A low pressure will eject east across the Northern Plains on Wednesday. This will drag along a cold front and a large warm sector. Southern Manitoba will be in the warm sector on Wednesday afternoon, which will allow warm temperatures and moisture to invade parts of the province.
Temperatures could reach the 30C mark on Wednesday late afternoon for parts of extreme southeastern Saskatchewan and extreme southwestern Manitoba.
With the warm summer-like temperatures expected and the moisture advecting northward, severe thunderstorms are likely. With moisture in the mid-50s (F) will provide ample fuel for storm development. As seen below, moisture will be well into central Manitoba. It will be a warm and muggy day tomorrow for Manitoba/North Dakota.
While moisture provides the fuel needed for storms, fairly modest instability values are also expected across North Dakota and Manitoba. Mixed-layer CAPE values should be in the 1000J/kg value, which is pretty high for this time of year. This will provide ample instability for storms to become severe with large hail/damaging winds.
While severe storms are likely in North Dakota, severe storms are more conditional for Manitoba. Morning rain showers will swing through and redevelopment of strong/severe storms will depend on how much airmass recovery can occur in Manitoba. If strong heating can occur, areas such as Killarney to Morris could see severe storms tomorrow. Regardless whether storms reach severe levels or not, gusty winds and heavy downpours are likely for areas from and east of Killarney-Carman-Morris line.
...Northern Plains... As a shortwave trough crests a midlevel ridge, a surface low will develop and move across the Canadian Prairies. A trailing surface trough will move across the Northern Plains during the afternoon/evening. Strong heating/mixing near and west of the surface trough and at least modest large-scale ascent attendant to the midlevel shortwave will support isolated thunderstorm development across central/eastern ND by late afternoon. While boundary-layer moisture will remain relatively limited, dewpoints in the 50s F, temperatures warming to near 80F, and steep midlevel lapse rates will support moderate instability along and ahead of the surface trough. Effective shear/helicity will be sufficient to support organized structures, with potential for isolated supercells capable of large hail and locally severe wind gusts. Some upscale growth is possible into Wednesday evening into portions of western/central MN. However, increasing MLCINH and decreasing buoyancy with eastern extent should result in a gradually diminishing severe risk through the night.