Updated: Jun 21, 2019
An ongoing severe weather threat in Alberta will move east over the next few days. Some fairly complex maps are to follow, but for you in Manitoba, Thursday late evening, you could see a strong storm or two near the SK/MB border and Friday is really the "bigger" day for strong thunderstorms in southern Manitoba.
Below is a depiction of possible storms in southern Saskatchewan on Wednesday/Thursday:
Wednesday the Low impacting Alberta will begin to "occlude". This front will act as a cold front and slice through an unstable airmass in southern Saskatchewan Wednesday afternoon. This will trigger a line of storms from Unity, SK to eastern Montana lasting well into the evening. Storms will lose strength as daylight fades. This line of storms may continue through the night and bleed into our discussion from Thursday (below).
Threat level: MEDIUM
Thursday will feature a marginal risk of storms in Saskatchewan/Manitoba depending on whether storms can redevelop or not. An ejecting Low from Wednesday will bring a large precipitation area ahead of the front most of the day in parts of central SK/MB. This will substantially limit the amount of destabilization south of this precipitation "shield". The amount of instability will be quite sparse. If storms are able to develop, it will likely be late in the day near the MB/SK border, where they should move northeast from there.
Thursday Morning Update:
Airmass recovery will be very difficult to near impossible in SK/MB due to substantial cloud shield currently ongoing with associated precipitation. No severe storms are expected to redevelop later today.
Threat level: NO SVR WEATHER EXPECTED
Friday will be the day to watch. A pretty "textbook" warm front/cold front scenario will happen for southern Manitoba. The warm front will lift north throughout the day, bringing warm southerly winds into southern Manitoba. As the cold front slices through North Dakota, severe thunderstorms will erupt.
Many uncertainties remain for storm development in southern Manitoba on Friday. Things such as cloud cover and/or early storm initiation may put a damper on the severe threat, however looking at past similar setups and the deepening Low pressure, we think a medium to high threat could be in order. Some supercells will be possible in southern Manitoba (possibly coming from North Dakota), with large hail and damaging winds being the main risks at this point, however there is a tornado threat there for sure.
Thursday Morning Update:
Airmass recovery will be difficult in the warm sector (southern Manitoba). Storms will be ongoing early in the period, which will limit instability for S Manitoba. Given kinematics in place, 1 or 2 embedded supercell structures may be possible closer to the Low Pressure. Somewhere along the SK/MB/ND borders. Reduced threat to MEDIUM.
Friday Morning Update:
Forecast remains on track. Instability remains the biggest concern with today's severe potential. Somewhere along the SK/MB/ND could see a strong storm or too, with main threats being heavy rain, localized flash flooding and strong wind gust or two. Some models are still showing a line of strong storms developing near the MB/ND border and moving into Manitoba, if this occurs, damaging winds and very heavy downpours could accompany them. Some possible embedded multicell structures could accompany them. Kept the medium threat level to accounted for organized storms. Regardless, heavy downpours will occur today.
Threat level: LOW to MEDIUM