As Manitobans in the Southwest corner of the province continue their battle against the swollen Assiniboine river, mother nature has granted us tremendous weather. Clear skies and warm temperatures have spread throughout much of the province, giving us a reprieve from the cool and cloudy conditions that we seemed to be entrenched in for…well a long time. But will it last?
An “omega block” set up across the Prairies late last week, with the jet stream rounding the base of an upper low off the coast of California and then heading up to the Northern Prairies, arching over an upper high that had built into the central Prairies and then heading south and exiting the continent around the bottom of an upper low off the east coast. This allowed a large-scale southerly flow to develop and warmer air to push northwards into Canada. As a side note, this is called an “omega block” because the jet stream curves in the shape of the Greek character omega, and it’s a fairly stable pattern that doesn’t move very quickly, hence it’s a blocking pattern.
Over the past few days, a shortwave has pushed into Alberta and the blocking pattern has begun to shift. Instead of completely collapsing, it seems to have rotated such that the block is now aligned northwest-southeast instead of north-south. This will allow cooler air to push into the western Prairies (as is seen today with cooler temps and rain through southwest Saskatchewan) while building the warm air over the eastern Prairies.
Stormier weather is brewing to our south, though. A significant shortwave is expected to eject northeast out of a stationary long-wave trough on the upper-west coast on Thursday night, moving into the Dakotas by Saturday. This feature has a lot of uncertainty attached to it at the moment, but the models have been pushing the precipitation envelope further north with each successive run, which puts Winnipeg increasingly into the risk of some rain ruining our lovely weather.
12 Hour QPF valid 06Z Sun 22 May from the GFS Model
I’ll provide some further details about this system in a couple days when it’s beginning to resolve a bit better. It looks likely that areas south of Morris in the Red River Valley will likely see some accumulating rain this weekend, but first we get to enjoy several more days of hot, sunny weather. Get out there and enjoy it!