Threat level: HIGH
Confidence: HIGH (based on model agreements)
Expected hazards: VERY LARGE HAIL (up to baseballs) // DAMAGING WINDS // TORNADOES // FLASH FLOODING
Locations impacted: Russell, Shoal Lake, Brandon, Souris, Melita, Killarney, Virden, MacGregor, Neepawa, Pipestone, Peguis, Asher, Dauphin, Sandy Bay and surrounding towns (in Manitoba)
Timing: 4:00 pm CDT to 8:00 pm CDT
Discussion: steep lapse-rates, little to no convective inhibition ahead of the front, very high mixed-layer instability and ample moisture will make for a volatile setup for severe weather in southern Manitoba on Wednesday. What makes this setup that more "dangerous" is that one or a few lone supercell(s) is/are expected to form (somewhere in Westman) and track south-southeast into southwestern Manitoba. These lone supercells will have all hazards possible (including some tornadoes or possibly one stronger tornado), possibly for several hours, as it taps into unlimited instability/moisture with little competition. Storm mode is expected to be high-precipitation (HP). With this type of storm mode, heavy rain leading to flash flooding and very large hail can be expected. The tornado threat could be dampened by the evaporative cooling common in HP cells, which tend to easily undercut the updraft. Early initiation or overnight storms could also limit strength of storms. However, local terrain enhancements and possible outflow boundaries could compensate and enhance low-level shear. While we think the NAM 12km is overdoing instability, we still think that 2000-3000J/kg of MLCAPE could be realized in southern Manitoba on this day and for this reason have issued a HIGH risk of severe weather for this day.
While we expect severe weather on Thursday as well in Manitoba, you will need to stay tuned for an update as we would like to see how the models handle tomorrow before we feel confident enough for a forecast.
Here is the outlook for tomorrow in Saskatchewan/Alberta/Manitoba issued by the PASPC:
Area(s): Easternmost parts of southern Saskatchewan
Timing: Wednesday afternoon into the early evening
Threats: 2-4 cm hail, gusts to 100 km/h
Remnants of any severe thunderstorms should have moved into southwestern Manitoba by noon, however a low pressure trough with very warm humid air associated will trigger new thunderstorms in areas south of Hudson Bay and near the Manitoba border. Some of these thunderstorms may become severe with 2-4 cm hail and wind gusts up to 100 km/h. Non-severe thunderstorms will likely also occur from Kindersley southward through the Cypress Hills then eastward near the US border in the afternoon along a weak cold front, with more occurring in the afternoon in areas east of Prince Albert. More non-severe thunderstorms from Alberta will drift into the northwestern grainbelt overnight.
Area(s): Southern Manitoba
Timing: Wednesday afternoon and through much of the night
Threats: 3-5 cm hail, gusts to 110 km/h, plus a tornado threat
Ongoing thunderstorms from Saskatchewan will likely drift into the Parklands area during the morning hours - these will be strong to marginally severe. As they move off into the Interlake and weaken, new thunderstorms will form in the Parklands area in the late afternoon, with an initial tornado threat until mid evening after which time the storms will likely form into a squall line with more of a wind and hail threat which will march towards the Red River Valley by late evening and early overnight. Most of the storms should weaken towards morning as they move into Northwestern Ontario and Minnesota