An energetic and dynamic weather system lifting through the Prairies will bring hot and humid weather to Winnipeg this weekend. As it passes through on Sunday, severe thunderstorms will be possible across the region.

Now that the morning fog and stratus has burnt away, it will get cooking over the Red River Valley. Temperatures will climb close to 30 °C with dew points close to 20 °C making it feel like the upper 30s through the afternoon.

Heading into the night, a low pressure centre will develop over southern Alberta and begin moving northeast. As it forms, it will begin to lift a warm front northwards out of the United States. This will bring partly cloudy conditions to the region overnight with strengthening southerly winds. Winds in Winnipeg will likely reach around 20 km/h by early Saturday morning, then quickly strengthen into the 30 to 40 km/h range as it warms up.

Saturday will bring mixed skies to Winnipeg with a high in the low 30s. Dew point values should sit in the high teens, though an axis of ≥ 20 °C dew points is forecast to lie immediately west of the Red River Valley. This again will result in humidex values in the upper 30s through much of Saturday.

It will be a hot, muggy night on Saturday night with overnight lows dipping only into the low 20s. The breezy southerly winds should continue through the night under partly cloudy skies.

Severe Thunderstorm Threat Develops on Sunday

The system moving through the Prairies, in addition to the heat and humidity here, will bring multiple rounds of potentially severe thunderstorms to the broader region. Severe thunderstorms are possible this afternoon over southwestern Saskatchewan; these storms will blossom into an area of showers and thunderstorms that track northeast across southern Saskatchewan overnight. On Saturday, another round of severe thunderstorms are possible beginning near the Manitoba/Saskatchewan border in the afternoon and spreading northeast across the Interlake through the night. Much of this activity is expected to stay north of the Trans-Canada Highway corridor in the Red River Valley, but isolated thunderstorms look possible in SW Manitoba.

By Sunday, though, it becomes the Red River Valley’s turn for thunderstorm activity. Sunday will likely be the warmest, muggiest day of the three with highs in the low 30s and dew points climbing into the low 20s, making it feel a lot closer to 40. The southerly winds will weaken in the afternoon as a warm-sector trough moves into the region.

For the enthusiasts out there: both the dynamic and thermodynamic setup for Sunday points towards a potent thunderstorm risk. The heat and humidity will drive MLCAPE values to over 2,500 J/kg, while late the day the right entrance to a 50 knot jet streak at H500 slides over the region. Surface winds ahead of the warm-sector trough are solid at 15 knots out of the SSE, but winds become weak and disorganized between the trough and the cold front. Bulk shear values are roughly 30 to 35 knots. MLLCL values are forecast to be moderate, roughly around 3,000 feet. Lastly, PWAT values will climb above 45 mm with Bunker storm motion values around 15 to 20 knots out of southwest.

The result of all that is that there is a potent thunderstorm risk that will develop on Sunday afternoon. Either the warm-sector trough or approaching cold front could be drivers for initiation, and both will be capable of producing dangerous thunderstorms capable of producing all modes of severe weather: very large and damaging hail, wind gusts of 90 to 120 km/h or higher, tornadoes, and torrential downpours capable of localized flash flooding.

All storms will have a roughly equal chance of producing damaging hail or wind gusts. There is a non-zero tornado threat across the region, though it will likely be maximized south of Winnipeg; a weak low centre is forecast to develop over northwestern North Dakota and weaken as it tracks northeast; if it holds together it could result in a stronger, more backed surface flow towards the southwestern Red River Valley that could enhance the tornado risk. Every thunderstorm will produce very heavy rainfall, but relatively high storm motions will likely limit the amount of rain a single storm gives to any one place. Widespread amounts of 20 to 50 mm are possible with the thunderstorm activity. If an area happens to have multiple thunderstorms pass over them, or a storm lingers for a longer period, then accumulations of 50 to 125 mm will be possible.

The thunderstorm activity will track east into the evening, pushed along by an advancing cold front moving through the region. Temperatures will head back down into the upper teens with a moderate northwest wind overnight.

Long Range Outlook

Next week will be an unsettled one for the region with seasonal temperatures. Monday should be pleasant, then cloud and showers will be possible on Tuesday as the region is clipped by a system moving through the Dakotas.

Showers and thunderstorms will again be possible on Wednesday evening through Thursday as another low pushes into the Prairies.

And that’s it for today! Stay safe in the heat, enjoy what you can, and make sure to check on anyone you know who’s more vulnerable (especially on Saturday night).

Be sure to stay tuned for any alerts issued by the MSC in the days to come.

Today’s seasonal daytime high in Winnipeg is 24 °C while the seasonal overnight low is 11 °C.