A Big Shift in the Weather

A big change in the weather is on the way as a major low pressure system moving across Manitoba through the second half of the week shifts the province into an unsettled and significantly cooler pattern.

Wednesday
30°C / 19°C
Sunny, hot and muggy

Thursday
24°C / 16°C
Morning (thunder)showers then mixed skies with a chance of showers redeveloping

Friday
23°C / 13°C
Mixed skies; slight chance of scattered showers

Today will be another gorgeous, warm day with plenty of sunshine and highs in the upper 20’s, perhaps even reaching the 30°C mark. With the developing low pressure system still to our west in Saskatchewan, a broad southerly flow will continue to draw heat northward and trap moisture near the surface. The result will be a fairly humid day that ends up feeling closer to the mid-to-high 30’s instead of “just” the high 20’s. It will also be one of the breezier days in a while with winds picking up to around 30km/h this afternoon. Some cloud cover will likely begin working its way into the Red River Valley through the afternoon or early evening as the incoming low pressure system tracks eastwards.

Some showers or thunderstorms will develop through southeastern Saskatchewan and North Dakota and lift northeastwards through the night. Whether or not they move into the Red River Valley is another question altogether. The entire system is moving a little slow and there is uncertainty as to whether the showers will be extensive or tied closely to the surface low. That said, I think that there’s a chance for showers or thunderstorms in Winnipeg through the second half of the overnight period.

Thursday: Likely Wet

Tomorrow will likely start off with some rainy weather in Winnipeg as some rain or thunderstorms move through the city. The potential for a fair amount of rain exists, with models forecasting anywhere from almost nothing to nearly 50mm of rain. While nothing is entirely possible – models can handle precipitation that develops during the night-time in summer poorly – so is the other extreme; with precipitable water values forecast to reach nearly 2 inches (50mm), that same amount of rain is possible if the convective system happens to be a slow-moving one. What happens will depend highly on what develops tonight, so we’ll be keeping a close eye on it.

RDPS forecast precipitation amounts for the daytime on Thursday indicate upwards of 40mm in Winnipeg
RDPS forecast precipitation amounts for the daytime on Thursday indicate upwards of 40mm in Winnipeg

The rain will push off to the northeast through the morning and leave us with mixed skies and a chance of some shower activity redeveloping in the afternoon. Winds will be fairly light as the temperature climbs to around 24°C.

Thursday night will be fairly cloudy with a chance of the odd shower as the temperature drops to around 16°C.

Friday: Continued Cooling

Friday will offer a brief reprieve from the unsettled weather with mixed skies gradually becoming more cloudy as the day wears on and a high near 23°C with a northeasterly wind. There will be a slight chance of some scattered afternoon showers, but their impact looks to be minimal if they develop.

Friday night will see temperatures dropping to around 13°C with a decent chance at seeing more shower or thunderstorm activity developing over the Red River Valley as another impulse begins lifting northwards out of North Dakota into Manitoba.

Big Cool-Down in Store for Southern Manitoba

We’re in store for much cooler weather over beginning this weekend persisting through next week as a large upper-level cold trough develops over the Prairies as another system pushes through Manitoba bringing a renewed chance for rain.

The 6-10 day temperature outlook issued by the CPC in the United States shows a high probability of below-normal temperatures.
The 6–10 day temperature outlook issued by the CPC in the United States shows a high probability of below-normal temperatures.

This upper-level cold trough will shunt the jet stream further south and allow much cooler air to spill southwards out of the Arctic. This will drop our daytime highs into the teens and provide some distinctly fall-like weather. There’s some uncertainty to how cold it will get, but it seems fairly safe to say that daytime highs in the mid-teens are likely. Overnight lows won’t be too horrendous, generally dropping into the 5–8°C range.

Cooling Trend Brings More Unsettled Weather

The system that brought severe thunderstorms to the Interlake and southwestern Manitoba will bring a huge shift in the weather pattern over the next couple days as it moves over Hudson Bay and stalls, setting up an extremely abnormal pattern for July that will see cool Arctic air spilling southwards unhindered. In the process another cold front will slump through Southern Manitoba bringing another day of unsettled weather on Saturday.

Friday
25°C / 15°C
Becoming mainly sunny.

Saturday
26°C / 11°C
Showers or thunderstorms likely.

Sunday
19°C / 9°C
Mainly cloudy.

Today will be a fairly nice day all things considered. Winds will be out of the west to northwest at 20-30km/h as temperatures climb into the mid-20’s. No precipitation is expected today. Temperatures will remain somewhat mild tonight, dropping only into the mid-teens.

The RDPS, among other models, is forecasting widespread shower activity in Southern Manitoba on Saturday.
The RDPS, among other models, is forecasting widespread shower activity in Southern Manitoba on Saturday.

Saturday will bring another bout of unsettled weather as a cold front slumps southward through the Interlake into the Red River Valley. Instability will build throughout the morning with showers and thunderstorms developing along the cold front by midday through the Interlake. The activity will slump southwards through the day, with showers and thunderstorms likely through the Red River Valley, particularly the northern & eastern halves.

Saturday is also the Morden triathlon. Conditions will be fairly pleasant, with temperatures around 15°C in early in the morning warming to around 24°C by lunch time. Winds will start the morning out of the southwest at around 15km/h and increase to 30km/h or so by midday. There will be a very slight chance of a shower beginning late in the morning and through the early afternoon, although precipitation is most likely to hold off until the cold front passes through the region late in the afternoon.

Sunday will mark our first day in a very unseasonably cold air mass. Most of Southern Manitoba will see a northwesterly wind at 30-40km/h. The high will only be around 19°C – some 7 or 8°C below normal. There will be a chance of showers on Sunday night while temperatures dip below the 10°C mark.

How Long Will The Cold Last?

The CPC is forecasting a 100% chance of below-normal temperatures for the Eastern US in the 6-10 day range.
The CPC is forecasting a 100% chance of below-normal temperatures for the Eastern US in the 6-10 day range.

There’s no question the incoming cold air is hugely abnormal for this time of year: 1000-500mb thicknesses[1] are expected to fall below 546dm through Northwestern Ontario into MN/WI/MI. These values are more appropriate for late in the fall than in the middle of July. Depending on exactly how deep this cold trough becomes, record low thicknesses for July may be set in those regions.

Here in Manitoba, we’ll avoid the core of the coldest air, but we’ll still be well below normal. Fortunately this setup doesn’t appear to want to remain locked in for very long. The cold trough is expected to push off to the east fairly quickly with warm air pushing back into the province by mid-week.

As the warm air pushes in, it actually looks like we may finally move into a warm and dry summer-like pattern. All long-range weather models are showing a nice dry spell developing from mid-week into next, with temperatures gradually warming up towards the 30°C by the end of the week!


  1. The 1000-500mb thickness is literally the distance between those two levels in the atmosphere. The colder the column of air is, the lower the thickness while the warmer the column is, the higher the thickness is.  ↩

Hot Weather Returns; Another Thunderstorm Risk

An upper ridge building into the eastern Prairies will bring the heat back, sending the temperatures back towards the 30°C mark.

Conditions will be beautiful – and very welcome to those sick of all the rain this summer – with plenty of sunshine through the second half of the week. A low pressure system will drag a trough across Southern Manitoba late Thursday into Friday morning, which will likely spark off another round of thunderstorm activity through the region.

Monday: Start the Warm-Up

Wednesday
24°C / 13°C
Mainly sunny

Today will be a beautiful day with light winds, mainly clear skies and a high near 24 or 25°C. The “significant” weather event of the day will be the passage of a ridge of high pressure which will be marked by a gradual transition of the winds from northerly to southerly, setting up the return flow of heat for the remainder of the week.

Thursday: Hot with Severe Thunderstorm Risk

Thursday
28°C / 19°C
Increasing cloud & breezy

UPDATE: Updated thunderstorm discussion is available in the comments, right here.

Things become more interesting on Thursday as a low pressure system tracking along the NWT/Nunavut border drags a secondary frontal wave across the southern Prairies. Temperatures will soar into the high 20’s across southern Manitoba on Thursday with a southerly wind at around 30km/h. Humidity will also build ahead of the approaching system with dewpoints rising into the mid-to-high teens by the end of the day.

Clouds will likely begin building into the Red River Valley through the afternoon, but no precipitation is expected until the overnight hours.

The GDPS precipitation forecast for Thursday night shows nocturnal thunderstorms across Southern Manitoba.
The GDPS precipitation forecast for Thursday night shows nocturnal thunderstorms across Southern Manitoba.

At this point, it’s too early to go into specifics, but even already it looks like there’s a slight chance of severe thunderstorms over western Manitoba on Thursday evening with all modes of severe weather possible.[1] The threat will continue eastwards overnight as the storms become elevated and continue on through the night. The southward extent of the storm activity is unclear now, but it seems that for Winnipeg and the Red River Valley, there’s a decent chance we’ll see thunderstorms overnight with greater likelihood northwards through the Interlake. These storms will also have the risk to be severe with large hail and strong winds.

Pleasant Friday

Friday
26°C / 14°C
Mainly sunny

Friday will find Winnipeg on the back-side of the system moving across the Prairies and will see quite pleasant conditions with a ridge of high pressure building in from the west. Temperatures will be pleasantly warm with highs near the mid-to-upper 20’s and light winds. Temperatures will drop into the mid-teens overnight.

Long-Range

Bad news everyone. Brace for the return of below normal. A prominent long-wave ridge is forecast to build up over western North America with a resultant long-wave trough developing over Hudson Bay into the Great Lakes.

The CPC 6-10 day temperature outlook shows below normal temperatures through Southern Manitoba.
The CPC 6-10 day temperature outlook shows below normal temperatures through Southern Manitoba.

This will set up a persistent northwesterly flow which will likely produce slightly below-normal temperatures.[2] The heat and main storm track will shunt southwards into the Northern & Central Plains, leaving us with just the odd system sliding southeastwards in the northwesterly flow.


  1. All modes being large hail, damaging wind gusts, torrential rain causing localized flash flooding and the risk of a tornado.  ↩
  2. Normal high temperatures in Winnipeg for early-to-mid July sit near 26°C.  ↩