Tag: Thunderstorms

Mixed Bag of Weather Ahead

Brad Leave a comment

Winnipeg will see nothing but sunshine give way to unsettled conditions to start the week as a low pressure system moves into the region on Tuesday.

Thanks to a ridge of high pressure over the Red River Valley, today will be a beautiful day in Winnipeg. With nothing but sunshine and light winds, temperatures will climb to a seasonably cool high near 19°C. A low pressure system extending from central Saskatchewan into the Dakotas will being moving into the region tonight, bringing increasing cloud cover. Winds will remain light, though, gradually shifting from the north to the southeast. Temperatures will dip to a low near 9°C.

Tuesday will bring cloudier, unsettled conditions back to Winnipeg and the Red River Valley. The southeasterly winds will pick up to around 30 km/h, drawing in warmer air from the south and sending temperatures towards a high near 25°C. Winnipeg will see mixed skies and the chance for some shower or thunderstorm activity. The best chances for precipitation will occur near the beginning and the end of the day:

  • In the morning, but this will be highly dependent on overnight activity surviving as it moves eastwards. This looks unlikely for the Red River Valley, but north of Winnipeg may see some activity move across the southern Interlake.
  • In the mid- to late-afternoon as a trough of low pressure moves across southern Manitoba. This looks more likely.

The thunderstorms will have limited energy to work with, but strong shear will make an isolated severe thunderstorm possible. The chance for showers or thunderstorms will continue into the evening, tapering off at the latest somewhere between 10PM and midnight. Winds will be light overnight with temperatures dipping to a low near 14°C.

RDPS 12hr. QPF Forecast valid 09Z Wednesday June 6, 2018
Portions of the Red River Valley may see showers or thunderstorms on Tuesday evening

Wednesday will start off with some lingering cloudiness from Tuesday’s system. Northwesterly winds picking back up to 20-30 km/h will help clear it out for a mainly sunny afternoon. Once that sun does appear, it’ll allow temperatures to climb to a high near 21°C. Winnipeg will see clear skies and light winds on Wednesday night and a low near 11°C.

Long Range Outlook

The remainder of the week in Winnipeg looks increasingly summer-y. An upper ridge is forecast to develop over the eastern Prairies through the latter half of the week. This will bring warmer conditions back to the region alongside variable cloudiness. Some humidity may build back into the region this weekend too, with dew point values possibly reaching 17 or 18°C by Sunday. This would be just high enough to make it begin to feel muggy, but not be overwhelmingly humid.

Conditions will deteriorate to start next week as an upper trough replaces the upper ridge and the chance for showers or thunderstorms returns to the region.

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

Update: Severe Weather Threat Develops On Tuesday

Brad Leave a comment

There is growing confidence that the heat and humidity expected to move into southern Manitoba on Tuesday will bring severe weather to the region. Most areas in the south will need to keep their eyes to the sky and stay alert for any watches or warnings issued by ECCC, particularly for the afternoon into the evening.

Although conditions are fairly dry now, a strong low-level jet will advect significant amounts of Gulf moisture northwards into the region overnight. This will mix down fairly quickly in the morning, resulting in a rather startling transition from yesterday’s comfortable humidity to very muggy conditions. The heat and humidity will set the stage for some explosive thunderstorm potential on Tuesday afternoon.

ECCC is forecasting a severe weather threat for southern Manitoba on Tuesday

The focus for thunderstorm development will be a warm front that should lie close to the Trans-Canada Highway corridor by Tuesday afternoon. Storm development is a bit sensitive; in order for the storms to form, cloud cover from any overnight convection will have to clear out enough to allow temperatures to warm into the mid-twenties. Too much cloud cover or more nocturnal convection than expected? The warm front could shift south, daytime heating could be limited, or — if the nocturnal convection was vigorous enough — much of the existing mid-level instability could be consumed.

That said, guidance suggests that much of the Red River Valley and areas east should see enough sunshine to warm things up so we’re going to go ahead and assume that’s correct.

Starting with the foundations and looking at the MIST principles:

  • Moisture: Significant moisture with deep-layer dew point values climbing to nearly 20°C. A well-organized southeasterly flow within the warm sector will sustain and replenish low-level moisture through the day.
  • Instability: 850-500 mb lapse rates between 7 and 8°C will combine with the high dew points and temperatures in the 26-28°C range to produce 1500-2000 J/kg of MLCAPE. Lifted index values near -9 reflect the significant instability associated with this system. Capping should not be too much of an issue with a 30-40 J inversion forecast to erode in the afternoon.
  • Shear: Perhaps the weakest looking aspect of the day; while the column shows favourable veering with slightly looping low-level hodographs, inflow winds will be weak. Some decent winds in the low- and upper-levels, but mid-level winds are also lacking a bit. All in all, probably enough shear to organize things, but linear shear looks stronger than the twisting, so thunderstorms will likely line out fairly quickly.
  • Trigger: A prominent warm front draped across the region will provide the focus for convective initiation.

The next 24 hours looks to generally play out something like this for the Red River Valley: first, a few elevated non-severe thunderstorms will develop tonight ahead of the warm front as it lifts northwards and move through the region early Tuesday morning. They’ll clear out by mid-morning, leaving behind mixed skies. The heat and humidity will quickly build, and new thunderstorms will develop along the warm front mid-afternoon. These thunderstorms will initially develop as discrete supercells or multicellular clusters, then grow upscale into some sort of QLCS1. The primary threats from these thunderstorms will be large hail and damaging winds. Of particular concern will be the potential for a bow echo to form on the northern edge of the warm front and track eastwards along the frontal boundary, producing an extended swath of strong to severe winds.

This simulated RADAR forecast for Tuesday evening shows what we expect: active across southern Manitoba with the potential for severe thunderstorms

While the possibility of a tornado cannot be completely ruled out, the relatively weak inflow winds limit it to an unlikely and isolated threat.

The thunderstorms will push northeast of the Winnipeg and the Red River Valley in the evening. The severe weather threat will likely be over by 9 or 10 PM.

Although I haven’t gone into it too much, it’s worth noting that this severe thunderstorm threat continues westwards into southwestern Manitoba. In addition to the severe weather threat, the region also faces greater risk of significant rainfall as moisture lifted up into the atmosphere by the thunderstorms runs into this system’s deformation zone, likely creating a slow-moving southwest-northeast band of showers and/or thunderstorms through the Parkland and Interlake capable of producing substantial mounts of rainfall.

This is, of course, just the best forecast we can provide at the current time. A lot of this hinges on thunderstorms developing overnight in the expected way and that can be a precarious thing to depend on. That said, it’s definitely worth keeping an eye on things tomorrow and keeping aware of any watches or warnings issued by Environment Canada.

  1. QLCS stand for quasi-linear convective system and denotes the general family of thunderstorms that develop along lines such as squall lines and bow echoes. ↩

Unsettled Weather Returns To Winnipeg On Tuesday

Brad Leave a comment

Winnipeg will see another beautiful, warm start to the week, but another low pressure system pushing northwards out of the United States will bring showers and thunderstorms back to the region for Tuesday and Wednesday.

Under the influence of a broad area of high pressure, Winnipeg will see beautiful conditions today with plenty of sunshine and a high temperature near 28°C. Winds will be light and humidity will be comfortable, leaving little to complain about! Later in the afternoon, a bit of cloud will begin spreading into the Red River Valley as a low pressure system begins moving into North Dakota.

Temperatures will remain mild tonight as warmer, humid air begins building into the province as the North Dakota low continues to approach. Temperatures in Winnipeg will drop to around 17°C with winds picking up out of the south to around 30 km/h. A few showers or thunderstorms may develop and move through the region overnight.

Winnipeg will see humidity levels increase on Tuesday as dew points climb into the upper teens; combined with a high near 29°C, humidex values are forecast to reach into the mid-thirties. The morning will bring mixed to cloudy skies as any nocturnal convection finishes moving through, then Winnipeg and the Red River Valley will see a few sunny breaks through the early afternoon.

RDPS 2m Dew Point Forecast valid 18Z Tuesday May 29, 2018
Humid conditions will return to Winnipeg and the Red River Valley on Tuesday

As the heat and humidity builds, showers and thunderstorms will likely develop across much of southern Manitoba in the afternoon. Triggered by the incoming disturbance from North Dakota, the showers and thunderstorms will spread northeastwards through the night. There is a small chance some of these thunderstorms could be severe with large hail being the primary threat. There are indications that a few areas may see some training thunderstorms with local rainfall accumulations of 25-50 mm.

Wednesday will be a much cooler day in Winnipeg with high temperatures only near 22°C. While this is significantly cooler than the city has seen over the past while, it’s in fact near-seasonal for this time of year. Skies will remain mostly cloudy with a good chance of showers as the low centre itself moves through the region. Some breezy northwesterly winds will move in through the afternoon, picking up to around 30 km/h.

Skies will remain mostly cloudy on Wednesday evening with northwest winds near 20 km/h and a low near 14°C.

Long Range Outlook

Winnipeg will see a break from the heat through the remainder of the week with near-seasonal temperatures forecast. Skies look cloudier than not, with generally unsettled weather returning for the end of the week into the weekend.

Winnipeg’s seasonal daytime high is currently 22°C while the seasonal overnight low is 8°C.

Slight Risk of Thunderstorms Ushers In A Pleasant Weekend

Brad Leave a comment

Winnipeg will see a slight chance of a thunderstorm this afternoon, then see conditions settle for a pleasant weekend.

It will be another hot day in Winnipeg today as temperatures climb to a high near 30°C. Today’s humidity will be lower, making the heat more comfortable than the muggier conditions that were in place yesterday. Scattered showers and thunderstorms will develop over western Manitoba this afternoon and move southeastwards. Winnipeg will be on the eastern extent of this activity and will see a slight chance of a thunderstorm late in the afternoon or early evening. Skies will remain partly cloudy overnight as temperatures dip to a low near 15°C.

RDPS 2m Temperature Forecast valid 21Z Friday May 25, 2018
Daytime highs will once again climb to near 30°C over the Red River Valley today

Saturday will be a lovely day with mixed skies and a high near 25°C. Winds will be a bit more noticeable out of the northwest at around 20 km/h. Skies will clear out for the evening with temperatures dipping to a low near 15°C on Saturday night.

The heat returns to Winnipeg on Sunday, sending temperatures to a high near 28°C. Cloud cover will increase over the Red River Valley for the afternoon, making for a comfortable afternoon: warm but with a break from the sun. Temperatures will head to a low near 14°C on Sunday night under mixed skies.

Long Range Outlook

Monday looks to be much like Monday, then the humidity returns for Tuesday with unsettled conditions bringing the chance of showers and thunderstorms back to the region.

The rest of the week will bring variable cloudiness and seasonably warm temperatures.

Winnipeg’s seasonal daytime high is currently 22°C while the seasonal overnight low is 8°C.

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