Sweltering Heat Moves Into Manitoba

The coming days will be marked by a rare late-summer heat wave that will see hot and humid conditions moving into the Red River Valley, sending humidex values soaring towards the low 40’s. The hot weather will be relatively short-lived, though, as a cold front moving into the region on Friday will send temperatures back towards seasonal values alongside a returning chance for showers or thunderstorms.

Wednesday
32°C / 20°C
Sunny; hot and humid
Thursday
33°C / 22°C
Partly cloudy; hot and humid
Friday
27°C / 15°C
Increasing cloudiness with afternoon showers or thunderstorms likely

Today and tomorrow will both be swelteringly hot days with daytime high temperatures in the low 30’s throughout Winnipeg & the Red River Valley. Humidity will increase dramatically this morning as temperatures begin to warm and the boundary layer deepens and taps into a significantly more humid air mass that’s moved in aloft overnight. By mid-to-late morning, dewpoint values will have climbed into the high teens or low 20’s across the Red River Valley. Combining the high dewpoints with the hot daytime high temperatures, humidex values in the upper 30’s to low 40’s are expected. Environment Canada has issued a heat warning for Winnipeg as well as many other areas across Southern Manitoba including the southwestern corner, Red River Valley, and southeastern Manitoba. Thursday will be slightly warmer and more humid than today is as both the temperature and dewpoint are expected to climb another degree or two higher.

RDPS Forecast Humidex valid the afternoon of Thursday September 3, 2015
The RDPS is forecasting a large swath of humidex values over 40°C (orange) in Manitoba on Thursday afternoon.

With such substantial humidity in place, overnight lows both tonight and tomorrow night will be quite warm, bottoming out near the 20°C mark. Additionally, expect just slightly breezy winds out of the south.

Friday will bring increasing cloud through the day as a cold front approaches from the west. Temperatures should manage to climb into the upper 20’s before the cloud cover cuts off our daytime heating. At this point, it looks quite likely that a large are of showers and thunderstorms will work their way across the Red River Valley through the afternoon. Severe thunderstorm potential looks minimal at this time, but we’ll keep an eye out and issue and outlook if it seems like it might pose more of a threat. Temperatures will cool down into the mid-teens on Friday night with clearing skies.

Summer Isn’t Over Yet!

We’ll see more summer-like weather this week in Winnipeg and across the Red River Valley as it continues to feel more like July than the beginning of September.

A shortwave trough (white dashed line) will pass through southern Manitoba on Monday, bringing clouds and a risk of thunderstorms.
A shortwave trough (white dashed line) will pass through southern Manitoba on Monday, bringing clouds and a risk of thunderstorms.
Monday
27°C / 12°C
Mainly cloudy, then clearing
Tuesday
29°C / 17°C
Mainly sunny
Wednesday
31°C / 20°C
Mainly sunny

Monday

Today will start out mainly cloudy as a potent upper disturbance moves through southern Manitoba. This disturbance may trigger some thunderstorms early on Monday morning, some of which could impact Winnipeg and the Red River Valley. Once the disturbance moves through, skies should clear, likely at some point in the afternoon. Temperatures will be in the mid to upper twenties with the wind becoming westerly due to the passage of this system.

Tuesday

Tuesday will be a nice day, as temperatures climb into the upper twenties under mainly sunny skies. Winds will be relatively light and from the south. No precipitation is expected on Tuesday, although some storms may develop overnight into Wednesday.

Wednesday

Like Monday, we may see some morning thunderstorms on Wednesday. A strong push of moisture from the south may help to trigger these storms. Should storms develop, they could be severe, but this forecast is still a few days away, so it could change. Besides the risk of storms, Wednesday will be hot and humid, with temperatures near 30C and breezy south winds.

Long Range

The long range forecast shows us cooling down after this week. Once a strong system passes through on Thursday temperatures will drop down to more seasonal values near 20C. Enjoy this little blast of heat while it lasts, it could be one of our last warm spells this year!

Erika: Yet Another Tropical Disturbance in the Atlantic

Yet another tropical disturbance has developed over the Atlantic this week thanks to another mid-level wave traversing off the coast of Africa westwards over the Atlantic. It’s currently impacting the Dominican Republic and is forecast to head west-northwest towards the southeastern United States.

Erika, which formed near the Cape Verde Islands, was centered near the southwest corner of the Dominican Republic as of Friday night bearing sustained winds of 75km/h and a rather unimpressive pressure of 1000mb. The tropical disturbance has struggled mightily at getting even somewhat organized over ocean waters; dry air and strong shear were both contributing factors to this. Erika is expected to continue experiencing problems organizing in the near future due to the strong wind shear in place, as well as a new concern – the rugged islands of Hispaniola.

IR satellite image of Erika on Friday night. Erika looks rather disorganized due to relatively strong shear present, but could still bring heavy rainfall to some Caribbean Islands. (Source: NHC)
IR satellite image of Erika on Friday night. Erika looks rather disorganized due to relatively strong shear present, but could still bring heavy rainfall to some Caribbean Islands. (Source: NHC)

The heavy rains that accompany this tropical disturbance are not to be underestimated, however. Heavy rainfall in the order of 100mm to 150mm, as high as 250mm locally, is expected to fall across both the Dominican Republic and its neighbouring country, Haiti. There have already been 20 confirmed deaths associated with Erika from the island of Dominica (located in the Lesser Antilles), and three dozen more residents are still missing. In consequence, this tropical storm has been the deadliest natural disaster for the country since 1979.

The future of Erika remains uncertain at this point. Most models show Erika as weakening over the Caribbean islands (due to the shear/terrain problems discussed), then emerging over waters off of the western coast of Florida as a weak tropical storm. Overall, it’s unlikely that Erika will become anything more than a tropical storm that is just a rain-maker for southeast US.

In other news, it had been the year of the hurricane in the Eastern Pacific near the Hawaiian Islands. Several hurricanes have brushed by Hawaii already this year – an unusual occurrence. Yet another is on its way in the coming week. Hurricane Ignacio (category one) is expected to pass close to Hawaii. What remains to be seen is how close – Hawaii can at least expect high surf and heavy rainfall from the outer bands of Ignacio on Monday, but there is still some uncertainty on strength of the winds which depends on how close Ignacio comes. Another hurricane in the Eastern Pacific is churning; Jimena, is a high-end category four but is not expected to have any impact to land in the near future.

Unsettled Friday Leads Into A Hot Weekend

Notably warm and humid weather in place over Southern Manitoba today will bring a threat for severe thunderstorm activity across the region as a shortwave trundles through. An upper-level ridge will then begin to rebound back into the Southern Prairies in response to a digging trough off the western coast of North America, bringing even warmer air into the region thanks to the resultant southwesterly flow aloft that will develop.

Friday
29°C / 17°C
Mixed skies with risk of a thunderstorm
Saturday
30°C / 20°C
Mainly sunny; hot and humid
Sunday
32°C / 19°C
A few clouds; hot and humid

Friday: Thunderstorms Possible Midday

A weak mid-level shortwave trundling across the region will bring a risk of thunderstorms to Winnipeg & the Red River Valley today[1] as warm and humid weather meets the colder air associated with the shortwave. As always, using our MIST principles:

  • Moisture: Adequate. Moderate moisture will be in place both at the surface and through the lower levels of the atmosphere as deep-layer moisture continues to build into the region.
  • Instability: Favourable. With both thunderstorm possibilities, both elevated and surface-based, enough instability will be in place. Surface-based convection would have greater potential to be severe, however it will rely on strong surface heating with mainly sunny skies until the shortwave arrives, which could be in question depending on what sort of nocturnal convection develops.[2] If it does end up cloudy, strong mid-level lapse rates associated with the shortwave should be enough to sustain showers or thunderstorms as it heads eastwards. All said, storms should have around 1000–2000J/kg of CAPE to work with, depending on their exact timing and where they’re based.
  • Shear looks quite good with around 35kt of 0–6km bulk shear and gently looping hodographs. Low-level winds are weak enough that tornado activity doesn’t look like a particular threat, but the directional shear is favourable for the organization of supercell thunderstorms.
  • Trigger: The shortwave moving through coupled with a weak surface trough will provide the convergence and trigger for convective initiation.
AWM Day 1 Convective Outlook
A slight risk of severe thunderstorms exists in the Red River Valley and southeastern Manitoba today.

All things considered, it’s likely that we’ll see some activity at some point today. The primary threats with today’s thunderstorms will be large hail and strong winds. Storm motions will generally be towards the southeast. Later in the day, a more organized heavy rainfall threat may develop with any storms still ongoing.

Those things aside, it will be quite a nice day. Temperatures will climb to around 28 or 29°C with a few clouds through the day. The humidity will begin to be more noticeable as dewpoints climb into the high teens by the afternoon ahead of the weak surface trough/low moving through. Winds will remain light.

Things clear out tonight with the humidity remaining in place and temperatures dipping down to about 17°C.

Hot & Humid Weekend Ahead

Temperatures will soar this weekend as warmer air moves into the region and sends daytime highs to 30°C or higher. Saturday will be a sunny day with a high around 30°C and dewpoint values in the high teens or low twenties making it feel more like the upper 30’s. Winds will be light. Expect a low near the 20°C mark on Saturday night.

Manitoba Health – Heat Alert Response System in Relation to the Heat Dial
This weekend could see provincial (pictured above) or federal responses to the heat and humidity over the region.

Sunday will see the daytime high climb even higher, most likely towards the 32 or 33°C mark as breezy southerly winds develop ahead of a developing low pressure trough. The humidity will remain in place with dewpoints in the high teens or low 20’s, making it feel more like the upper 30’s. There’s a slight chance we may see humidex values hit 40 on Sunday, which is Environment Canada’s criteria for a heat warning. That said, both Saturday and Sunday will likely qualify for the Province of Manitoba’s Heat Advisory and Response Pre-Alert which requires a humidex of 37 or higher.

There appears to be a slight chance late Sunday night or early Monday morning for some showers or thunderstorms to move through the area, but it looks very conditional at this point and it’s far to early to say much about it. We’ll put an update here early Sunday afternoon regarding the precipitation potential for Sunday night. Temperatures will likely only drop to around 19°C on Sunday night, however.

Long Term: Slight Cool-Down to Start Next Week

Looking ahead, it seems like we’ll see a slight cool-down next week as a frontal boundary stalls out over the region and brings a chance for multiple bouts of unsettled weather through the first half of the week. We’ll have more details about that bright and early Monday morning!


  1. Exactly when depends on the timing which will be affected by how much and what type of elevated convection developed with this feature overnight in Saskatchewan.  ↩
  2. If the nocturnal convection is in the right spot or strong enough, our sunshine could be replaced by cloud cover instead, dramatically limiting surface heating.  ↩