Multi-day severe weather outbreak ahead of SK/MB/ON

An outbreak of severe weather is expected across the Prairie Provinces starting this evening across Saskatchewan, spreading overnight across Southern Manitoba and again for Southeastern Manitoba and Northwestern Ontario on Wednesday afternoon.

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Tuesday June 8, 2021

Threat level: HIGH

Confidence: MODERATE (based on model agreements)

Expected hazards: DAMAGING WINDS // A QLCS-TYPE TORNADO OR TWO POSSIBLE (across Saskatchewan only)

Locations impacted: Southern Saskatchewan and Southern Manitoba

Timing: 7pm CDT to 3am CDT

Expected watch(s): tornado watches across Southern Saskatchewan & severe thunderstorm watches for Southern Manitoba

Severe weather outlook issued by NZP at 9am CDT and valid for today (June 8, 2021). Warm front (red), dryline (brown) and trough (orange).

Discussion: a low pressure will deepen across Montana dragging a warm front, becoming stationary, across North Dakota a dryline across the High Plains of the U.S. and a trough of low pressure across Saskatchewan. The interaction with the low pressure, the warm front and the trough will trigger storms near Grasslands National Park in Saskatchewan. With lack of better thermodynamics, a wind-driven severe weather outbreak is likely as an eastern-propagating MCS this evening across Southern SK and into Southern MB in the overnight hours, possibly making it all the way to Winnipeg in the early morning hours. Below is an HRRR depiction of a massice MCS moving across SE Saskatchewan overnight.

HRRR simulated reflectivity for 1am CDT.

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Wednesday June 9, 2021

Threat level: HIGH

Confidence: MODERATE (based on model agreements)

Expected hazards: VERY LARGE HAIL // DAMAGING WINDS // A FEW TORNADOES

Locations impacted: Southeast Manitoba & Northwestern Ontario

Timing: 5pm CDT to 10pm CDT

Expected watch(s): severe thunderstorm watches for Manitoba and tornado watches for NW Ontario

Severe weather outlook issued by NZP at 10am CDT and valid for tomorrow (June 9, 2021). Warm front (red) and cold front (blue).

Discussion: similar to the previous day, the low pressure and associated fronts will make their way east. Storms should initiate across SE Manitoba with the interaction of the low pressure, warm front and trough of low pressure. Storms that develop across this environment will have supercell structures with all hazards possible before a possible merger into another eastward-propagating MCS moving across NW Ontario. The intensity of the storms will depend on airmass recovery in the wake of the morning MCS. Given sufficient destabilization across SE MB/NW ON, large MLCAPE values, veering profiles and elongated hodographs, a severe weather outbreak is expected to continue on Wednesday. Unlike the previous day, tornadoes will be possible, especially near the ON/MB border near the Trans-Canada Highway, where the tornado risk has been outlined.

NAM 3km simulated reflectivity for 6pm CDT tomorrow.

Please keep an eye on the latest watches/warnings issued by Environment Canada by going here: https://weather.gc.ca/warnings/index_e.html