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A direct discharge of Arctic air will take aim at the Canadian Prairies and far northern United States Plains late this week into the weekend as a massive ridge of high pressure forms over Alaska.
Temperatures likely to average anywhere from 5 to 14 degrees Celsius below normal over the Prairies late this week into the first half of the weekend.
I also expect some accumulating snow across the western half of Alberta Wednesday night into Thursday as a cold, upslope flow takes hold with a strong high building in from the north. People may see accumulating snow in Calgary.
Temperatures will likely remain well below normal across the Prairies over the next two weeks. The large trough associated with this cold air will gradually shift eastward during October which will lead to a cooldown in the East while BC turns warm and dry.
The GFS and latest European model now have major differences with the upper-level jet stream pattern around Oct. 4-5 with the GFS showing a strong ridge in the East, while the European has the ridge out over the central U.S. Plains with a weak trough in the East. At this time, I would lean toward the European model since it has been more consistent. Regardless, I would be careful to rush any chilly air too far to the east over the next few weeks.
In the meantime, a strong cold front is expected to trigger a line of locally severe thunderstorms over extreme eastern Ontario and southern Quebec. Main threats will be straight-line wind damage and intense downpours.
My latest long range projections based on models (Euro/CFSv2) and teleconnections/current observations.
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A drier and milder pattern for the West while the East experiences real fall.
Major shift in the weather pattern on the way.
Extreme weather pattern across North America to persist into next week.
Plenty of cold for the Prairies and more snow as well.
Coldest air will be directed into the Prairies over the next 1-2 weeks.
Chilly air to expand eastward as we head into October.