A large, slow-moving storm centered off the Pacific Northwest coast will track slowly eastward over the next couple of days as it brings heavy rain and/or severe thunderstorms from the Canadian Rockies to southern Manitoba.
The heaviest rainfall though Thursday will be along the foothills of southwestern Alberta, as easterly winds upslope (warm, moist air rises into the higher elevations then cools and condenses out as heavier rainfall) into the region creating a favorable setup for heavy rain, flash flooding and potential land slides.
Below is my latest thinking for rainfall potential for the entire event through Thursday.
Severe thunderstorms and possible tornadoes into this evening
Quite a setup is in place for severe weather from the southern half of Alberta and spreading east-southeast over the next couple of days.
The combination of the vigorous, mid-level storm system and warm, humid air getting drawn up from the southeast is a recipe for severe thunderstorms with large hail, damaging winds and even some tornadoes.
The map below shows the greatest threat area for severe thunderstorms through this evening. We have already seen some big storms over southeastern BC and into south-central Alberta this afternoon.
Wednesday severe weather threat
Looks like areas from extreme southeastern Alberta, just east of Lethbridge, including Medicine Hat, then into extreme southern Saskatchewan, including Swift Current, will have the greatest risk for damaging thunderstorms Wednesday afternoon and evening. The worst of the storms may end up just to the south of Regina Wednesday evening more toward the U.S. border.
Thursday severe weather threat
The threat area continues to shift eastward by Thursday. At this time, I favor extreme southeastern Saskatchewan, including the Estevan area on eastward into extreme southwest and south-central Manitoba Thursday afternoon and evening. Again, the greatest risk for damaging storms will be close to the U.S. border where the dewpoints may flirt with the 20 C mark. I also think there will be thunderstorms from Brandon to Winnipeg Thursday afternoon or evening, but that the threat for severe will be reduced as I think the storms will be more elevated, meaning there will be some cooler air closer to the surface. Elevated storms can still produce a lot of rain, lightning and hail, but the strong winds tend to stay above the surface.
Questions or comments? Feel free to post a comment below or you can interact with me on twitter @BrettAWX
You can also email me right here.
Forecast pattern clues through most of July.
Thunderstorms this weekend and a look at the long range.
Some new clues to the summer and fall season.
Amplified jet stream pattern will keep forecasters on their toes over the next week or so.
Weather pattern clues for the next several weeks.
A look back at May and the spring of 2016 in terms of temperature departures.