Tornado Threat To Develop Over Southern Manitoba on Saturday

3km EHI Values

3km EHI Values. This measures the potential strength of a tornado should one develop. As can be seen, the GFS EHI values have gone off the chart over extreme SW Manitoba on Saturday afternoon.

A slow-moving low pressure system pushing into our region will set the stage this weekend for the potential of supercell thunderstorms capable of producing localized flooding, extremely large hail, damaging wind gusts and tornadoes. Read past the break to get all the details, our thoughts on the main threat areas, and to see updated information in the comments.

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An extremely slow-moving long-wave trough has been slowly pushing it’s way eastwards this week. While it’s been a good distance from us, we’ve been able to enjoy the benefits of such a setup: plenty of nice, warm weather with comfortable humidity. Our friends in the Western Prairies haven’t had it quite as nicely; multiple rounds of storms have pushed into Southern Alberta & Southwestern Saskatchewan over the past couple days, bringing multiple tornadoes to Southern AB and torrential rain that caused localized flooding after 2-3” fell in a short period of time. Large hail was also reported in many storms across the Western Prairies, as well as with some severe thunderstorms that developed over SE Saskatchewan on Wednesday evening.

Entrance of this system in our region has been marked by the thunderstorms and showers that developed overnight. We should see most of these clear from the Red River Valley this morning or by early afternoon if they’re really tenacious. We’ll see a relatively pleasant afternoon, with some lingering cloud and temperatures in the low-to-mid 20’s. The dewpoint will be quite high, making it feel a little sticky, though.

The main surface low begins to move into our area on Saturday, pushing a warm front up from North Dakota into extreme Southern Manitoba. Using the basic MIST principles of thunderstorm forecasting:

  • Moisture: Plentiful. Surface dewpoints will be sitting near 20°C across Southern Manitoba, with 850mb dewpoints pushing up towards 15-17°C. This deep layer of moisture will provide plenty of energy for storms to work with.
  • Instability: The major inhibition to storms will be a layer of warm air at 700mb. Temperatures will climb to 10-13°C at 700mb on Saturday morning, however cooler air will push in later in the afternoon, helping destabilize the mid-levels. LI values of -8 to -11, combined with CAPE values anywhere from 2500 J/kg to 5500 J/kg are evidence of an extremely unstable atmosphere.
  • Shear: With a decent upper-level jet pushing in through the day, most areas across southwest and south-central Manitoba will see bulk shear values increase to 30-40kt by evening.
  • Trigger: A warm front draped across Southern Manitoba will be strong enough to initiate convection in the mid-to-late afternoon as the cap begins to erode.

Prog Tephi for SW MB

Prognosis tephigram for Southwestern Manitoba on Saturday afternoon. Note the extremely favorable veering wind profile present.

Models strongly disagree about the speed of this system, but agree that it has a very strong potential to produce damaging supercell thunderstorms capable of producing tornadoes. The greatest uncertainty, then, is where exactly the storms may form. Unfortunately, as I write this it’s still too early to tell exactly where the greatest threat lies. The slowest solutions would place the main risk over extreme SE Saskatchewan across SW Manitoba, while the quicker solutions would place the risk over SW Manitoba into the Red River Valley. Personally, I feel that the slower solutions are probably a little more true to what’s going to happen. With that in mind, here’s my threat area for Saturday:

Day 2 Storm Outlook

Day 2 Thunderstorm Outlook, valid Saturday afternoon through Sunday morning. This is subject to refinement as this system develops and more certainty exists on it’s track and speed.

A large MCS will likely develop as the whole system lifts northwards overnight, which will continue to provide a severe weather threat in the form of strong winds and large hail. It will push through the RRV by Sunday morning. We may see the threat for another round of thunderstorms on Sunday afternoon, however they are not expected to be severe. Things will finally cool off on Monday as the main upper low moves through and draws in cooler, dryer air from the west.

We’ll be sure to refine the forecast in the comments below as the day approaches. In addition, it looks like the AWM crew will be out chasing, so we’ll be sure to have some live updates should everything work out. Stay sky aware out there this weekend!

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A Scorching Week to End With A Bang

Temperatures are set to soar for the remainder of this week as heat sourced from the Gulf of Mexico builds into Southern Manitoba. Residents across all of Southern Manitoba should begin to prepare for a potentially dangerous end-of-week though, as a powerful low pressure system will threaten the first significant severe weather outbreak of the season.

850mb Theta-E Chart for 06Z Thursday

850mb theta-e (a form of measuring temperature) chart valid for 06Z Thursday 07 May. The light-red arrows depict the advection of heat from the Gulf of Mexico through Southern Manitoba.

A southerly flow of air aloft, aided by a long-wave trough over the Rocky Mountains to our west and a blocking high to our east, will bring us our hottest days of the year through the rest of this week. Temperatures at 850mb are expected to rise to nearly 20°C today, which will result in daytime highs between 25-30°C through the second half of this week.

A weak low will move through Southern Manitoba on Thursaday night ahead of the main upper trough and while parameters don’t look too great for severe weather, a band of thunderstorms will likely develop in the late afternoon or early evening, intensify, and slowly move east-northeast. While tornadoes aren’t a likely threat with these storms on Thursday afternoon/night, CAPE values in the range of 1250-1750 J/kg combined with LIs near -5 and 20-30kt of bulk shear should provide enough for a threat of large hail. The slow-moving nature of the line of storms could potentially also produce a risk of locally heavy rainfall, with as much as 0.75-1.25” falling over a relatively short period of time. While showers will be commonplace over southwest Manitoba throughout the day on Thursday, the risk for showers does extend eastwards through the western and central Red River Valley in the afternoon. The bulk of precipitation will occur with the thunderstorms that develop in the evening, though.

This is still about 36 hours away, though, and things could change quite a bit between now and then. Models are having a hard time degrading the blocking pattern that’s in place right now, and some are much more progressive with features and some are much slower. If things end up more progressive than they look right now, there may be minimal storm threat for Thursday night.

Night 2 Thunderstorm Outlook

Thunderstorm Outlook for Night 2 (00Z to 18Z June 08).

Taking into account the various speeds, the current area that might see storms on Thursday afternoon/evening looks to be the area bounded from the US border north to Brandon, up towards Dauphin/Swan River, then eastwards across the Interlake and southwards down the eastern Red River Valley. Storms will exit through the Central/Northern Whiteshell. While the potential for heavy rainfall exists, I do not feel enough confidence in it to justify any slight risk categorization on the outlook. The storms will likely be marginally severe, though, so it’s important that they are not ignored with the prospect of even bigger storms on the weekend.

Friday looks to be another warm day; debris cloud left behind from Thursday night’s convection should clear bout by lunch time or early afternoon which will allow the sunshine to warm us up to the mid-to-high 20’s. Dewpoints will build through the afternoon pushing up to 18 or 19°C, making it feel quite humid. The main upper trough is set to move in on the weekend, though, and what a system it looks to be.

SPC Day 4-8 Outlook

SPC Day 4-8 Severe Thunderstorm Outlook

I’m not going to talk too much about Saturday’s setup yet, as it’s still a ways out and in this particular setup, the exact specifics are sure to change with every model run until it’s much closer. We’ll be under the influence of two strong shortwaves that will push copious amounts of instability over Southern Manitoba. CAPE values look to exceed 2500 J/kg and potentially be as high as 5000-5500 J/kg; this, combined with a weak cap north of the warm front and favorable shear profiles looks to point at a potent setup for severe thunderstorms with high probabilities of (extremely) large hail, strong winds, and elevated risks of tornadoes. The setup is similar to other tornado-producing setups of years past, including the Pipestone tornado of 2007.

We’ll have plenty of discussion about the upcoming storm threats in the comments, so be sure to check back often for the latest information about this weekend’s potentially dangerous storm outbreak.

Warm Start to June

After a warm weekend, which featured a beautifully Saturday and stormy Sunday, we will stick with warm to hot weather to start the week. A ridge of high pressure will gradually build into Southern Manitoba this week, allowing us to keep the warm conditions experienced on the weekend.

Upper ridge over Southern Manitoba

A ridge of high pressure is expected to build into Southern Manitoba this week

Monday will be a warm to hot day in Southern Manitoba, with high temperatures in the mid to high twenties under mainly sunny skies. Tuesday will again be warm and sunny day, with high temperatures in the low to mid twenties. An easterly flow pushing slightly cooler air into the province is the reason why Tuesday will be a bit cooler than Monday. Temperatures will climb again on Wednesday, as we reach back up into the high twenties under a south-easterly flow.

The weather through late week is, as usual, less certain. Thursday looks to remain warm but Friday into the weekend may be cooler. A low pressure system is currently forecast to cross Southern Manitoba on Friday, which will be a catalyst for cooler weather. More details will be available later in the week.

Trough over Western NA, Ridge over Central/Eastern NA

A trough will cause below-normal temperatures over Western North America (blue areas), while a ridge brings warmer weather to Central/Eastern North America (orange areas)

A quick update on the June forecast. Most long-range models are showing a ridge-trough pattern dominating North America through June. This pattern means a ridge will likely reside over Central/Eastern North America through a good part of June while a trough sits over Western North America. Southern Manitoba will be frequently caught in between these two features, causing our weather to be variable with hot spells as well as some cooler outbreaks. This pattern may also promote more chances for thunderstorms, though this is not as clear-cut.

At any rate, enjoy what will be a nice first half of the week!

A Chance of Showers Today, Mild Weekend Ahead

A weak trough pushing across SW Manitoba today will push into the Red River Valley this evening, bringing with it some scattered showers or thundershowers. Things will clear out quickly, and we’ll be looking at temperatures in the mid-20’s for the weekend.

GEMREG QPF for Friday Afternoon

Total expected precipitation from teh GEMREG model this afternoon.

We’ll have a slightly more unsettled day today as a weak surface trough pushes into the Red River Valley this afternoon. Temperatures will climb up to just over the 20°C this afternoon before showers and thunderstorms develop over SW Manitoba and push eastwards into the Red River Valley. Dynamics begin to fall apart as the afternoon progresses, and any showers or thunderstorms will struggle to survive in an increasingly disorganized environment. It looks like the best chance of seeing some rain this afternoon will be through the Western Red River Valley, with diminishing chances east of the Red River. By the time the trough gets to the Whiteshell, the threat of precipitation will likely be over.

Saturday looks to be a gorgeous day as sunshine once again dominates across Southern Manitoba and highs climb to around 25°C. Things will turn a little more unsettled overnight on Saturday as an area of rain blossoms over Southern Saskatchewan and heads our way. The exact location of the rain is still uncertain, however best indications are that we’ll see a cloudy day across much of the Red River Valley, with the bulk of the rain passing north of Winnipeg through the interalke region, with only a chance of showers for Winnipeg and areas south. It will certainly be a system to keep an eye on as the weekend progresses.