Winnipeg will see very hot and unsettled conditions heading through the weekend.
A low pressure system crossing the province today will send temperatures soaring in Winnipeg. South-southwest winds of 30–40 km/h will usher in a hot air mass with highs climbing into the mid- to upper-30s. The dew point will stay in the low teens which will mean, fortunately, that the humidity won’t make the heat feel any worse than it already is. A “cold” front will sweep southwards through the Red River Valley later today. This front will bring a risk of thunderstorms to the region as it passes, although the most likely area to see any convection will be south near the U.S. border. Winds will shift to the north behind the front and then ease overnight. Temperatures will head to a low near 18 °C.
On Saturday, moderate southerly winds will bring more hot weather back into the region as another low pressure system moves into the province. Temperatures will climb back into the mid-30s but this time humidity will accompany it. Dew points will climb into the mid- to upper teens, making it feel closer to +40 out. That heat and humidity will meet another cold front pushing into the Red River Valley late in the day. This combination will bring a risk of thunderstorms — potentially severe — to the region Saturday evening and overnight. Temperatures will head to a low near 19 °C.
Drier, slightly cooler air will work into the region on Sunday. The morning will start with some lingering cloud with a chance of showers or thunderstorms as the cold front slowly continues to push through the valley. It should be off to the east by late in the morning with skies clearing for the afternoon. Temperatures will climb to a high near 27 °C with a moderate westerly wind bringing more comfortable humidity levels to the region. Skies will stay clear on Sunday night with a low near 14 °C.
Long Range Outlook
Next week will start with mainly sunny skies and highs near 30 °C again. Forecasts show more unsettled conditions developing mid-week, then gradual cooling back towards seasonal values by the weekend.
Today’s seasonal daytime high in Winnipeg is 22 °C while the seasonal overnight low is 9 °C.
Winnipeg will [likely] see record-breaking temperatures over the coming 3 days as a heat wave develops over the province.
Winnipeg will be scorching under the influence of a potent upper-level ridge this weekend. This potentially record-breaking warmth will pose a danger to those who have sensitivities to the heat, especially as overnight lows warm up in the low 20s. With little relief from the heat, it will be important to remain hydrated limit outdoor activities as much as possible late in the morning through the afternoon when the sun is at its highest.
So, how hot will it be? Today will be the initial day of significant heat in the region with temperatures increasing to a high near 35°C under sunny skies. Winds will increase to 15-20 km/h this afternoon. Temperatures will remain mild tonight with a low near 19°C.
Saturday will see even more heat build into the region as winds pick up out of the south to around 30 km/h. Temperatures will climb to a high near 36°C under sunny skies. Saturday night will see a very warm low near 23°C. Sunday appears to be even warmer than Saturday with southerly winds of 20 to 30 km/h continuing. Winnipeg should see a high near 37°C. A passing low pressure system on Sunday night will allow slightly cooler air to begin building back into the region. This should allow temperatures to dip to near the 20°C mark on Sunday night.
Fortunately, humidity levels will remain fairly average throughout this event. Strong evapotranspiration may lead to slightly humid conditions in the mornings, but as it quickly warms up the moisture should mix out of the boundary layer and return to more average values. Make no mistakes, though, it’s still going to be extremely hot.
Potential to Break Record Highs
This heat wave will spread significant heat that could potentially break records every day over the coming three days.
Record Temperatures in Winnipeg, MB for August 10-12
Record Maximum Temperature
Record Warm Minimum Temperature
Record maximum and record warm minimum temperature records for Winnipeg, MB valid as of August 9, 2018
Today will be a close one with daytime highs and overnight lows forecast near the existing records. Both Saturday and Sunday, however, show a strong likelihood of breaking both daytime maximum temperature records as well as record warm overnight lows. These records are derived from ECCC’s official observation database for Winnipeg and are inclusive from 1873-2017.
Long Range Outlook
As mentioned before, a low pressure system with a cold front will move through the region on Sunday night. It looks like the passage of the front will remain dry, but it should bring a return to near to slightly below-seasonal temperatures. Another warm-up into the upper 20s or low 30s is possible in the latter half of next week.
Winnipeg’s seasonal daytime high is currently 26°C while the seasonal overnight low is 12°C.
The heat wave across Southern Manitoba will continue through today and tomorrow as even more warmth and humidity build into the region. Significantly cooler air will move into the area on Sunday, behind a cold front passage on Saturday that will bring another round of potentially severe weather to the province.
Friday: Hot With Increasing Humidity
Today will be a hot day with increasing humidity as a deep southerly flow develops ahead of a deepening low pressure system ejecting northeastwards out of Montana. Temperatures will climb into the low 30’s with high temperatures reaching around 32 or 33°C this afternoon. Winds will also pick up out of the south to around 40km/h with gustiness on top of that. The humidity will be less than some days of late, but still fairly moderate with dew point values in the 18–20°C range. This will make it feel more like more like 37–40.
Some afternoon clouds will be about associated with the low pressure system lifting NE out of Montana. No precipitation is expected, though. We’ll have a very mild low temperature tonight of 21 or 22°C.
Cold Front Brings Severe Weather Threat for Saturday
Saturday’s weather story will be dominated by a cold front pushing eastwards across the Red River Valley. The southerly winds combined with pooling ahead of the cold front will make for very humid conditions with dew point values climbing to 23–24°C. With a high temperature near 33°C, it will feel more like the low 40’s and make for very uncomfortable conditions. As the cold front pushes eastwards, showers and/or thunderstorms are quite likely.
There are two possible outcomes for Saturday’s setup:
Nocturnal advection develops in the Northern Plains of the United States and pushes northeastwards. Scattered showers and thunderstorms persist over the Red River Valley through much of the day before clearing out with the cold front.
No or very little precipitation develops Friday night, leaving things dry and sunnier for Saturday. Severe thunderstorms would then be possible in the afternoon along the cold front.
At this point, it appears as if option 2 is the more plausible one. As always, looking at the MIST principles of thunderstorm development:
Moisture: Abundant. A deep layer of dew points ≥ 20°C will be in place over the Red River Valley, resulting in tremendous amounts of fuel for thunderstorms.
Instability: High. While the environment will be capped much of the day, significant instability will be in place through the mid- and upper-levels of the atmosphere. Steep mid-level lapse rates coupled with the high surface moisture will produce SBCAPE values in excess of 4000 J/kg and MLCAPE values of 3000–4000 J/kg.
Shear: More than enough. In general, a 40kt jet at 500mb over the region will combine with surface winds out of the south at 10–15kt to create around 25–35kt of 0–6km bulk shear. Hodographs show strong curvature, indicating likely supercell storm mode.
Trigger: The strong cold front pushing eastwards will provide focus for convection. While the capping inversion will hold surface-based convection back, the forcing from the frontal feature should be sufficient to initiate convection. 35–40kt southwesterly low-level jet may combine with steep mid-level lapse rates to produce elevated convection.
Given the extreme instability in place over the region (even elevated convection would have 1500+ J/kg of energy to work with), severe thunderstorms would be possible with either mode of convection. With the extremely high dew points in place, any thunderstorms that develop will be capable of torrential rainfall. Strong winds and large hail will be significant threats with any thunderstorms that develop. The threat of tornadoes cannot be ignored either; with strongly curved hodographs and such enormous amounts of energy, any supercell thunderstorms that develop would be capable of producing a tornado. The highest probability would be relatively close to the low pressure centre where the surface winds will be backed slightly more.
Saturday Severe Weather Update
Everything appears to be on track regarding today’s severe weather potential. There is a moderate risk of severe thunderstorms through much of the Red River Valley, Interlake and areas eastwards to the Ontario border. This includes large swaths of popular beaches & cottage country.
For the most part, all the expected conditions continue to pan out. Some elevated convection has developed overnight, however it doesn’t look like it will inhibit surface heating through the Red River Valley very much today. Very warm daytime highs in the low 30’s combined with dewpoint values in the 22-24°C range will combine to produce MLCAPE values of 2000-2500 J/kg and SBCAPE values exceeding 3000 J/kg. Combined with over 30 kt of 0-6km bulk shear and looping hodographs, there is sufficient energetics, dynamics and shear vectors to support strong supercell thunderstorms. Throughout the entire slight risk region, there will be a risk for large hail, strong winds and torrential downpours. Further north, in the moderate risk area, surface winds will be backed slightly more as the surface low pressure system continues moving northeastwards. Additionally, areas slightly further north will be closer to the upper-level jet and see enhanced 0-6km shear values. As such, any thunderstorms that develop in this region will pose a tornado threat, with the possibility of the production of a significant tornado today.
A strong cap in place will keep surface-based convection from triggering until late in the day as a trough pushes eastwards into the Red River Valley. Discrete supercell thunderstorms will likely develop between 4 and 6PM and then push east-northeastwards. As the line of thunderstorms pushes eastwards, upscale growth is likely as the system evolves into an MCS capable of all modes of severe weather.
Sunday will bring partly cloudy skies on the back-side of the low as it departs Manitoba. Significantly cooler weather will be in place with daytime highs of just 23°C expected. There may be a slight chance of some light, isolated showers, but the threat looks minimal at this point. Temperatures will dip to around 12°C on Sunday night.
Next Week? Quick Rebound
Taking a quick peek at next week, it appears that the cool down will be short-lived as significantly warmer air begins pushing back into the region mid-week. Alongside the warmer temperatures will come the potential for more unsettled, stormy weather.
A few showers may drift towards the Red River Valley from the NW this morning, however they should dissipate before it reaches our region. ↩
Temperatures will soar into the low 30’s over the coming days as a broad upper-level ridge continues to build across the Canadian Prairies, bringing with it some of the warmest temperatures of the year. Alongside the heat will come several bouts of humidity; at times over the coming days, humidex values – a “feels like” temperature that combines the effects of heat and humidity – will approach or exceed 40, making for exceptionally sweltering weather. In addition to the heat and humidity, today will bring a risk of severe thunderstorms…if they’re able to develop this afternoon.
Today will be a scorching hot day that will be made oppressively hot by the increasing humidity through the day. Temperatures will soar quite quickly today with the mercury reaching around 30°C by lunch time and then climbing a few more degrees above that this afternoon. All the while, the dew point will climb to the 19–20°C mark, resulting in humidex values in the 37–41 range for much of the day.
The biggest weather story for today, though, is the thunderstorm potential. First, here’s our outlook for today, but the discussion is important, so don’t skip over the rest!
A slight risk of severe thunderstorms exist across the Red River Valley, the Interlake region and eastwards to the Ontario border. Any storms that manage to develop today will have the potential to become very potent storms capable of all types of severe weather, including tornadoes, however there remains a single big question: will there be any storms?
As always, lets take a look at the basic MIST principles of thunderstorm forecasting:
Moisture: Ample moisture will be in place as surface dew point values climb to 20°C. 30mb mixed layer dew points are also expected to be in the high teens, which will make for ample fuel availability in convection.
Instability: Instability is strong but conditional. Given the high moisture values, MLCAPEs will sit in the 2000–2500 J/kg range while SBCAPE values may exceed 3000 J/kg. The crux is, however, the capping inversion. Strong insolation will chip away at the cap through the day, however 30–50 J/kg of inhibition will likely remain. The big question is, will the combination of surface trough and lake breeze interactions provide enough lift to break the cap? If any storms do manage to initiate, it’s all clear for explosive growth in a strongly unstable environment.
Shear: Shear looks fantastic for the development of strong, sustained supercell thunderstorms. 0–6km bulk shear values are expected to be in the 30–35 kt range while hodographs show excellent curvature. No questions exist about how favourable the shear is for supercell thunderstorm development.
Trigger: As mentioned above, two triggers will be in place today. The first is a trough line pushing through the Red River Valley & Interlake this afternoon. The second will be various surface boundaries developed through differential heating on escarpments (RRV, Gunton Bedrock) or lake breezes. It’s only slightly likely than any one of these features would be able to provide enough lift to trigger a thunderstorm, however if two or more of these features interact, it could trigger thunderstorm development. The trigger is the biggest uncertainty with today’s thunderstorm potential.
All these factors together combine to give a slight risk of severe thunderstorms across a wide region of Southern Manitoba. Despite the “lower” threat classification, all types of severe weather – flooding rains, large and damaging hail, severe wind gusts, tornadoes – are possible in thunderstorms in the Red River Valley today. The slight risk is given not for thunderstorm intensity – any thunderstorms that develop today could be very, very strong – but rather for the uncertainty associated with if they’ll even occur and expected isolated nature of the storms.
On tornado potential: Today brings with it a non-zero tornado threat, particularly for areas in the northern half of the Red River Valley and southern sections of the Interlake region. Hodograph curvatures are very impressive, and when storm-relative values are taken into account, helicities will be quite high in any thunderstorms that manage to develop. Cloud bases will be fairly high, but high dew points should help diminish significant evaporative cooling below the cloud base. Numerous parameters show favourable environments for thunderstorms capable of producing tornadoes as well. It’s impossible to forecast a tornado this far in advance, but if you live in the slight risk area, it would probably be wise to keep up to date on any watches/warnings issued by Environment Canada.
Temperatures will dip to around 19°C tonight with slightly less humid conditions.
Thursday: A Brief “Cool Down”
Marginally cooler air works into Southern Manitoba behind Wednesday’s trough line which will be reflected in daytime highs a whopping 1–3°C cooler, but still likely at 29–30°C or a touch warmer. Perhaps the bigger difference will be more tolerable humidity levels as dew point values drop into the low teens by the end of the day. Skies will be mainly sunny with relatively light northwesterlies as a ridge of high pressure builds in.
Winds shift southerly in the evening as the Red River Valley moves onto the back-side of the surface ridge and warmer air begins to push in again. Expect a low near 16°C.
Friday: Don’t Worry, It’s A Dry Heat
The heat is back on Friday with daytime highs climbing back to around 33–34°C. It won’t feel as hot as Wednesday, however, thanks to significantly lower dewpoints in the low- to mid-teens. While we’re not talking Arizona desert heat, it’ll be far more comfortable than the 20°C dew points earlier in the week.
Heading into Friday night, deep-layer moisture transport ramps up and will begin bringing significant amounts of moisture into the region aloft. This, combined with warmer air moving in, will lead to a fairly balmy night with lows near the 20°C mark.
Long Range: Severe Storm Threat Returns on Saturday
It looks like a threat of severe thunderstorms returns to Winnipeg & the Red River Valley on Saturday. Very humid conditions with highs in the upper 20’s will clash with a cold front moving in from the west. Showers and thunderstorms are probable with this front, and with significant energy and shear in the region, it’s entirely possible for severe thunderstorms to develop. It will all depend on the exact strength & timing of the cold front, so we’ll take a closer look at that on Friday when the event is closer.
Sunday will be a comparatively cold day with partly cloudy skies, a bit of a breeze and highs in the low 20’s.
Many studies show that some of the strongest supercell thunderstorms form in environments with between 25–50 J/kg of inhibition. ↩
At this point, we’re not expecting a huge line of thunderstorms to roll across the Red River Valley; rather it seems probable that there would be just one or two very strong storms. ↩
A Weather Moment is a non-profit website focused on weather commentary for the greater Winnipeg region as well as delivering useful tools designed to help acquire weather data for decision making processes. Usage of this website is subject to the terms of our disclaimer.