Significant Rains for May Long Weekend

Balmy temperatures will be replaced by rain this long weekend as a significant low pressure system slowly pushes northwards into Southern Manitoba from the U.S. Northern Plains. Read on to find out just how much rain we can expect.

500mb Winds (12Z May 20th GEMREG valid 00Z May 23
500mm Heights & Winds from the 12Z May 20th GEMREG model run valid at 00Z May 23rd.

A powerful low pressure system continues to push northwards towards the Southern Pariries, slowly spreading rain through Southern Saskatchewan today and set to spread rain through Southern Manitoba tomorrow evening. This system is being fed by a frontal wave in the Central Plains, which is feeding moisture northwards into this low. This system is expected to continue to intensify over the next 24-36 hours, intensifying it’s rainfall production as it taps into increased instability and is fed additional heat and moisture from thunderstorms that develop and override the warm front in Nebraska and South Daktoa. Tonight, elevated thunderstorms will stream northwards through the Dakotas as they transform into larger areas of rain with embedded thunderstorms and wrap around the upper low, moving from east to west across Southern Manitoba and Saskatchewan.

This setup has the potential to produce significant amounts of rainfall. While models have been varying slightly in their position and amount of rain, they paint a fairly consistent picture:

24hr. QPF (12Z May 20 GEMREG valid 12Z May 22)
24 hour rainfall totals from the 12Z May 20th GEMREG model run valid at 12Z May 22nd.

24hr. QPF (12Z May 20 NAM valid 12Z May 22)
24 hour rainfall totals from the 12Z May 20th NAM model run valid at 12Z May 22nd.

24hr. QPF (12Z May 20 NAM valid 12Z May 22)
24 hour rainfall totals from the 12Z May 20th NAM model run valid at 12Z May 22nd.

As we can see, although the models all have varying amounts (highly dependent on how it resolves convection), they all paint a significant swath of precipitation heading our way. The GEM-REG keeps the precipitation the furthest south, and without a significant blocking ridge to the north, I’m inclined to think that it’s keeping things too far south. The current general agreement would be a swath of 0.75 to 1.5 inches of rain from Shaunovan/Swift Current through Brandon, Winnipeg and the Whiteshell.

For Southern Manitoba, we will likely see some showers or thunderstorms develop along the ND/MN border tomorrow morning and push northwards into Southern Manitoba by the early afternoon. This area of rain will slow as it approaches Winnipeg and begin to intensify into an area of rain. By late afternoon, it will likely be raining over most of Southern Manitoba and will last through most of the night. The Red River Valley will likely see a break late overnight into early Sunday morning before the rain starts again with wrap-around precipitation moving through. Winnipeg and the RRV will see approximately 20-30mm of rain if current guidance pans out, with strong east/north-easterly winds of 40km/h gusting to 60km/h.

Monday will see much cooler temperatures, with daytime highs for Winnipeg a mere 13° or 14°C under clearing skies. Next week looks cooler than this week, but we we should see plenty of sunny skies with temperatures quickly rebounding into the high teens/low twenties by the middle of the week.

Brad

Brad lives in Winnipeg with his wife and two children and is the founder of A Weather Moment. He has loved weather from a very young age and has followed that passion through his life so far. He received a B.Sc. in Earth Sciences with Specialization in Atmospheric Sciences and is currently employed in the field of meteorology. You can find the author as @WeatherInThePeg on Twitter.