Week Comes To A Stormy End in Southern Manitoba

A complex low pressure system will bring several chances for thunderstorms to Winnipeg & the Red River Valley today and tonight into Saturday morning, some of which may be severe. All the unsettled weather will clear out on Saturday afternoon, leaving us with a seasonably mild and dry weekend.

The risk of thunderstorms returns to Winnipeg today as an approaching warm front moves into the region. As it advances eastwards, leftover cloud cover from overnight thunderstorms in Saskatchewan will spread into the Red River Valley. Before we get into the thunderstorm details, today’s high in Winnipeg will be a balmy 27°C with dew points climbing up to the 16-17°C range, making it feel a bit humid in the afternoon. Winds will be out of the south-southeast at about 20-30 km/h. Expect a low tonight near 18°C. Now, onto the thunderstorm details!

The first potential thunderstorm threat is for this afternoon, and will be focused primarily over southwestern Manitoba.

  • Moisture: Surface dewpoints will climb into the 15-17°C range ahead of the surface trough moving into the region. This moisture will be relatively deep, dropping only to around 13°C at 850mb.
  • Instability: MLCAPE values will climb to 1000-1500 J/kg of CAPE through the afternoon, although capping may be an issue depending on the timing of the 700mb thermal ridge passage.
  • Shear: Shear is fairly good with veering profiles and 45-50 kt of bulk shear. Low-level shear is relatively unidirectional with moderate speed shear.
  • Trigger: Low centre with trough line extending northwards will provide focus for low-level convergence. Additional, the triple point of a frontal wave tracking along the U.S./Canada border will also provide more focus and convergence.

The main uncertainties are tied to how quickly warmer air at 700mb1 can exit area. While it’s in place, it will likely prevent the development of thunderstorms until the evening. Should thunderstorms develop, the primary threats would be large hail and strong winds. The storms should be moving quickly enough that the threat for localized flooding due to rain is minimized, and higher cloud bases coupled with relatively small amounts of low-level wind shear will also reduce the tornado threat. If these thunderstorms develop, they will track eastwards into the Red River Valley in the early evening and make their way through.

The second thunderstorm threat will develop this evening and will impact much of southern Manitoba. Another disturbance will push into the region and initiate thunderstorms.

  • Moisture: The low-level jet will be supplying air with dew points near 16-17°C, providing ample moisture for thunderstorm development.
  • Instability: MUCAPE values will hover near 1000-1500 J/kg, enough energy to strong to severe thunderstorms.
  • Shear: Will be excellent; a very potent low-level jet will develop, strengthening to 50kt by 03Z. 500mb winds will be out of the west to southwest at 45-50 kt. This shear will be very supportive of thunderstorm development.
  • Trigger: Shortwave and associated frontal wave will be trigger for thunderstorm development.

Even now, there’s significant uncertainty with this afternoon’s convection. That said, it seems likely that thunderstorms will likely develop over portions of southwest Manitoba near 6-7PM and then undergo rapid upscale growth and develop into a line that tears eastwards across the Red River Valley; the primary threats associated with these storms will be large hail and damaging winds. Significantly elevated precipitable water values also suggest very intense downpours are likely as well.

AWM Thunderstorm Outlook valid 12PM Friday June 9 – 12PM Saturday June 10, 2017

Saturday will bring some more morning showers or thunderstorms, then breezy westerly winds of 30 gusting 50 km/h will usher in drier air in the afternoon as the clouds break up and clear out. Temperatures will climb up to a high near 23°C. Expect a low near 13°C under mainly clear skies on Saturday night.

Sunday will bring mainly sunny skies to Winnipeg with winds strengthening out of the southwest to around 30-40 km/h. Temperatures will climb to a high near 25°C. Winds will taper off Sunday evening as temperatures dip to a low near 15°C.

Long Range

Next week becomes quite uncertain as a major low pressure system develops in the Northern Plains of the United States and then slowly meanders northwards. As we move into summer, these systems will increasingly be driven by thunderstorms, which carry an inherent level of uncertainty, especially in the long range as how the various rounds of thunderstorm activity develop can impact the overall development of the low pressure system. That said, conditions will turn unsettled next week with near-seasonal to slightly above-seasonal temperatures.

Winnipeg’s seasonal daytime high is currently 23°C while the seasonal overnight low is 10°C.

An Additional Note

This will be the last forecast we issue here at A Weather Moment for the next while. We’ll be taking a bit of a vacation and won’t have our regular forecast posts on Monday June 12th or Wednesday June 14th. We suggest you check Environment Canada’s forecasts while we’re away!

  1. Approximately 3km above the ground.

Summer Heat Brings First Significant Thunderstorm Risk of the Year

The mercury will soar today thanks to the significant upper-level ridge over the region that has brought very warm air into the province. That hot weather will moderate a bit for the weekend, though, as a low pressure system moving through tonight will bring a threat of thunderstorms to the region and push temperatures down closer to seasonal values.

A scorcher is on the way today as temperatures climb above the 30°C mark across much of southern Manitoba. Southerly winds around 30 km/h will help bring up some humidity from the United States, and by the afternoon it may actually begin to feel muggy as well.

The weather will turn later this afternoon over the southwestern corner of the province as a cold front pushes eastwards across the province. Thunderstorms will develop near the Saskatchewan border mid- to late-afternoon and then grow into a line along the cold front as they progress eastwards through the evening.

Thunderstorms are possible across Southern Manitoba today with a risk of severe thunderstorms over the Parkland, southwestern portions of the province, and the western Red River Valley.

The biggest risk for severe weather will be in the afternoon during the early stages of thunderstorm development. Thunderstorms will have more energy to work with with temperatures in the 30’s combining with dew point values in the mid-teens providing 2000-2500 J/kg of CAPE. Shear will be a bit lacking, at 20-35 kt of 0-500mb bulk shear depending on the position with respect to the cold front.

That said, there’s a slight risk of severe thunderstorms across southwestern Manitoba tomorrow with the primary threat being large hail. Some of these thunderstorms may also produce strong to severe wind gusts.

The energy and dynamics to support these storms will shift as the evening progresses, with the best support slumping into the United States. As the line moves into the Red River Valley, the threat for severe weather diminishes, however thunderstorms will likely continue to roll eastwards through the night.

The expectation for thunderstorms to decrease in severity as they progress eastwards is based on the belief that models are being too aggressive in their advection of elevated dew point values into Southern Manitoba. If higher dew point values pushing into the upper teens do in fact show up in the region, the threat for severe thunderstorms will persist all night, and there would be an increased likelihood of a severe squall line along the cold front. Strong linear forcing could produce bowing segments with severe winds should that outcome occur.

The Weekend

Saturday will bring clearing skies in the morning, and then a few afternoon clouds with a slight chance of another shower or thundershower in the afternoon. The showers will move down from the northwest on the backside of Friday’s low, but as of writing it seems like most guidance suggests the showers will stay to the north and pass through the Interlake. That said, there’s a chance Winnipeg may see a little more rain in the afternoon.

The GFS is an outlier forecasting widespread showers across Southern Manitoba on Saturday afternoon

Aside from that, it will be a pleasant day with a high near 26°C and westerly winds to 20-30 km/h. Temperatures will dip to around 15°C on Saturday night with clearing skies.

Sunday will bring mainly sunny skies and a high temperature near 25°C to Winnipeg. Winds will be 15-25 km/h out of the north. All things considered, a great day!

Winnipeg’s seasonal daytime high is currently 22°C while the seasonal overnight low is 9°C.

Update: Mackenzie Low Brings Blizzard to Southern Manitoba

A potent Mackenzie Low dropped southeastwards through Saskatchewan yesterday riding along with a frontal wave that increased temperatures here in Winnipeg overnight. Behind this system is—for one of the first times this year—a potent Arctic air mass ready to surge southwards.

Today’s major weather features.

As a result, very strong winds developed in the rear of the cold front, supported through a deep layer as evident by a 120 km/h+ jet just off the surface that was visible on Doppler RADAR earlier this morning. Surface winds reached as high as 80-90 km/h behind the cold front which, combined with plenty of loose snow from our extra fluffy snowfall event the other day and some light falling snow, produced white-out conditions across many parts of Southern Manitoba.

The strong winds will move off to the east-southeast with the low pressure system through the morning and visibilities will improve. However, that bitterly cold Arctic air mass will move in through the day, sending temperatures south to around -26 or -27°C by the end of the afternoon here in Winnipeg. Temperatures will continue to drop to a low near -33°C on Friday morning with wind chill values of -42 to -45.

The cold weather will be short-lived as a mild Pacific air mass will begin building into the region this weekend.

Hang onto your Hat! Severe Wind Storm for Thanksgiving Monday

It will be a very windy Thanksgiving as a strong low pressure system ushers in potentially damaging winds. By the time you’re reading this your loose objects will probably already be in your neighbour’s yard!

Monday

Today will not be the most pleasant Thanksgiving, as rain and strong winds wreck havoc outdoors. A strong low pressure system and corresponding pressure gradient will generate high to extremely high winds over southern Manitoba on Monday. The highest winds are expected Monday morning, when sustained speeds of 60-80km/h, and gusts to 100km/h or more, are expected. The period of extreme gusts likely won’t last more than a few hours, but during that time it will certainly do some damage, not to mention the fact that you’ll have a lot more leaves to rake!

A strong pressure gradient (shown above as tightly packed black lines called isobars) will bring very windy conditions to southern Manitoba on Monday
A strong pressure gradient (shown above as tightly packed black lines called isobars) will bring very windy conditions to southern Manitoba on Monday

Today will also be rather soggy, as moderate rainfall occurs in association with this low pressure system. Today’s rainfall amounts will likely be around 5-15mm in the Red River Valley. You’ll have to wait until at least Tuesday for all those wet leaves to dry out!

Tuesday

Tuesday will be much calmer than Monday. Temperatures will climb into the mid teens under mainly sunny skies. Winds will remain breezy from the west, but they will feel light compared to Monday!

Wednesday

Wednesday will feature much the same weather as Tuesday. Temperatures will be in the low to mid teens under mainly sunny skies. Winds will be breezy from the north-west, but once again it will feel like nothing compared to Monday.

Long Range

Long range models continue to show a strong signal for warmer than normal weather through the end of October. Hopefully this will continue to be the trend as we move into winter due to the effects of El Nino.