Environment Canada has issued a severe thunderstorm watch for most of southern Manitoba for this evening. A few thoughts on the coming hours…
For Southwestern MB:
The main threat for severe storms should end this evening. High temperatures and dewpoints combined with daytime heating have contributed to a favourable environment for severe thunderstorms. These ones should primarily be driven by the sun, so once the sun starts going down, so too should the intensity of the storms.
For the Red River Valley:
The main threat for severe storms will continue through the evening as an 850mb jet pushes up out of North Dakota into the RRV. The main threat with these storms will primarily be rain. The storms are developing on the nose of the 850mb jet, just downwind of an area of moisture convergence, so as the evening continues, the storms will have more and more moisture to work with. This, combined with the fact that storms will most likely be training (multiple storms moving in rapid succession over the same area), will result in some areas in the RRV getting large quantities of rain. My initial estimate would be that some areas will receive total amounts of 70-90mm locally, however it could potentially be higher than that. Most areas will probably receive on average 15-25mm of rain.
Other threats from these storms will primarily exist during the evening hours when they still could be surface based. If any storms can develop by themselves this evening, there’s a slight chance they could become supercells given the SSE flow through much of the RRV. If that is able to happen, then there would be a chance of large hail (my estimates would be quarter to loonie sized) and strong winds (90+ km/h). Give the backed surface flow, there would also be a very slight chance of a supercell becoming tornadic, but the overall setup doesn’t look to favourable for that; you never know what storms will do when working with 3000+ joules of CAPE, though.
This MCS will stick around for a good portion of the night, resulting in a widespread wet and noisy evening for many residents in Southern Manitoba.