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In an update to the forecast that was posted yesterday evening, we have extended the boundaries of the Slight Risk region to include Calgary and the entire Highway 2 corridor south of the city. The combination of damaging wind gusts, large hail, and the possibility of an isolated tornado from today’s has resulted in the Slight Risk for this area, along with Lethbridge, Medicine Hat, and Drumheller.

Thunderstorms have already begun to develop in Montana, moving northward towards the border. They will start to cross into Alberta later this afternoon and early evening, spreading across Southern Alberta throughout the rest of the evening and overnight. It’s possible that the storms could become organized into a line that will push northeastward starting later in the evening which will impact a more widespread area than just isolated storms.

The main threat from these storms will be the hail, with up to toonie to timbit-size likely, as well as damaging wind gusts that could exceed 100km/h and even approach 130km/h. At this time, there does not appear to be too much of a flooding risk, with these storms expected to bring less than 50mm of rain over the span of a few hours. An isolated tornado can also not be completely ruled out.

Friday will be another hot day across Southern Alberta and along with that heat comes severe thunderstorms. A combination of damaging wind gusts, large hail, and the possibility of an isolated tornado means that there will be a Slight Risk in an area that includes Lethbridge, Medicine Hat and north towards Drumheller.

The storms will cross into Alberta from Montana in the south starting in the late afternoon and early evening, spreading across the region throughout the evening and overnight hours. It’s possible that the storms could become organized into a line that will push northeastward starting later in the evening that will impact a more widespread area than just isolated storms.

The main threat from these storms will be the hail, with up to toonie-size likely, as well as damaging wind gusts that could exceed 100km/h. At this time, there does not appear to be too much of a flooding risk, with these storms expected to bring less than 50mm of rain over the span of a few hours. An isolated tornado can also not be completely ruled out. The risk level could change with more data from short-range models so stay tuned for any updates to this forecast.