantic Hurricanes, their forecasts and potential tracks, you should check out the following:
and read the "forecast discussion" from that link.. it'll give you great insight as to where the forecasters think the storms are going.

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I'm aware the Coriolis Effect drives low pressure systems counter clockwise in the Northern Hemisphere and clockwise in the Southern Hemisphere. So, is this why drains tend to drain counter clockwise in the Northern Hemisphere and clockwise in the South?

Monday, July 7, 2008 | 05:22 PM PT

Question submitted by Sean (Kamloops)

In physics, the Coriolis effect is an apparent deflection of moving objects when they are viewed from a rotating frame of reference.

In a meteorological frame of reference, as air moves from high to low pressure in the northern hemisphere, it is deflected to the right by the Coriolis force. In the southern hemisphere, air moving from high to low pressure is deflected to the left by the Coriolis force.

The amount of deflection the air makes is directly related to both the speed at which the air is moving and its latitude. Therefore, slowly blowing winds will be deflected only a small amount, while stronger winds will be deflected more. Likewise, winds blowing closer to the poles will be deflected more than winds at the same speed closer to the equator. The Coriolis force is zero right at the equator.

When talking about a fluid in a toilet bowl however, the Coriolis force is completely overcome by the local mechanisms that start the water swirling in the bowl. It is a common misconception that water will flow down a drain or a toilet in a direction depending purely on the Coriolis force.

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I thought temperature drops as you travel North, so why is Fairbanks Alaska sometimes warmer during June and July nights than many places in BC?

Tuesday, July 1, 2008 | 05:26 PM PT

Question submitted by Justin Price (Vernon)

Essentially, Justin, if we didn't have an atmosphere and the earth simply spun around the sun as it does right now, then the poles would be very cold and the equtorial regions hot and the temperature would linearly fall off as you moved from the equator to the poles. However, thank heavens (!), we have an atmosphere and that atmospheric fluid allows for eddies and bubbles of heat to travel much farther poleward than you would expect. When the weather in the north (Alaska, Yukon for example) is much warmer than the south (interior of BC even) it is simply because the motion of the atmospheric fluid is carrying waves of warm atmosphere to these regions. As a forecaster, this is one of those times where the jet stream is a big player. That thin (see below) ribbon of very fast moving air at high altitudes will have migrated north, allowing those bubbles or pools of warm air to travel north. The warm air will linger in those northern regions until the jet stream falls south again.

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It is said that the Jet is at approx 30,000 ft. However, I have never heard how "thick" or how "wide" the jet stream can be??

Monday, June 23, 2008 | 07:17 PM PT

Question submitted by Terry Bolton (Salt Spring Island)

Terry, you will notice that I do not use the jet stream very much on my weather presentations! I strongly believe that it is a term that is often over-used and also frequently used misleadingly. It is basically a 'ribbon' thin layer of very fast moving air aloft. However to refer to the jet stream singularly is incorrect. Basically there are many ribbons of fast moving air above the earth. Some of these ribbons become more pronounced and can force very large weather systems (that extend deep into the atmosphere) to move around.

The NOVA online web site has a great discussion on the existance of jet streams:

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This spring has been really cold... why is that? Will next year be warmer, or is this a new trend?

Sunday, June 22, 2008 | 08:53 PM PT

Question submitted by Meg (New Westminster)

I get so many questions about the "state of our weather" and whether or not we can expect a "warmer or sunnier" summer. Unfortunately these questions are far more difficult to answer than they seem.

There's an old saying in the "weather industry" that states the following.. "weather is what you get, climate is what you want". Generally most of us would like see seasonal average temperatures and weather during any time of the year, but that simply isn't likely. The atmosphere is a fluid and carries too many variations within it for us to really hope to get seasonal weather all the time.

As far as forecasting for the seasons goes, well, to be quite honest, we're horrendously bad at it. We barely have a fundamental grasp of all the forcing agents at work on short term weather, so much so that our long range forecasts are often grossly misleading. That being said, Environment Canada does issue 'seasonal outlooks'. You can check them out at the following:


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