Weather Roller Coaster Ramps Up For The Weekend

A wild rollercoaster of weather conditions begins today as a fairly potent weather system develops today, rocketing temperatures close to the 30°C mark before things take a turn for the worse as a stormy transition sends daytime highs struggling into the low teens by the end of the weekend.

Friday: Another Beautiful Summer Day, Stormy End?

Today will be a gorgeous day as warm air surging northwards ahead of a developing low pressure system in the Northern Plains of the United States.  Temperatures will climb into the upper 20’s this afternoon under fairly sunny skies. Some cloud cover will start working into the region in the afternoon alongside a slight chance of showers as a weak mid-level disturbance rolls through. In the evening, a low-level jet (LLJ) begins to intensify as the low pressure system deepens and brings more lift into the region, spreading more cloud into the region.

850mb RDPS Temperature Forecast with Fronts & Low Level Jet Annotations
The RDPS is showing a warm front at 850mb just north of Winnipeg near midnight tonight. The LLJ is represented by the blue arrows and will be the trigger for thunderstorm activity tonight.

A round of thunderstorms is possible tonight along the nose of the LLJ.  The risk is somewhat conditional, dependent exactly how how much moisture is advected northwards within the LLJ. Assuming enough moisture is present to realize the instability, we head to MIST:

  • Moisture: This will be the most uncertain aspect of tonight’s thunderstorm potential.  Dewpoints at 850mb are forecast to be around 10°C, which should be enough to realize the elevated instability, however it’s a farily narrow ribbon, and if amounts are lacking a bit, convective initiation will struggle.
  • Instability: Fairly strong instability aloft will be present.  Models suggest mid-level (700 – 500mb) lapse rates of 7–8°C/km this evening, which would be considered quite strong.  If the expected moisture builds into the region, MUCAPE values of around 1000 J/kg should be realized.
  • Shear: The overall shear looks great, with widespread bulk shear values of 40–50kt expected over the Red River Valley this evening. The high bulk shear values are produced through a combination of strong velocity shear through the vertical coupled with large, looping hodographs indicative of favourable directional shear.
  • Trigger: Isentropic ascent of the LLJ as it overruns a warm front draped west-to-east along the international border coupled with falling heights ahead of the incoming upper-level low should provide a strong enough trigger to initiate convective activity.

All this combined means that there’s a fairly good chance of some thunderstorm activity through the Red River Valley this evening.  It likely won’t be severe; I think the higher threat for severe storms activity will be more in southwestern Manitoba where things will initiate earlier and rooted closer to the warm front.  That said, it certainly can’t be ruled out that there may be a rouge severe thunderstorm cell through the evening into the first half of the overnight period. Expect a low temperature near 17°C.

Mixed Bag On Saturday

There remains some uncertainty as to how Saturday will play out, but it seems quite probable that we’ll see some shower or thunderstorm activity through the day. There may be a few sunny breaks, but it should be cloudier than not through much of the day. If any rain manages to hold off until later in day, marginally severe thunderstorms could be possible in the Red River Valley, however it would be dependent on how much heating occurs (read: how sunny it manages to be). Even with decent heating shear looks marginal which will provide a barrier to significant thunderstorm development.

This comes with a caveat, however, as the forecast will be dependant on the timing of the cold frontal passage. With current best indications, there will be a slight risk of severe thunderstorms to the east of the Red River Valley on Saturday afternoon, however if the front slows down a little, that threat could shift westwards into the Red River Valley. We’ll take a closer look at it in an update tonight or tomorrow morning.

That said, temperatures will top out around 25°C with fairly light winds.

Saturday night will see the Red River Valley on the back side of the low and behind the cold front; colder air will begin pushing in alongside strengthening northerly winds. Expect a low near 13°C.

Miserable Sunday

Sunday will be a miserable day by any standard. Very cold air over the region—850mb temperatures are forecast to be a chilly 0–2°C—will keep our daytime highs to just the low teens. Very strong northerly winds will be in place over the region; sustained winds will likely reach 50–60km/h with gusts reaching as high as 80km/h or so. On top of all that, wrap-around precipitation will work it’s way across the Red River Valley, bringing more rain and/or showers to the region.

NAM Forecast 850mb Temperatures and Winds for Sunday Evening
The NAM is forecasting 850mb temperatures of 0-2°C and very strong northerly winds over the Red River Vallye on Sunday. Miserable.

To top it off, with lake temperatures near 21°C and 850mb temperatures forecast to be near 0°C, lake-effect or lake-enhanced rain/drizzle is probable in the lee of the lakes, persisting possibly into Monday morning.

The low temperature on Sunday night will be around 6 or 7°C.

Hopeful in the Long Range

The good news is that the long-range forecast looks good. Rather quickly behind the passage of this low, a broad upper-level ridge is forecast to begin building back into the Prairies. This will bring significantly warmer weather back to the region. Considering it’s still August and we’re talking about daytime highs in the low teens, a quick bounce back into the mid- to upper–20’s for daytime highs will be much appreciated.

Another Cold Snap in Southern Manitoba

Moderately miserable, categorically cold; the weather leading into this weekend will be fairly miserable as a large low pressure system moving through Ontario exerts its influence over southern Manitoba causing strong northwesterly winds as the coldest shot yet of Arctic air plunges southwards into the United States.

5°C / -1 to 2°C
Cloudy with showers. Flurries possible in the morning. Strong NW wind to 50km/h.

7°C / 0–2°C
Clearing except cloudy in the lee of the lakes

9°C / 3°C
Mixed skies with a slight chance of isolated showers or drizzle

Friday: A Miserable Fall Storm

The Red River Valley will be under the grip of a miserable fall storm lifting northwards through Northern Ontario today, driven by a massive push of cold Arctic air sweeping through Manitoba. We’ll see a very cold start to the morning with temperatures hovering around 2–3°C, strong northerly winds at 40–50km/h with gusts as high as 70–75km/h and a band of rain stretching north-south through the region. Embedded within the band will likely be some convection, significant since increased precipitation intensity could mean that in addition to the rain, we might see brief bursts of snow as well.

The precipitation should taper off by early afternoon, but we’ll still be left with a strong northerly wind and temperatures struggling to get to our high of 5°C. If the sun manages to poke out at all, we may eke out a 6°C for a high, but that looks quite unlikely.

The RDPS clearly shows Winnipeg nestled between two bands of lake-effect precipitation on Friday night.
The RDPS clearly shows Winnipeg nestled between two bands of lake-effect precipitation on Friday night.

Winds will begin to taper off tonight to around 20km/h. Combined with the cold air, the lake-effect machine will likely start up again, producing lake-effect showers or snow through the overnight period across regions in the lee of the lakes. At this point it looks like Winnipeg will remain safely between the two bands of lake-effect precipitation. The overnight low will be anywhere from –1 to 2°C, depending on exactly how much cloud remains in the area. Here in Winnipeg we should end up on the colder end of things under clearing skies.

A Chilly Weekend

It will be a chilly weekend in Winnipeg with temperatures on Saturday and Sunday both climbing only into the mid-to-upper single digits. Saturday should be a fairly nice day with mainly sunny skies in Winnipeg, but just to our west and east, lake-effect cloud (and likely precipitation) will be ruining a few people’s day. Temperatures will dip to the 0 to 2°C range Saturday night with just a few clouds. Again, lake-effect cloud will be present in the lee of the lakes.

Sunday will bring mixed skies as the whole storm system begins backing into Northern Manitoba from Ontario. Rain or snow will push through Central Manitoba into the Interlake through the day, spreading cloud ahead of it. Winds don’t look too bad this time – only around 20–30km/h – and precipitation should hold off in Winnipeg until overnight. Temperatures will drop to around 3–4°C on Sunday night, heading into a cool and showery Monday.