The heat will stick around for just one more day before a cold front ushers in cooler temperatures that will persist through the remainder of the week. That cold front will also bring the threat of severe thunderstorms to the Red River Valley this afternoon as it slides southeastwards through the region.
Today’s weather focus for Winnipeg & the Red River Valley will be the continued heat and humidity in place and the cold front that will be shunting it out today. Temperatures will rise quickly this morning towards a daytime high near 30-31°C. With dew points still in the 18-20°C range, humidex values will climb into the upper 30’s once again. By early afternoon, a cold front will start slumping southwards into the Red River Valley, bringing with it a risk for thunderstorms.
As shown in ECCC’s thunderstorm outlook, there is a chance for severe thunderstorms over the Red River Valley and southeastern Manitoba.
- Moisture: Surface dew points near 20°C will provide large amounts of energy for thunderstorms to work with.
- Instability: The high dew points will combine with moderately steep mid-level lapse rates to produce MLCAPE values near 2500 J/kg.
- Shear: Shear is lacking somewhat; 500 mb winds of 30-35 kt layered on top of south to southwesterly surface winds of 10 knots will produce bulk shear values near 25 kt.
- Trigger: A cold front slumping southwards through the region.
The high instability coupled with middling shear but sharp trigger will combine to produce the threat of severe thunderstorms that quickly develop into a multicellular line and move to the southeast.
The primary threat with today’s thunderstorm will be large hail. As shown in ECCC’s outlook, hail up to 5 cm diameter — a bit larger than a golf ball — is possible in the worst storms that form today. Heavy rain will be the second threat as it’s quite likely the rainfall coming out of the line of storms is torrential. Whether or not there’s overland flooding will depend on how quickly the line is moving; at this point, it seems like things will be progressive enough that while the rain will be heavy, it won’t reach severe criteria (50 mm in under 1 hour). There may be strong winds in some of the storms, but it won’t be as common as large hail and heavy rain. There is not a significant tornado threat today.
The biggest uncertainty will be when exactly the thunderstorms start. If they form early, around 1PM or so, then they’ll initiate to the northwest of Winnipeg and move through the city early to mid-afternoon. Should the capping inversion hold longer and storms don’t form until 3-4PM, then it will be likely that the cold front has passed through Winnipeg and the storms fire to the south and southeast of the city. The southern Red River Valley and southeastern Manitoba have a high probability of seeing thunderstorms this afternoon.
Behind the cold front, winds shift out of the northwest to around 20 km/h as skies clear. Temperatures will drop to a low near 17°C tonight.
Tuesday will start off sunny with skies becoming mixed in the afternoon as a weak disturbance moves towards the region. Temperatures will climb to a high near 26°C, but the humidity will be much more comfortable as dew points fall to the 11-13°C range in the continued light northwesterly winds. There may be a slight chance of some isolated showers in the afternoon. Tuesday night will bring some clearing in the evening, but then more organized cloud will begin moving in ahead of a low that will impact the region on Wednesday. Temperatures will drop to around 11°C.
Wednesday will bring cloudy skies and a good chance of showers to Winnipeg and the Red River Valley. It will be a relatively cool day with highs around the 20°C mark and continued light northerly winds. The chance for showers will taper off in the evening with temperatures dropping to a low near 11°C.
Long Range
The remainder of the work week looks quiet with temperatures near-seasonal, if not a bit below. There may be some chances for showers on Friday or Saturday, but it’s still looking a bit unclear at this point.
Winnipeg’s seasonal daytime high is currently 26°C while the seasonal overnight low is 13°C.
