CBC British Columbia
Questions for Claire

Archives: December

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."

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!

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!!

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!

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.

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.