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.

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.

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.

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.

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?

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!