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Your Questions - British Columbia

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Claire Martin on weather

CBC Meteorologist Claire Martin (CBC)
Are you wondering about the weather, with winter on its way?

This is your chance to ask CBC Senior Meteorologist Claire Martin all your burning (or raining, pouring, sleeting or snowing) questions.

Claire recently moved to Vancouver, and now joins Ian and Gloria with her forecasts on CBC News Vancouver at 6 p.m.

She has twice been chosen as the "Best Weather Presenter in the World" by her peers at the International Weather Festival.

Use the form below to send your question to Claire, and check back for her answers.

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Comments: (21)

Ian Gill (Huntingdon_Qc) wrote:

Miss seeing you regularly on The National. Vancouver's gain is the nations loss.

Posted October 27, 2007 09:46 AM

Jessica Mallory (Williams_Lake) wrote:

Why has the ozone layer depleted faster over the Antartic then in other areas of the world?

Posted October 24, 2007 08:03 PM

Jessica Williams (Williams_Lake_BC) wrote:

Q| I was wondering what it is that makes air currents travel in a constant flow in the same direction. In other words what makes the prevailing westerlies "prevail"?

A| Simply put: the rotation of the earth!

Posted October 24, 2007 10:51 AM

Bradford Temple (Williams_Lake) wrote:

During the last three summers I have been sailing in Comox British Columbia. The summers of 2005 and 2006 were very hot with very little wind but this year much to my pleasure was quite the opposite it was windy and very cold for most of the summer, i was just wondering what may have caused this switch in the temperature and the wind


Posted October 24, 2007 10:00 AM


Q| How much snow on average does Vancouver recieve anually? We in Northern ontario are used to it and have the removal equipment to handle traffic problems.

A| Very roughly speaking Vancouver gets 50 cm of snow annually.

Posted October 24, 2007 07:43 AM

Angela Forseille (Williams_Lake_BC) wrote:

From what I have read the Coriolis effect has a dramatic effect on large-scale oceanic and atmospheric circulation. It also is responsible for the direction of rotation of large cyclones. Does the Coriolis effect affect the direction of large storms or just their direction of rotation? Also how does it influence BC's weather?... Does it control where currents come from?

Posted October 23, 2007 10:23 PM

Lucille Robertson (Niagara_Falls_ON) wrote:

Dear Claire:
I do not have a question. Good to see you again.
I am just very happy to see you predicting any weather pattern... even the rainy forecasts son't seem as bad because you're smiling so much.

I enjoy reading the Q&As; they are educational.

Posted October 23, 2007 01:05 PM

Paul Wiltse (Powell_River) wrote:

Q| When all the weather on the coast seems to come from the west, off the ocean, why is it our bad weather in Powell River seems to come from the south-east, from the lower mainland?

A| Hmmmm.. you have to define "bad" weather.

But if you mean wind and rain, then remember that local topographic and forcing effects generally override prevailing upper level wind affects.

Posted October 22, 2007 11:59 PM

Ian Higgins (Williams_Lake) wrote:

Q| How much of the air pollution in Canada and the United States is due to the prevailing westerlies bringing it in from Asia?

A| Very little hard core science is around in regards to pollution transportation coming across from Asia.

Those measuring atmospheric chemistry over Canada typically have very little information about potential significance of trans-Pacific transport, particularly on short time scales when most measurements are taken.

Some investigation however suggests that Canadian aerosol and chemical data may need to be reconciled with intercontinental transport to explain synoptic-scale variability, particularly for enigmatic high episodes that appear to have no local origin.

Posted October 22, 2007 02:06 PM

Garrett (Williams_Lake) wrote:

Q| How much will melting Arctic ice affect sea levels? Will it be enough to damage coastal towns? Or is it just people jumping to conclusions?

A| Melting glaciers and land-based ice sheets will slowly contribute to rising sea levels, threatening low-lying areas around the globe with beach erosion, coastal flooding, and contamination of freshwater supplies. (Sea level is not affected when floating sea ice melts.)

Unlike much of Canada, at particular risk are island nations like the Maldives; over half of that nation's populated islands lie less than 6 feet above sea level.

Even major cities like Shanghai and Lagos would face similar problems, as they also lie just six feet above present water levels.

That isn't to say that rising sea levels wouldn't severely impact coastal Canada. Canadians will have to rethink city and town infrastructure in those low lying areas most at risk - the rise in the sea level however, is something that will occur over the course of several years, and hence potential property loss can be mitigated by preventative action.

Posted October 22, 2007 02:04 PM

Rohan Keenan (Williams_Lake) wrote:

Q| What happens if acid rain freezes? Does it create a "acid" snow?

A| Hmm...good question...

Acid rain has a different condensation nuclei to "regular" rain, and that would affect the temperature at which the rain drop would freeze.

But - yes - acid rain can freeze - and it would exhibit the same attributes to regular rain if it turned to snow. It would continue to eat away at rocks, causing them to erode and crack.

Moisture in the cracks would then freeze during the winter months, expanding as the water freezes, making the cracks even larger and exposing even more surface area to the acid rain/snow and further erosion.

Posted October 22, 2007 02:00 PM

Bill Lee (Vancouver) wrote:

Q| Will you play some of Bob Fortunes old chalkboard weather 'casts?

A| No chalk boards for me - unless there's a major computer melt down!

Q| And why is the weather always seen top down, and never sideways for the various microclimates up our slopes, and the way the clouds bunch over Vancouver Island, disperse over the Gulf Islands, and then bunch up on the North Shore?

A| I always show weather "top down" as you call it, as that's the view that most people are familiar with.

If we start to show "side" views of an area, we (meteorologists) have found that our viewers become more mesmerized with the actual view of the topography rather than the forecast content of the show.

I would rather be clearly understood - with everyone getting a good solid idea of their own geography - than show a visually confusing side shot.

Posted October 21, 2007 10:52 PM

Elly Steiner (Prince_George) wrote:

Q| When is sunrise and sunset for a given location? In other words, you indicate sunset for Vancouver to be for example: 5:45 pm, but is that when the sun sets along the ocean horizon or at some other point in it's travel. Further, if one lives in a valley surrounded by the mountains, when would sunset occur, when it drops behind a mountain or when the light level reaches a certain intensity that can be measured?

So is the time of sunrise or sunset when the sun disappears behind the horizon at one's location or when a certain intensity of light is ambient? I would think that the latter would be more scientifically accurate and consistent, location to location, but I'd also think that the former is what most people think? The former would be very inaccurate on an ocean horizon vs. a mountainous horizon.

A| Great question.

Essentially for sunrise/set times the earth is considered to be essentially flat and sunrise/set times conventionally refer to the times when the upper edge of the disk of the Sun is on the horizon, considered unobstructed relative to the location of interest.

Atmospheric conditions are assumed to be average, and the location is in a level region on the Earth's surface. However the mountains do make a huge difference.

Here's a great website for this, from the U.S. Naval Observatory.

Posted October 21, 2007 05:52 PM

Jason Williams (Vancouver) wrote:

Q| Someone once told me that in BC the average summer temperature generally decreases as you travel West and North. Kamloops in both West and North of Kelowna and Penticton, yet has hotter summers than these two Okanagan cities. All three cities are close to large lakes and similar elevations, so how can this be?

Thanks, Jason

A| Our "interior" sites have a far stronger "forcing" factor when it comes to average weather conditions- namely the rain shadow affect of the mountains around them.

Furthermore, depending on those sites that have "average" winds working in their favour, they will see minor variations in comparison to other local sites, for daytime high averages.

Unfortunately when we talk about temperatures falling off on average by latitude, we're talking very large distances. For example, Northern B.C. sees the summer temperature averages drop off faster than southern B.C.

Posted October 20, 2007 06:48 PM

James F. (Nelson_BC) wrote:

Q| If, on one particular day, there was a 20% chance of precipitation, and it IS raining, is there an 80% chance of it stopping?

A| No - unfortunately.

When we talk about probability of precipitation - we're talking spatially across any given area there is a (say) 2 out of 10 chance that you will see some rain.

But remember that anything under (and including) a 40% risk means that there is a better chance that will see nothing.

Posted October 20, 2007 10:15 AM

Jay Denomme (MissionBC) wrote:

Q| I'm an avid skier, And was wondering what i should expect this winter for the south coast mountains? I've heard La Nina will be making an apperance. Will this be the case?

A| La Nina at best will cool off the south coast slightly below seasonal temperatures - which means that rain bearing weather systems have a slightly greater chance of bring snow to the hills.

I believe however that after last year, Whistler couldn't possibly get a "better" year!!

Posted October 20, 2007 07:36 AM

Mrs O'Kana (Vancouver_BC) wrote:

Q| For those of us who are carless walkers and cyclists.. what can we expect Global Warming to deliver us this year on the West Coast?

A| Global warming does not occur on a daily basis - it's a trend one will experience over the next decade. Like you, my walks to work recently have been cold and wet and not at all indicative of global warming!

Q| Can you tell us anything about the approaching storm season? Is there any chance we'll experience the miserable and violent storms we saw last year.

A| We always do - it's the beauty of living on the west coast!!

Posted October 19, 2007 03:09 PM

Loyd Csizmadia (Williams_Lake_BC) wrote:

Q| Hi Claire:
As a Geography 12 teacher, I would like to involve my class in this Q & A exchange. We can begin with my question:

Please explain the relationship between the jet stream and the position of frontal weather systems along the west coast of North America.

Loyd Csizmadia

A| The jet stream is a thin ribbon of very fast moving air found in the atmosphere at around 11 kilometers (36,000 ft) above the surface of the Earth.

They form at the boundaries of adjacent air masses with significant differences in temperature, such as of the polar region and the warmer air to the south.

The jet stream is mainly found in the tropopause, at the transition between the troposphere (where temperature decreases with height) and the stratosphere (where temperature increases with height).

The major jet streams are westerly winds (flowing west to east) in both the Northern Hemisphere and the Southern Hemisphere, although in the summer, easterly jets can form in tropical regions.

The path of the jet typically has a meandering shape, and these meanders themselves propagate east, at lower speeds than that of the actual wind within the flow.

Large weather systems that extend high into the atmosphere will find themselves getting steered across the globe by these strong winds. So, on a very broad and general scale...a jet stream can be thought as the steering flow of very large weather systems.

Posted October 19, 2007 07:11 AM

Susan (Whistler_BC) wrote:

Q| I thought I heard you say something on the forecast tonight (Thurs Oct 18th) about why it wasn't as windy as predicted. We tried to windsurf today near Nanaimo and the wind only blew briefly in the morning. The forecasters were really wrong! What did I miss?

A| Cold air tends to sink...so cold core systems tend to drag down stronger winds from higher up in the atmosphere.

Basically the weather system that we saw come in was "ex tropical" so it was essentially warm in the core. As warm air tends not sink, it didn't drag down those strong winds.

The forecast on the winds was essentially a bust as we all thought that although it was a warm cored system it had intensified sufficiently over the ocean to bring across some good winds - but in the end it didn't. Sigh!!

Posted October 18, 2007 07:23 PM

Giorgio Petricca (Red_Deer) wrote:

Q| You do a fabulous job of weather reporting!

Question: I am planning on driving to Vancouver from Red Deer on November 1, 2007....are there any weather warnings and/or snowfall expected en route?

thank you kindly,


A| Hmmm...check the forecast about 48 hours prior!!

Posted October 18, 2007 07:22 PM

Robert D. (Vancouver) wrote:

Q| For many years I have heard meteorologists use the phrase "rain tapering to showers". Now I know what rain is, I know what a taper is, and I know what a shower is, but putting those three words together means nothing to me; it's a noun nouning to a noun. What does it mean?

A| Great point!

Basically for meteorologists "showers" are brief and intermittent periods of rain.

The reasoning in part, for this goes back to the early weather pioneer days when observations were done essentially to help bring aircraft safely to ground.

In order to try to let pilots know that the rain was not "consistent" in nature, forecasters came up with rules about the length of time that the rain fell being crucial as to whether or it was called "showery" or not.

Furthermore, on a forecasting level - the term "showers" indicates a convective atmosphere (which I won't get into) - and that is another crucial element of synoptic understanding for a weather forecaster when he or she is looking at a weather observation.

However on a grammatical level - the term "tapering" is probably being used incorrectly. I was never as good at English as I was at meteorology!!

Posted October 18, 2007 05:11 PM

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