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.

Summer is Here!

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!



Summer is Pushing Into Southern Manitoba

The beautiful conditions we’ve had over the past while will take a slight break today, with notably summer-like weather pushing over the Red River Valley. With the Red River and Assiniboine River rapidly rising, how much rain will we see?

A low pressure system currently in Eastern Montana continues to push warm air northwards through the Dakotas towards Southern Manitoba. This warm air brought thunderstorms to Eastern Montana and the Dakotas overnight, and as they have pushed northwards, they have lifted up over the warm front and transitioned to elevated convection that, while weakened, is producing an area of rain that is pushing into our area.

As this precipitation continues to move northwards, away from the warm front, it will weaken as it looses it’s precipitation generating support. The rain that currently resides over the international border will slowly push north, and could give a few light showers to Winnipeg late this morning before it peters out. The main weather that will impact us is currently developing over southeastern Saskatchewan and Southwest Manitoba.

This area of rain visible on the southern edge of the RADAR image will continue to blossom as the low strengthens and overall lift in the area intensifies. This will then begin to track east-northeast later today and spread an area of rain across Southern Manitoba, including the RRV. The models are having some difficulties determining how much precipitation this will produce, which is to be expected, however their tracks for the precipitation are beginning to agree.




These models are all from their respectice 06Z runs, except the GEM-GLB which is the 00Z run, showing the precipitation accumulation from 00Z – 06Z tonight. The NAM is a big lighter on the precipitation, but other than that, they all agree (more or less) on location and intensity of the rain. So what will happen?

The precipitation accumulation will vary significantly depending on the amount of embedded convection that manages to develop. Current indications are that after a few showers late this morning, rain will begin to push across the Red River Valley late this afternoon or early this evening. The rain should end over the Southern RRV overnight as the low pulls further north and shifts the precipitation north as well. In Winnipeg, the rain should end sometime early tomororw morning; likely before 8 AM. Total rainfall amounts are difficult to pin down, as it will be directly proportional to the amount of convection that develops, but I would put my money on a general area of 5-10 mm (1/5 – 2/5”). If any significant convection should develop, some areas could potentially see up to 15mm of rain (~ 1/2”).

Once this precipitation clears out, the rest of the weekend will remain a little unsettled. The warm front maintains its position across ND, which will result in the chance of rain over the RRV as convection rides up over the warm front into Southern MB. Next week looks quite nice, however, with mostly sunny skies and temperatures in the low-to-mid teens. How all this precipitation will affect the river levels remains to be seen, however any accumulating precipitation has people concerned with the extremely high river levels that already are impacting the RRV. For more flood information, Rob over at Rob’s Blog has put together a nice collection of flood links.