Cool, Wet Weather For The Weekend

Winnipeggers: get ready for a shock. The next few days are going to be startling chilly with daytime highs over 10°C below normal and overnight lows over 5°C below normal. Another thing that will be noticably absent other than warmth? The sun will make only a few rare appearances over the next several days as another system pushes into Southern Manitoba, bringing another round of rain and thunderstorms to the Red River Valley.

850mb Temperatures valid 00Z Friday

850mb temperatures vaild at 00Z Sat. May 26 (Friday evening). An elongated cold trough is sweeping across Southern Manitoba, bringing 850mb temperatures in the -2 to -5°C range.

This cool weather has brought late-season (or is it early-season now?) snow to several communities over Western Manitoba including The Pas, Flin Flon and higher elevations over SW Manitoba (Duck Mountain & Riding Mountain areas). A few leftover flurries will scoot across the Interlake this morning and exit out of the province. The Red River Valley wil be spared, however we’ll be stuck under low clouds with a daytime high that struggles to make it to 10°C.

Tonight, a widespread frost potential exists over the most of Southern Manitoba. As a surface ridge moves into our area, winds will abate and we’ll see the cloud begin to break up a bit this evening. The greatest potential for frost looks to be over Southwestern Manitoba in the Virden, Melita, Pilot Mound & Brandon regions. Further east, here in the Red River Valley, some scattered clouds and a bit of moisture trapped in the valley should help temperatures stay above freezing, with overnight lows in the 2-3°C range. Areas outside the City of Winnipeg in the RRV certainly have a slight risk of a light frost. Winnipeg will likely be frost-free, with an off-chance of patchy frost in outlying areas near the Perimeter Highway.

Saturday will be our transition day with temperatures reaching 13-14°C and cloud streaming northwards from the Dakotas with the next incoming system. Rain will push up towards the International Border by morning, likely staying in the States but certainly poses the chance of a few showers along the border. The rain will stay near the border until Sunday, when the next big northward push arrives.

24. hour precipitation accumulation Saturday morning to Monday morning](

Precipitation accumulation from the GEM-GLB model for Saturday morning to Monday morning. A broad swath of rain is forecast to fall from extreme SW Saskatchewan through Southern Manitoba.

And what a push it will be! Showers and thunderstorms will rapidly develop into an expansive area of rain on Saturday night, slowly pushing northwards across the Red River Valley. Most regions across Southern Manitoba should expect rain to start fairly early on Sunday and last through most of the day. Rain will likely taper off from west to east overnight, with only a few wrap-around showers moving across the RRV on Monday. It’s still early to give accurate estimates of rainfall totals for this next system, however in general, most regions across Southern Mantioba look to see at least 10-20mm of rainfall, with the potential for nearly 30mm in some areas of the RRV if some embedded convection can get going. Regions of Southwestern Manitoba that end up north/northwest of the main upper low track will see higher amounts as well, with 20-30mm of rain likely. This isn’t the best news for this year’s Teddy Bears Picnic, but hopefully shouldn’t dampen spirits too much at an event that has, historically, had to deal with some pretty awful weather. Wait, I’m getting deja vu…

Conditions look to improve through the middle of next week, with temperatures pushing back towards the 20°C mark and some sun finally making an appearance. That’s a ways to go, though, so grab your slippers and heat up some soup! We have some great stay-inside weather coming up. We’ll be sure to keep a close eye on this system and provide updates in the comments.

Some Simple, Seasonal Weather

After a hectic few days across Southern Manitoba, Winnipeg is in for a few relatively calm, seasonal days before the next system moves into the region this weekend.

We’ll see the clouds breaking up this morning with a temperature that makes it up to around 19°C by this afternoon. We’ll see a slight chance of showers this afternoon, however they shouldn’t amount to very much and will quickly move out this evening. Tonight’s low will be around 10°C here in Winnipeg. Thursday and Friday will bring us a mix of sun and clouds with chances of afternoon showers across most of the Red River Valley as the upper low from yesterday’s system slowly tracks out of the Province. The daytime highs over the next couple days should be near 19°C.

A more significant system is forecast to move into our region this weekend, bringing what currently looks like a pretty rainy day to this year’s Teddy Bears Picnic.

Stormy Weather To Return to Southern Manitoba

After a cool night, temperatures will rebound nicely today before more unsettled weather pushes into the province tonight and lingers through mid-week.

850mb temperatures valid Tuesday Evening

850*mb* temperatures valid 00Z Wed May 23 (Tuesday Evening). Warm and cold front are represented by red and blue lines, respectively. Orange arrows represent warm air lifting northwards over the warm front.

Temperatures today will work their way to 20°C today with increasing cloud. The first of several impulses forecast to track across Southern Manitoba will push a warm front across the Red River Valley late this afternoon, bringing with it a good chance of showers
through regions along the Trans-Canada highway and northwards into the Interlake. Regions in the southern half of the Red River Valley will see just a chance of showers through the afternoon and evening today.

Tomorrow, a low pressure system will push into North Dakota, strengthening a warm front draped across the region. Southern Manitoba will stay north of the warm front, keeping daytime highs in the 20-23°C range. Strong capping will restrict surface-based thunderstorms to Central/Southern North Dakota where a cold front advancing across the Plains will help trigger storms later in the day. For us, however, we’ll be in great placement for the development of nocturnal convection. A strong 30-40kt low-level jet overriding the warm front will pump fairly moist air northwards; dewpoints at 850mb over Southern Manitoba are expected to rise to the mid-teens. Combined with negative lifted indicies, CAPE values are expected to climb to nearly 1500J/kg.

This will likely result in the development of showers and thunderstorms on Tuesday evening, developing somewhere over Southern Manitoba and pushing northeastwards through the night. Nocturnal convection is always a very tricky thing to forecast, so we’ll definitely keep a close eye on things and provide updates in the comments as we get closer.

The upper low associated with this system will push across the Prairies through the week, bringing a mix of sun and clouds and some unsettled weather and more chances of showers.

Showers and Thunderstorms on Tap for Southern Mantioba

While temperatures will soar to the 30°C mark today, much of the Red River Valley should be prepared for showers and thunderstorms to develop by mid-to-late afternoon as a low pressure system moves into the area and taps the available heat and moisture.

850mb Theta-E Values

850mb Theta-E values at 00Z May 19th (this evening) from the NAM. A sharp warm front is evident jsut north of the US border in Southern Manitoba.

With a strong capping inversion in place over the Red River Valley today, heat and moisture being pumped northwards will be trapped at the surface, allowing our temperature to soar to the 30°C mark and pooling moisture that will push our dewpoints up to around 15°C. Much of the day will be a beautiful day, especially given that it’s only May 18th. Conditions will deteriorate somewhat by late afternoon, though, as a surface low lifts northwards into Southern Manitoba.

The surface low will travel along a pre-existing surface trough and be supported by a shortwave ejecting northeastwards from the main upper trough, still anchored through Montana and Wyoming. With the heat trapped near the surface, the Lifted Index is expected to drop to the -2 to -8 values, with the lowest values running along a line from Gretna, MB to Bisset, MB and increasing to the southeast of that line. The heat combined with ample moisture is also expected to produce high CAPE values generally from 2000 to 3000J/kg. Increasing mid-level lapse rates with the approach of the shortwave will provide enough destabilization to erode the capping inversion through the afternoon and allow showers and thunderstorms to develop along and ahead of the warm front, initially concentrated near the triple point of the system. The showers and thunderstorms will expand in coverage as the evening progresses and the low-level jet intensifies.

Severe Weather Threat

Today marks one of the first severe weather threats of the season. Things look promising, and have even caught the attention of some seasoned storm chasers from the United States:

On paper, things look fairly good that there’s a risk for severe weather. EHI values rise to between 1.5-2.0 by late afternoon, which when combined with the presence of 30-35kt of bulk shear certainly presents the chance for supercell storms to develop. A few things hamper my excitement, though:

  • Bulk shear isn’t really all that impressive; the really good shear moves through Western Manitoba through the day today, lifting northwards into the Interlake. The shear diminishes to the SE and isn’t particularly strong where the greatest CAPE is. When it comes down to it, it’s likely that we’ll end up with marginally strong shear on top of marginally high CAPE this afternoon, with the most favorable conditions missing each other.
  • CAPE values may be too high. The NAM & GFS have been forecasting dewpoints slightly higher than have materialized. The amount of energy for storms to work with is going to be heavily dependant on the dewpoints that develop this afternoon, and if they don’t make it as high as forecast then we’ll be seeing weaker storms.
  • Too many storms. With so many marginally severe features, we may see quite a few showers and thunderstorms develop this afternoon as the cap erodes. If too many fire off, then it will be difficult for any one storm to oragnize itself into anything that poses a severe weather threat.

All that being said, a potential for severe weather does exist today across south-central and southeast Manitoba. The main threats should severe weather develop will be hail and/or the possibility of a tornado.

Thunderstorm Outlook for May 18th

Thunderstorm Outlook for May 18th to May 19th. Please note: Analysis has only been done for Manitoba. Storms may develop elsewhere in the Canadian Prairies.

Residents in Southern Manitoba should stay up-to-date on the weather today to ensure that if severe storms do develop, the appropriate precautions can be taken.