Tuesday, August 20th 2019, 7:00 am - A changeable pattern and lack of consistent heat leading up to Labour Day long weekend in Canada.
In early August I wrote an article discussing the different patterns that we expected during the upcoming month.
This included a pattern map (shown below) for the final two weeks of August, featuring a continuation of the cool pattern across the Prairies and a warmer pattern from the Great Lakes to Atlantic Canada.
Our national pattern at the beginning of this week has closely resembled the forecast. However, a rather changeable pattern is expected during the next two weeks and at times the pattern will strongly go against our original forecast.
A taste of early fall will spread into Ontario and Quebec later this week and then continue into Atlantic Canada for the weekend. Another shot of chilly weather is expected for the Great Lakes region later next week. Meanwhile, the Prairies will see a more changeable pattern, which will not be as cool as initially expected.
SO, WHAT HAPPENED TO THE LATE AUGUST FORECAST?
While there is always some uncertainty in long range pattern forecasts, the late August pattern has proven to be extra complicated due to two powerful typhoons in the western Pacific earlier in the month.
RARE SCENARIO: Twin typhoons target Asia
Typhoons in that part of the world have a major impact on the downstream jet stream pattern, and often our confidence in a long range pattern is higher when there is a typhoon in the mix. While the models typically fail to see how typhoons will impact the downstream pattern, the meteorology is understood well enough to correct the model errors.
However, earlier in August we had not one, but two powerful typhoons (Lekima and Krosa), simultaneously in the western Pacific Ocean. While the track of either one of these storms by itself could have had a predictable but unique impact on our weather pattern, having two storms simultaneously (each with a different impact on the pattern) greatly complicated the forecast.
To further complicate matters, typhoon Krosa stalled for several days and weakened as it made its trek north out of the tropics. This added to the uncertainty as to how the impacts of the two storms would interact with each other and influence the jet stream pattern across North America.
Initially it was thought that the weakened Krosa would not be able to break down the pattern that super typhoon Lekima helped to establish, but it is now clear that will not be the case. The pattern at the end of the week will indeed resemble what we would typically see six to ten days after a typhoon or tropical storm has tracked into western Japan with a trough in the jet stream digging into the Great Lakes region. British Columbia will have to wait until next week to see the warmer weather that is typically associated with this pattern.
WATCH BELOW: RECURVING TYPHOON PATTERN
The final week of August is too far the after the dissipation of both Lekima and Krosa to blame our weather pattern directly on the typhoons. However, it is clear that both storms have severely disrupted the jet stream pattern across the Northern Hemisphere with more chaos than normal in the pattern. As a result, forecast confidence in the details of the pattern for next week is lower than normal.
At this point though, we expect that we will continue to see a changeable pattern, especially from Alberta to Quebec, with a lack of consistent heat across this region. Atlantic Canada and B.C. have the best chance of seeing an extended period of above normal temperatures next week as we wrap up meteorological summer and head into the Labour Day long weekend.