How do you explain the cool summer in southern British Columbia?

August 20, 2007 10:43 AM

Can anyone tell me why the North Pacific high is so far south this year?

Every year summer arrives here on the west coast of North America when a high pressure zone builds up off northern California. This ensures a beautiful warm and sunny summer here in southern British Columbia, as low pressure systems are diverted north to the Alaskan panhandle and northern BC.

This year though, the weather has been variable, cool and rainy. The North Pacific high is a lot further south than it normally is. It's due west from Los Angeles at the moment, and funnelling low pressure systems right into us.

Up to date meterological analysis is actually pretty hard to find on the web, hence my question here. What are the theories about why the high has formed like this this year?

(Bonus points if you can point me to good online real time analysis for this region).

posted by salishsea to science & nature (5 comments total)

Here's my guess, global dimming is responsible for decreases in the amount of solar radiation that reaches the Earth. In some locations the reduction in energy is as much as 22%. This reduction in energy is partially caused by fine particle air pollution directly blocking solar energy and partially caused by sulfur dioxide particles forming both more clouds and more reflective clouds. (BBC documentary on this subject.

Seasonal weather shifts are pretty much defined by the changes in the amount of solar energy that reaches the surface of the Earth. When these changes are artificially buffered by pollution some of the changes may fail to occur.

In the documentary linked to above, they suggest that a seasonal change in the weather pattern similar to the one you're observing, one that normally brought rains to sub-Saharan Africa, failed to occur because of pollution and resulted in a massive famine.
posted by 517 at 1:56 PM on August 20, 2007

Don't know about you, but over here, our shitty summer weather has been blamed on La Niña.
posted by Helga-woo at 3:22 PM on August 20, 2007

I was going to say the same thing. Apparently the ENSO has been funky the last few years.
posted by Steven C. Den Beste at 4:59 PM on August 20, 2007

Thanks, 517; now that you've been brave enough to break the ice with your guess, I can muster mine up.

Speaking of ice, I would try to tie it to increased melting of sea ice in the Northern hemisphere.

Ten days ago, or so. sea ice in the arctic had reached the lowest level in recorded history, with ~30 days to go in melting season. Since ice reflects a great deal of sunlight, and open sea absorbs light relatively efficiently, the fact that we have the greatest amount of open sea in the recorded history of the arctic may mean (and I emphasize may) that we have the greatest rate of solar heating in the arctic sea we have ever seen, and consequently a much greater than usual total amount of melt water.

This melt water is much less dense than the ordinary sea water of a similar temperature it encounters as it melts because it lacks the dissolved salt of the ocean water, so instead of sinking it spreads over the surface of the sea, making surface temperature low to the south to a distance which depends on the amount of melt water.

That distance to the south is much greater this year than in previous years because more ice has melted, and that has had the effect of displacing the pattern of weather systems which ordinarily butt up against the cold surface water to the south, including your North Pacific high.

In short, there is a much larger than usual cap of cold surface water surrounding the North Pole than usual this summer (according to this argument; I don't actually know), and that has had the effect of displacing your North Pacific high to the south of its usual positon.
posted by jamjam at 7:52 PM on August 20, 2007

Fantastic answers...it's interesting to know about the various variables at play. Weather is so local here that I can't rely on forecasts for nearby major centres like Vancouver. When I really need to know the weather (if I am heading out on the ocean for example) I put together my own forecasts based on consulting a nuber of variables including the pressure slope, local wind direction, weather maps, forecasts from a variety of weather stations, radar and good old observation and experience. From that I can guess what's going to happen within a decent tolerance, but predicting weather on the BC coast is a mug's game at the best of times.

At any rate, the idea that I can suss the longer term seasonal trends is intriguing. I usually just rely on El Nino and La Nina predictions from which I can predict general seasonal trends. This is useful for ordering firewood for example. Thanks to these answers I have a couple more variables to play with.

Much appreciated!
posted by salishsea at 11:42 PM on August 20, 2007