Yeah, I'll admit that when I started writing this piece a few days ago, things were looking much different for Thanksgiving in Southern BC.
Well here we stand, the Lower Mainland is on the brink of the impending rainy season. We well know this, Vancouver.
As we dive into another shoulder season that is autumn, the jet stream will tend to become more zonal, replenishing the snow levels in the British Columbia mountain ranges and eliciting grins out of mountaineers and skiers alike.
Is Vancouver running out of time to experience another taste of 20°C before Spring 2015?
An excellent article, compliments of Rob Davis, outlines the extreme's Canadian's face as we transition seasons. Over the next couple of weeks the odds of reaching 20°C quickly falls to zero at Vancouver International Airport.
A large part of our changing pattern that will play out over the next 6-9 days will in part be affected by strong typhoons churning thousands of kilometres away on the other side of the Pacific Ocean.
A weakening typhoon pummelling parts of Japan is forecasted to re-intensify as a powerful extra-tropical cyclone near the Aleutian Islands.
There is a fairly high correlation between recurving typhoons and the long-wave pattern downstream of the system. Often, this can create intense ridging and high pressure over Alaska and Western Canada, and can bring pronounced cold over eastern Canada.
As Typhoon Phanfone dissipates on Monday it will reform as an extremely potent extratropical cyclone (Sub 950 mb) with significant wave height over 12 metres south of the Bering Sea.
Notably, the maximum wave height one might encounter can be double the significant wave height, to close to 25 metres, (or six African elephants standing atop one another!). Eventually, this will bring strong surf to the BC coast by next weekend.
Model depiction of possible wave heights Wednesday evening:
How does this affect the weather in North America though? Chris. St. Clair from TWN goes into some detail about our upcoming pattern here, and conveys the next 5-7 day pattern across North America.
Essentially, a battle ground will set-up over North America with some locations seeing sunny, unseasonably warm conditions, while other locations will plunge into cooler temperatures as the recurving typhoons work to amplify our jet stream. The 500 mb height contours have the greatest amount of spread in southern BC, as shown below. The further the 582 dm height heads north, the warmer and drier the conditions should be over the Lower Mainland.
For another example, we'll take a look at individual ensemble members (12 and 13) of the Canadian model, which paints two very different possible solutions for Thanksgiving, especially along the West Coast. Shall we flip a coin, Van?
It's very rare that the North American Ensemble Forecast system produces such drastic changes in one short run - The evidence is quite obvious below:
The long-wave pattern has taken an abrupt shift west, and a once 90% chance of above normal temperatures for Southern BC has readily evaporated. Heck, we might even have a chance of seeing below normal temperatures for the interior of BC!
The Canadian control model picked up this BC trough pattern for early next week on Saturday morning with other global and control model following suit.
Unfortunately, I must agree with the very latest model guidance, and Vancouver, you are likely to see a showery, unsettled pattern for your holiday Monday next week.
Sorry about that, Van. I would really prefer to be wrong about this.
Next week, I will be discussing how early the Vancouver area might see snowfall as I dissect an atypical early-season event from the 1980's. See you then!