A powerful low-pressure system pushing northwards out of the Dakotas that will bring copious amounts of rainfall to SE Saskatchewan and Western Manitoba will also bring a risk for thunderstorms, perhaps even an isolated severe thunderstorm, this evening in advance of an occluding cold front. This will mark the start of a somewhat dreary weekend for the Red River Valley that will be marked most notably by a wet & windy Saturday and a very cool, albeit sunny, Sunday.

Thunderstorms Possible Today

Friday

19°C / 12°C
Mainly cloudy. Chance of showers with the risk of a thunderstorm late in the day.

We’ll see a mainly cloudy day today with relatively nice temperatures as we sit in the warm sector of the low pressure system pushing into the province. Despite the cloudy weather, we should see temperatures climb to around 19–20°C for a high with south-easterly winds to around 30km/h.

We may see a shower early this morning as the warm front pushes through and brings us into the warmer air, although a majority of the activity will be off to our west. If anything manages to push into Winnipeg, it will be relatively short-lived. After that we’ll see no chance of precipitation until later in the afternoon or the evening as a cold front begins pushing into the Red River Valley from the south.[1]

While we sit under cloudy skies, this would be a good time to note that the weather to our west will be decidedly different. Rain will push in early this morning and spread NNE through the day, hitting areas west of the Red River Valley and Lake Manitoba the hardest. In total, anywhere from 35–75mm of rain is expected, with the lesser amounts closer to the Red River Valley and the higher amounts running along the Saskatchewan border then towards Lake Winnipegosis with enhanced precipitation near the Riding Mountains as upslope enhancement in the north-easterly winds amplifies the amount of rain. Environment Canada has rainfall warnings out for many regions in Western Manitoba, and you can check here to see if your region is covered by one and find additional details.

As the cold front approaches the Red River Valley this evening we’ll see considerable destabilization of the mid-levels coupled with an extremely strong 60–70kt 500mb jet beginning to poke it’s nose north of the border. The Red River Valley will lie in a fairly diffluent area aloft with strong convergence along the cold front as it pushes northwards. Limited surface moisture will constrain SBCAPE values to only a mere 400–500J/kg, but the extremely strong dynamics, in particular the strong directional and speed shear, may help promote the growth of strong-to-severe thunderstorms along/just ahead of the cold front.

This all is highly dependant on either enough destabilization occurring or enough convergence occurring along the cold front. At this point, I think that the southern Red River Valley will see the strongest storms with a lesser risk of strong storms further north here in Winnipeg. By the time the front reaches us, it seems like it will be a band showers and/or thunderstorms with less organization than when things initiate in the Dakotas. If any of the storms do become severe, the main threats will be large hail and strong winds. There will be a very small risk of a few weak tornadoes with these storms, but I believe that will be most likely in North Dakota with the odds diminishing fairly rapidly as you push northwards through the Red River Valley.

The showers/thunderstorms will push through overnight as we drop to a low of around 11 or 12°C.

Wet & Windy Saturday

Saturday

↘ 6°C / 2°C
Cloudy with showers. Windy. Temperature dropping through the day.

Saturday in Winnipeg will be marked by wet and windy weather as we move onto the back-side of the Colorado low and see some wrap-around rain and gusty northwesterly winds move in.

The rain will likely be somewhat showery in nature – in that we won’t see solid rain all day long – and there’s some uncertainty on how much we’ll see exactly, but around 5mm seems like a relatively safe bet at this point. If the system is a little faster than forecast we could end up with almost nothing as the rain would fall further north, and if it’s slower than forecast we could see closer to 10mm as we end up under the wrap-around rain for even longer.

The wind will be the main weather story though. Here in Winnipeg we’ll see winds 30–40km/h out of the northwest with gusts up to 60km/h, but it will be a significantly different story for those on the lakes. Winds over the lakes will increase to nearly 50–60km/h on Saturday with gusts as high as 90km/h, which will produce fairly sizeable waves. If you have a home or cottage on the southern or eastern shores of the lakes, you’ll want to make sure you make any preparations you might have to and prepare for some strong wave action and howling winds for Saturday and Saturday night.

With those strong winds will come falling temperatures; here in Winnipeg we’ll likely see temperatures fall to around 5 or 6°C by the end of the day as colder air pushes in on the back-side of the low. Skies will clear and winds will lighten overnight as we drop to around 2°C for our overnight low.

Sunny but Cool Sunday

Sunday

9°C / -2°C
Sunny. Cool.

Sunday will see the return of the sun, but the price we’ll pay is significantly cooler weather than we’ve been having over the past week. Daytime highs on Sunday will top out at only 9 or 10°C and it will be a slow climb to get there. Temperatures will likely drop well below 0°C on Sunday night with a hard frost likely as temperatures dip to around –2°C.

This will also mark the transition into a cooler pattern. Daytime highs will remain around 10°C through much of the week.