Southern Manitoba will see its first blast of fall-like weather as gusty northwesterly winds draw cool air southwards over the region. Fortunately, it doesn’t look like the cold weather is here to stay and seasonal temperatures are expected to return by week’s end.
Monday
15°C / 7°C
Mainly cloudy; windy and cool with lake-effect showers possible
Tuesday
19°C / 10°C
Mainly sunny
Wednesday
23°C / 15°C
Mainly sunny
Today will be an unwelcome day for late August as abnormally cold air will move into the province behind the low pressure system that brought 20–40mm of rain to Winnipeg & the Red River Valley Saturday night into Sunday morning. Brisk northwesterly winds to around 30–40km/h will usher in this cooler air and will restrain our daytime high to just the mid-teens. Additionally, the abnormally cool air aloft and favourable wind profiles will combine to produce lake-effect showers that will spread southeastwards towards Winnipeg.
Forecast 850mb temperatures for this afternoon show a trough of cold air anchored over Manitoba.
Given that, occasional showers are likely in Winnipeg although due to the nature of lake-effect precipitation[1] the precise wind direction will determine whether or not the showers find their way into Winnipeg or whether they end up just north or just south of the city.
The clouds will clear out tonight as temperatures drop to around 7°C.
Tuesday and Wednesday will trend towards seasonal weather. Winds will be relatively light both days while the Red River Valley enjoys mainly sunny skies. Temperatures tomorrow will climb into the high teens while highs on Wednesday will reach the low 20’s. Lows on Tuesday night will bottom out around 10°C while Wednesday night sees more seasonal lows in the mid-teens.
Seasonal End to the Week
Looking ahead to the second half of the week, summer weather returns in full swing. Temperatures heading through the end of the week will see daytime highs in the mid–20’s with overnight lows in the mid-teens. The weather looks fairly dry until Friday when a weak cold front pushing across the province brings the chance for some shower or thundershower activity.
Lake-effect precipitation extends in a very narrow band along the direction of the wind. ↩
Wildfires continue to be the story out west as large areas of not only western Canada, but also the western United States are experiencing tinder dry conditions. As explained in last week’s EIWN, these conditions are due to the persistent ridging that took place in most of July and early August over the region. The ridge brought limited precipitation and warm, dry air to the western half of North America. The Drought Index reveals this well, showing a large chunk of the western US under severe to exceptional drought.
The Drought Index for this week continues to show significant drought in the west. (Source: USDM)
California which has seen no reprieve from the drought and saw another large wildfire flare up this week near Yosemite National Park. The fire, which started on August 18 just to the north of Oakhurst, quickly grew into a large wildfire that was out of control. Numerous air tankers, as well as 1,300 firefighters on the ground, are actively fighting the blaze. Yesterday the crews were able to gain more control of the fire, which was 95% contained as of Friday night. The wildfire is expected to be under full control by the end of this weekend. Some 500 structures in the path of the wildfire were at risk of getting torched on Tuesday and about 1,000 people had to evacuate from Oakhurst. As of Friday most homes had been saved though, with only 47 structures destroyed by the fire. The wildfire burnt an area totaling 612 acres, a small fire compared to the China Nose Fire discussed in last week’s EIWN which reached 9,100 acres in size this past week.
Map of current wildfires that are burning throughout California, Yosemite fire identified by the arrow. (Source: CAL Fire)
The next chance for rain in drought-stricken parts of California looks to be Tuesday as a trough digs into California and brings with it a chance of showers, however, there is signficant uncertainty regarding the strength of the trough.
A major low pressure system developing in the United States and forecast to lift northwards into the Eastern Prairies through the weekend will bring generally unsettled weather ahead of a more cohesive area of precipitation that will move through on Saturday night.
Friday
22°C / 15°C
Mostly cloudy with a chance of scattered showers
Saturday
19°C / 15°C
Mostly cloudy
Sunday
23°C / 15°C
Rain ending in the morning; sunny breaks with a risk of strong-to-severe thunderstorms thereafter
Perhaps the single most important thing to keep in mind with today’s forecast is the fact that weather models have little consensus on what’s going to happen over the next few days other than the fact that there will be a large low pressure system that will impact an area somewhere between the Rocky Mountains and the Great Lakes.
That being said, it looks like the next several days will bring mixed weather to Winnipeg. Today will see a chance for scattered shower activity as a weak shortwave rolls across the Red River Valley, but nothing nearly as bad as what hit the city last night, where up to 80mm of rain fell in a rapid deluge through portions of the city that resulted in wide-spread flooding through the hardest hit areas.
Temperatures will climb to around 21 or 22°C this afternoon with a light wind out of the north. Tonight will be mainly cloudy with fairly light winds and a low near 15°C.
Saturday: The Low Approaches
Tomorrow will see mainly cloudy skies with a high of just 19 or 20°C. Winds will pick up out of the northeast to 30-40km/h as the main low pressure system for the weekend strengthens and lifts northwards through the Dakotas. By supper time, rain with the chance for embedded thunderstorms will spread through North Dakota into Southern Manitoba, reaching Winnipeg later in the evening.
The RDPS is forecasting an intense convective complex with substantial rainfall amounts on Saturday night. Who knows if it’s correct.
The rest of Saturday night will be quite rainy with 10-20mm of rain likely across most of Southern Manitoba with localized amounts in excess of 30-40mm due to embedded convection in the precipitation shield. Some models, such as the RDPS pictured above, want to produce upwards of 50-75mm of rain, although at this point that’s likely overdone and a symptom of what’s known as “convective feedback” in the model, something that ends up causing the model to produce too much precipitation when there is widespread convection occurring. Temperatures will drop to around 15°C again with winds out of the northeast at around 30km/h.
More Unsettled Weather on Sunday
The weather on Sunday will likely improve as the low pressure system lifts through the Red River Valley and pushes off to our northeast. Rain will taper off in the morning and Winnipeg will be left under mostly cloudy skies in what’s known as the “dry slot” — the area behind the cold front located between the frontal precipitation and wrap-around precipitation denoted by descending dry air aloft. The high will climb to around 22°C with some strong northeasterly winds becoming light in the afternoon.
Significant instability associated with the low pressure system will be in place, and even with temperatures climbing only into the low 20’s, it will be enough when coupled with the significant moisture in place to present a risk for strong-to-severe thunderstorms. We’ll have more information in the comments on Sunday.
Things will begin to clear out on Sunday night as the temperature drops to around 13°C.
Into next week looks fairly benign with temperatures gradually returning towards normal by week’s end. There will be a couple cool nights in the coming week with overnight lows dipping into the single-digits.
We’ll be keeping an eye on this system as it develops; slight alterations in the track of the system could dramatically impact forecasts, so if any changes are needed we’ll note them below in the comments. All in all it will be a mediocre weekend followed by an improving week.
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
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.
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.
