Winnipeg managed to eke out a fairly pleasant Sunday with a cloudy morning giving way to sunny breaks in the afternoon as temperatures climbed up into the low 20’s. Showers that had the potential to impact the city ended up splitting as they entered the Red River Valley; one area headed to the north and across the Interlake while a second area of showers moved through North Dakota. Another chance for rain is on the way, though, with a low pressure system forecast to move through the region on Tuesday.

Attention now turns towards a developing low pressure system in Wyoming that will organize through the day today, strengthen tonight, and then move through the region on Tuesday.

Today will bring increasing cloud cover, particularly through the afternoon, but otherwise will be a pleasant day with a high near 22°C and relatively light winds. Tonight will bring mixed to cloudy skies with a low near 12°C as the low pressure system builds into North Dakota.

Tuesday’s forecast has a lot of room for error, but we’ll take a stab at broad generalities here. The short version: expect cloudy skies with a very good chance of seeing rain and/or thunderstorms beginning mid- to late-morning and tapering off in the late afternoon or early evening. Winds will pick up out of the north to northwest through the day to around 40 km/h as the low pressure centre moves through the Lake of the Woods region. Temperatures will top out near 15 or 16°C and drop to a low near 7°C on Wednesday night.

The long version: everything begins on Monday night as an area of thunderstorms develops across western North Dakota on the northern side of the surface low. These storms should expand in coverage through the night, spreading east-northeastwards along a warm front draped southwest-to-northeast across the state. This area of convective rainfall will spread into southwestern Manitoba late Monday night into Tuesday morning, then spread eastwards into the Red River Valley. At this point, there may be thunderstorms still embedded in the area of rainfall, but that risk will diminish through the morning. The rain will move eastwards through the day, then taper off in the late afternoon. With the convective nature of the rainfall, accumulations may end up being highly variable, but overall it seems like 10-20mm is quite likely, with higher amounts possible on a more localized level.

Now this is all fairly prone to error; primarily, a strong low-level jet is expected to develop across South Dakota along the eastern quadrant of the low, which may end up being a foci for thunderstorm development and rob this system of moisture that would have travelled further northwest or pull this system eastwards slightly faster, possibly causing the rain to pass to the southeast of the Red River Valley.

On Wednesday, the winds will remain gusty out of the north with temperatures climbing to a high, optimistically, near 11°C. Skies will start off fairly cloudy, but gradually break up a bit for the afternoon. Significant clearing will likely hold off until the overnight period as temperatures drop to a low near 2°C.

The remainder of the week looks dry with highs slightly below-seasonal and a fair amount of sunshine.

Winnipeg’s seasonal daytime high is currently 20°C while the seasonal overnight low is 5°C.