United States

Significant Weather Event Potential for This Week

September 03, 2013; 4:01 PM

A quick breakdown at potential significant weather events for the rest of this week and into next week across Canada....

1. Fairly potent upper-level storm off the Pacific Northwest coast will drift inland over the next 48-72 hours. As this happens, the air mass over southwestern Canada will become increasingly unstable over the interior of southern BC. I expect isolated showers and thunderstorms across the region Wednesday afternoon with the potential for some severe storms over southeastern BC in the form of gusty winds and hail.

2. By Thursday, the main storm system and its associated moisture spreads up through southern BC and into extreme southwestern Alberta. Thunderstorms will be more widespread compared to Wednesday with the potential for some localized heavier rainfall. The main threat for severe thunderstorms will be close to the U.S. border from south-central BC to southwestern Alberta.

3. This same storm system will almost stall over south-central BC on Friday. This will produce a moist, upslope flow into the Rockies then the foothills of southwestern Alberta late in the day and through the evening with the potential for a heavy band of rain and thunderstorms. Heavier rain and storms could also spread into southwestern Saskatchewan Friday night. This is the type of setup that could produce localized flooding across southwestern Alberta, but not nearly to the extent of what we saw early in the summer.

4. As predicted last week, high pressure will build over the eastern Prairies later tonight. The combination of clear skies and light winds should allow temperatures to drop very quickly tonight. However, the air mass is just not cold or dry enough to support a widespread frost. Any frost that does occur will be in the northern end of Lake Winnipeg region and points north/northeast.

As this high pressure system shifts southeast Thursday it will open the door to another surge of heat (32 C or higher) into southeastern Alberta and southern Saskatchewan on Thursday before the storms cool things down for Friday.

GFS model projected temperature departures in degrees F for Thursday.

5. The polar vortex will sit over northern Quebec Wednesday and Wednesday night delivering the coolest air mass of the season to northern Ontario and much of Quebec through Thursday. Clouds and wind should prevent a widespread frost/freeze, but daytime temperatures will be well below normal.

This type of pattern will also force very moist, Atlantic air up from Nova Scotia into Newfoundland tonight through Wednesday with rainy and windy conditions.

Temperatures will rise rapidly across Ontario and Quebec by Friday as southwesterly winds take over.

The views expressed are those of the author and not necessarily those of AccuWeather, Inc. or AccuWeather.com