Miserable weather during the May Long Weekend has been a long tradition in Manitoba. This year is going to take the cake. Weather warnings have been issued across southern Manitoba in anticipation of significant amounts of rain, very strong winds and even some snow and ice pellets.
The worst of the weather will be tomorrow and Monday so enjoy today while it lasts! It will actually be quite mild today with highs in the low 20's along with light winds. Clouds will thicken ahead of our upcoming storm. An odd shower or two may occur this afternoon but the big rain event doesn't begin until this evening. Rain may be heavy at times through the evening and overnight. Some thunder will be possible, but I don't expect a significant amount of it for Winnipeg. The bulk of the thunderstorm activity will be confined along and south of the US border.
Showers may taper off a bit in the morning tomorrow, but a second wave of heavy rains will move in later in the morning and in the afternoon. A strong cold front coming down from the arctic will meet up with the Colorado Low tomorrow as well, ushering in much colder air and very strong north-northeast winds. Temperatures will plummet tomorrow afternoon and reach close to the freezing mark by late evening. This may cause precipitation to switch over to ice pellets or snow in the evening. Winds will be very strong tomorrow as mentioned already. They may be sustained between 50 and 65 km/h with gusts of 70-90 km/h.
Light snow or ice pellets will continue through to Monday morning. Some clearing may occur in the afternoon or evening. Strong north winds of 40 gusting to 50-60 km/h will continue, tapering off late in the day.
In total, 30-60 mm of rain could fall this weekend throughout the Red River Valley including Winnipeg. Locally higher amounts can't be ruled out, especially under thunderstorms. In terms of snowfall, a few slushy cm are possible for the Winnipeg area specifically. Higher snowfall amounts are expected in southwestern Manitoba.
Note that Winnipeg has not seen snow this late in the season since 2002 when a trace cm fell May 23. In addition, snow has fallen on May 18 only 4 times since 1872. The most we have seen on May 18 is 3.0 cm in 1963. A record low maximum is also possible Monday with the old record being 4.4°C in 1968.