Summer finally arrives in Winnipeg this week with seasonal to above-seasonal temperatures in place right through the week.

An approaching low will spread heat and southerly winds of 20 to 30 km/h through the region. Much of the day will bring partly cloudy skies to the city as temperatures soar to a high near 29°C. Notably different from other warmth so far this year will be the humidity; by the afternoon, dew points will climb into the mid-teens. While it won’t feel humid per-say, it will be a noticeable difference from when temperatures reached 30°C last Thursday. The chance for thunderstorms will develop mid- to late afternoon and persist overnight as the low pressure centre approaches. Temperatures will stay warm on Tuesday night with a low near 18°C.

The low will move through the Red River Valley on Tuesday morning, bringing mixed skies northwesterly winds. By midday, the city will be under mixed to mainly sunny skies with northerly winds near 30 gusting 50 km/h. These northerly winds will clear the skies and usher in a drier air mass the afternoon. Temperatures should reach a high near 26°C midday then cool to around 21°C by the evening. Winds will ease in the evening and Winnipeg will have a pleasant night: clear skies, light winds, and a low near 12°C.

Wednesday will see a high pressure system pass by to the south. It should keep winds light with a few clouds through the day. Temperatures will be warm again, though, with a high near 27 or 28°C. Another low pressure system moving through Saskatchewan will lift a warm front northwards through the province overnight. As it moves through, it will bring a chance of showers and/or thunderstorms to Winnipeg overnight.

Technical Thunderstorm Discussion

There is a widespread thunderstorm threat over the southeastern Prairies today. Although many ingredients are in place, the overall situation is conditional. Going over the MIST ingredients:

• Moisture: Dew point values are forecast to rise into the mid-teens. There is a bit of uncertainty in this as dew points have been trending below model forecasts lately. That said, yesterday evening a pool of 15°C dew points was in place over western South Dakota. With the low-level jet continuing advection overnight, it seems likely that dew points should rise substantially towards forecasted values as the day progresses.
• Instability: These dew points are forecast to produce MLCAPE values between 1000 and 1500 J/kg over SE Saskatchewan and SW Manitoba this afternoon. This instability will spread eastwards into the Red River Valley this afternoon. The instability will continue overnight with forecast MUCAPE values near 1000 J/kg spreading into the southeastern corner of the province.
• Shear: Weak upper-level winds will limit shear in areas of greatest CAPE; only ~15 kt of 0-6 km bulk shear is forecast. Closer to the warm frontal boundary, strengthening upper-level winds increase the shear into the 30 to 35 kt range. Shear profiles are generally veering and would support primarily multicell thunderstorms.
• Trigger: The warm front will be the primary area of focus, but strong capping will likely delay initiation until evening. Broad destabilization over southwestern Manitoba as the low approaches may trigger surface-based convection, but the storms may struggle to organize due to the lower shear values and poor ventilation aloft.
  

The best chance for thunderstorms looks to be over western and southwestern Manitoba this afternoon. These thunderstorms may be with the potential for some marginally severe thunderstorms. Heading into the evening, some of the activity will spread into the Red River Valley. It will likely become less extensive as the night progresses. The threat for severe thunderstorms will diminish as the night goes on.

Long Range Outlook

After Wednesday, Winnipeg will see the warm weather continue, but skies will be variable as several disturbances make their way through. These will bring several chances for showers or thunderstorms to the city that may persist right into the weekend. At least overnight lows will stay in the low to mid-teens and those chilly mornings will be a memory of the past by then!

Today’s seasonal daytime high in Winnipeg is 22°C while the seasonal overnight low is 9°C.

Plenty more cloud cover lies ahead for Winnipeg this weekend as another warm front lifts northwards into the province and brings another round of showers and thunderstorms.

Winnipeg will see a bit of sunshine today with some breaks in the clouds expected throughout the day. Daytime highs will climb to a near-seasonal 19°C with light winds courtesy a ridge of high pressure moving through. Winnipeg will see a chance of showers later today as a weak upper-level disturbance rolls through. Temperatures will dip to a low near 8°C tonight with mixed skies continuing through the night.

On Saturday, a low pressure system over North Dakota will slowly lift a warm front north into the province. While Winnipeg may see a bit of sunshine in the morning, skies will cloud over through the day. Winds will be out of the northeast at 10 to 20 km/h. The cooler northeast winds will keep highs near-seasonal despite the advancing warm air.

Thunderstorm Threat Returns to Southern Manitoba Saturday Night

On Saturday night, a low pressure system will begin its trek from southwestern North Dakota towards Lake of the Woods. As it lifts northeastwards, elevated convection will once again fire north of the warm front, spreading showers and thunderstorms through a portion of southern Manitoba. This instability will persist into Sunday with the potential for showers and thunderstorms continuing through much of the day.

Given elevated convection 36+ hours out, there’s still a lot of the details that remain unclear. Early indications are that another round of severe thunderstorms will be possible; guidance suggests a fair amount of instability and strong shear to help the elevated convection organize. Right now it looks most likely over the southern Red River Valley into southeastern Manitoba. It’s early, though, and that could easily shift over the coming days. We’ll be keeping an eye on it. Given the extensive cloud cover and proximity of the warm front, Saturday night will remain mild with a low near 14°C in Winnipeg.

The instability continues through Sunday with a chance of showers or thunderstorms for Winnipeg. It won’t be an all-out rainy day and most of the precipitation should end up north of the city. Winds will be out of the northeast at 15-20 km/h for much of the day. As the low passes in the afternoon, winds will shift northerly to 30 gusting 50 km/h. Temperatures should reach a high near 18°C, but much warmer temperatures will be in place just to the southeast on the other side of the warm front where highs near 30°C are possible, so areas closer to the US border, particularly southeast of Winnipeg, will see much warmer highs. Given the large change in temperatures across the front, if its position ends up a bit further north then Winnipeg could see a much warmer high.¹

The cloud cover will remain as the precipitation moves off to the east on Sunday night. Temperatures will dip to a low near 9°C as cooler air pushes south behind the low.

Long Range Outlook

Monday will bring more cloud to Winnipeg with a slight chance of showers as a weak low pressure system moves through the region. Temperatures will be much cooler with a high in the low to mid-teens. The remainder of the week will bring mixed to cloudy skies and seasonal to slightly below-seasonal temperatures. Another batch of rain looks possible in the second half of the week. After a dry first two thirds of the year, it seems like Winnipeg may finally be beginning to catch up on its precipitation deficit!

Winnipeg’s seasonal daytime high is currently 18°C while the seasonal overnight low is 6°C.

1. That said, it’s not particularly common for warm air to push further north than expected at this time of year. ↩