A series of weak disturbances will bring more cloudy days for Winnipeg with a chance of showers across the entire Red River Valley overnight and through the weekend.
GEM-Global 12hr. QPF valid 00Z May 5 to 12Z May 5 (Friday night). Notice the relatively small amounts over Manitoba compared to the 2”+ rainfall accumulations near the North Dakota/South Dakota border.
A shortwave tracking northeastwards is pushing into Southern Saskatchewan this morning, supporting a band of rain in the associated trough over SW Manitoba. As this system pushes northeast, the upper-level support will weaken and the band of rain will begin to diminish and become more “shower-y”. As the weak upper trough passes through the Red River Valley overnight, an area of nocturnal convection will develop in southern North Dakota, centered around some slightly enhanced lift from a weak low pressure system.. Models want to initiate a band of showers all the way along the upper trough that will be positioned between the ND low and the SK shortwave; however, any showers that want to try and develop may have to contend against subsidence north of the nocturnal convection in ND. Should this happen, either the SK shortwave would need to track further south than currently forecast to provide enough lift to offset the increased subsidence from the storms or the storms would need to fire further south so that more instability remains over the RRV. Otherwise, we’ll likely see little to no precipitation in the Red River Valley tonight. Were I to produce a standard EC forecast, I’d say that the north half of the RRV has a 40% chance of showers tonight and the southern half of the RRV has a 60% chance of showers.
Another system is forecast to track through on Saturday night into Sunday, bringing with it another chance of showers for Southern Manitoba. Once again it’s a binary system: the band of precipitation will be supported by two shortwaves, one in Canada and one in the US. As the system moves into the Red River Valley, the northern shortwave pulls northwards and the southern shortwave slides SE a bit, resulting in a good chance that the main band of rain will split apart and miss much of the RRV with the northern half pulling into the Interlake and the southern half sliding into North Dakota.
Again, with these convective systems, forecasting is a challenge. Over the next few days, expect more cloud than sun, daytime highs between 10 and 15°C, and a chance of showers tonight, Saturday night and Sunday. We’ll be providing updated forecasts when possible in the comments below, so be sure to check them over the next couple days.
