Sweltering Summer Heat Will Bring Severe Thunderstorm Threat

Winnipeg’s hottest, most humid day of the year is on the way with humidex values forecast to climb over 40 on Saturday. A cold front will push across the province Saturday evening, bringing the risk of severe thunderstorms to the region.

An upper-level ridge building over the Prairies will spread a southerly flow over Manitoba today. Tapping into Gulf of Mexico moisture over the American Plains, this southerly flow will draw very humid conditions northwards into the Red River Valley for Saturday.

Before that happens, though, Winnipeg will see a breezy and warm summer day today. Under sunny skies, temperatures in Winnipeg will climb to a high near 29°C with a southerly wind increasing to around 30 km/h midday then closer to 40 km/h by the evening. Those winds will keep the boundary layer well mixed through the night and keep the overnight low mild; Winnipeg should see a low near 21°C.

An extremely humid air mass will build into southern Manitoba for Saturday.

If you have a sensitivity to heat, then Saturday will be bringing dangerously hot weather into the region. A strong southerly wind near 40 gusting 60 km/h will continue to tap into the humid air mass to the south, pushing dew points into the low 20s across southern Manitoba. The humid weather will combine with daytime highs in the mid-30s – Winnipeg should see a high near 34°C – to produce humidex near or over 40. Humidex values are forecast to be most stressful1 between around 1PM and 8PM.

Skies will remain fairly sunny until a cold front arrives in the afternoon, bringing with it the threat of [severe] thunderstorms. While it’s a bit early to say too much with regard to the overall threat posed to the region, it goes without saying that a cold front pushing through that hot and humid air mass will pose the threat for severe weather. With over 4000 J/kg of MLCAPE forecast alongside 35 to 45 kt of 0-6 km bulk shear, the cold front would favour the development of discrete supercell thunderstorms capable of all modes of severe weather (very large hail, damaging wind gusts, and tornadoes).

The hot and humid weather will create an extremely high energy environment capable of supporting severe thunderstorms.

The biggest unknown at this point is where exactly the thunderstorms will develop. A strong capping inversion should keep things quiet for most of the day, but thunderstorms will likely fire along the cold front early in the evening. Current forecasts place the cold front near or just east of the Red River near 6PM, making the threat conditional for the Red River Valley. Eastwards, towards the Whiteshell and the rest of southeastern Manitoba, the threat will be much greater.

Behind the cold front, westerly winds will begin to ease the humidity as the temperature heads to another mild low near 19°C.

Sunday will bring another sunny day to Winnipeg with northwesterly winds at 20 to 30 km/h and a high near 29°C. The dew point will continue to drop into the low teens, making for a much more comfortable day. Temperatures will drop to a low near 16°C on Sunday night under mainly clear skies.

Long Range Outlook

Next week looks like a prototypical July week: a fair amount of sunshine, plenty of warm days with daytime highs in the upper 20s, mild lows in the upper teens, and a chance for some showers or thunderstorms. The week looks great, but there is a chance that Winnipeg will see thunderstorms late Tuesday through the overnight.

Winnipeg’s seasonal daytime high is currently 26°C while the seasonal overnight low is 13°C.

  1. We identify stressful humidex values as those which exceed the body’s normal temperature of 37°C.




Unsettled Wednesday Gives Way to Sweltering Summer Heat

After an unsettled morning, Winnipeg will see calmer weather and warming temperatures as an upper ridge builds across the Prairies.

Winnipeg will be starting the day with some unsettled weather as a line of thunderstorms moves through the Red River Valley. The stormy weather should clear out a bit later in the morning, leaving behind mostly cloudy skies and humid conditions. Dew points near 20°C will make temperatures in the low 20s feel more like 30 this morning. A cold front will pass through near lunch, bringing westerly winds to around 30 km/h. Along with the wind, markedly drier air will move into the the Red River Valley. Thanks to that, Winnipeg’s high near 25°C should feel comfortable by mid-afternoon. Under clear skies and a light west wind, Winnipeg will head to a low near 15°C tonight.

Conditions will settle quickly in the wake of Wednesday’s cold front. Hot on its heels, an upper-level ridge will begin building into the Prairies and bring sunny skies and increasingly warm weather. Winnipeg will see mainly sunny skies on Thursday with a seasonal high near 25°C. Winds will remain out of the northwest at around 20 km/h.

A ridge of high pressure will move through on Thursday night, bringing light winds, clear skies, and a low near 15°C.

An upper-level ridge will begin building across the Prairies on Friday.

Friday will mark the start of the warm-up as a southerly return flow develops behind the high. Winds will be light out of the south with sunny skies and a high near 27°C with comfortable humidity. Warmer air will continue to build into the region on Friday night, resulting in a mild low near 19°C.

Long Range Outlook

The weekend will be a scorcher as heat and humidity surge northwards into the region. Saturday will see temperatures climb into the low 30’s with dew points climbing into the upper teens. Humidex values on Saturday will climb towards 40. With all the heat and humidity, it does look like there will be a chance for thunderstorms. A “cool” front sweeping across the province on Saturday evening will bring the threat of severe weather back to Winnipeg. Sunday will still be warm with a high of 28 or 29°C, but the humidity will be much lower making for a comfortable summer day.

The warm weather will continue into next week with daytime highs expected to remain in the upper 20s with overnight lows near 18 or 19°C.

Winnipeg’s seasonal daytime high is currently 25°C while the seasonal overnight low is 13°C.


Summer Heat On The Way

Winnipeg will see temperatures in the upper 20’s for much of the week as the season’s first humid spell builds into the region.

Temperatures will be hot in Winnipeg over the next three days. Daytime highs near 29°C will be in place through Wednesday and are about 7-8°C above seasonal. Overnight lows will rise dramatically over the next few days as southerly winds bring humidity northwards into the province.

This increase in humidity will be one of the most significant changes this week. For the past several weeks, dew point temperatures have remained at relatively low values. This week, dew points are forecast to rise into the low teens on Tuesday, then further into the upper-teens on Thursday. This will be the first occurrence of relatively humid conditions this year.

RDPS 2m Temperature Forecast valid 21Z Tuesday May 22, 2018
Temperatures across southern Manitoba will climb towards 30°C on Tuesday afternoon.

Besides warm, the next few days will be pleasant. Winds will be a bit breezy out of the south today at 20 to 30 km/h, then will ease to the 10 to 20 km/h range for Tuesday and Wednesday. Winnipeg will see sunny skies today, but the region will see a bit more cloud with mixed skies on Tuesday. On Wednesday, Winnipeg should see partly cloudy skies. The southern Red River Valley will see more cloud as it spreads out of North Dakota ahead of a low pressure system moving towards the region.

Long Range Outlook

More extensive cloud cover will build into the Red River Valley on Thursday as a low pressure system moves into the region. This disturbance will bring a good chance of showers or thunderstorms Thursday night through Friday. A cold front looks to sweep through late Friday, beginning to clear the cloud and humidity out of the region.

The weekend is looking pretty great with seasonably warm highs in the mid- to upper-20’s and plenty of sunshine.

Winnipeg’s seasonal daytime high is currently 21°C while the seasonal overnight low is 7°C.

The Heat Is On; Thunderstorms Possible Saturday

While July has been relatively pleasant, temperatures have [somewhat surprisingly] been largely below seasonal for much of the month. That’s all about to change as significant heat builds across the region to round out the month.

A developing southerly wind of 20-30 km/h this morning will draw warmer air northwards out of the United States and help push daytime highs up to around the 30°C mark. Skies will remain mainly sunny and humidity in the mid-teens should keep things feeling relatively comfortable. Expect lows to fall to around the 19°C mark tonight with winds continuing out of the south and partly cloudy skies.

An upper ridge in place over Southern Manitoba today will bring warm temperatures to the region.

Saturday will see a cold front slowly sweeping across the province, bringing with it a severe thunderstorm risk. Before that, though, there will be a hot summer day on tap with highs once again near the 30°C mark under mixed skies. With the southerly winds slowly diminishing and dew points rising to around 19 or 20°C, it will end up feeling quite humid in the afternoon. The cold front will progress eastwards through the day, reaching the Red River Valley mid- to late-afternoon. As it pushes into the valley, it will bring with it the risk of severe thunderstorms.

Going over the MIST ingredients:

  • Moisture: Low-level moisture will be plentiful with surface dew points climbing towards the 20°C mark and with deep moisture extending towards 850 mb.
  • Instability: Slight to moderate instability will be in place. Mid-level lapse rates leave a bit to be desired with expected values only around 6-7°C/km, but this is somewhat offset by the substantial latent heat available through surface moisture. Depending on the exact orientation of this system, the heights may be rising as the front stalls, which would work against thunderstorm development.
  • Shear: Bulk shear values around 25-30 kt will be in place which is on the lower end of values. Low-level shear will likely be weak and mid-level shear largely unidirectional.
  • Trigger: The cold front will slowly slump southeastwards, gradually slowing into the evening hours.

The primary threats with any storms that develop will be large hail and damaging winds, although with dew points so high, torrential rain is likely as well. They would move southeastwards through the Red River Valley. The biggest question will be whether or not storms actually develop. The threat will exist generally around the Trans-Canada Highway corridor and south, but we’ll provide an update on Saturday with a new look at the day’s potential.

A cold front will be in place across Southern Manitoba on Saturday afternoon.

The thunderstorm threat will diminish before midnight and temperatures will then drop to a low near 17°C under clearing skies.

Sunday will be another hot day with a high near 31°C but more comfortable humidity as the dew point drops back towards the mid-teens. Skies will be partly cloudy and winds will be light out of the east. Winds will shift out of the south on Sunday night and increase to 15-25 km/h, keeping temperatures fairly warm; the overnight low will be just around 19 or 20°C.

Long Range

Temperatures will continue to be warm through the start of next week with partly cloudy skies and highs generally around the 30°C mark. Monday will likely be moderately humid again, but things will dry out on Tuesday as a cold front moves through. The rest of the week looks fairly quiet with near-seasonal temperatures and low humidity.