Tag: Thunderstorms

Unsettled Friday Leads Into A Hot Weekend

Brad Leave a comment

Notably warm and humid weather in place over Southern Manitoba today will bring a threat for severe thunderstorm activity across the region as a shortwave trundles through. An upper-level ridge will then begin to rebound back into the Southern Prairies in response to a digging trough off the western coast of North America, bringing even warmer air into the region thanks to the resultant southwesterly flow aloft that will develop.

Friday: Thunderstorms Possible Midday

A weak mid-level shortwave trundling across the region will bring a risk of thunderstorms to Winnipeg & the Red River Valley today[1] as warm and humid weather meets the colder air associated with the shortwave. As always, using our MIST principles:

  • Moisture: Adequate. Moderate moisture will be in place both at the surface and through the lower levels of the atmosphere as deep-layer moisture continues to build into the region.
  • Instability: Favourable. With both thunderstorm possibilities, both elevated and surface-based, enough instability will be in place. Surface-based convection would have greater potential to be severe, however it will rely on strong surface heating with mainly sunny skies until the shortwave arrives, which could be in question depending on what sort of nocturnal convection develops.[2] If it does end up cloudy, strong mid-level lapse rates associated with the shortwave should be enough to sustain showers or thunderstorms as it heads eastwards. All said, storms should have around 1000–2000J/kg of CAPE to work with, depending on their exact timing and where they’re based.
  • Shear looks quite good with around 35kt of 0–6km bulk shear and gently looping hodographs. Low-level winds are weak enough that tornado activity doesn’t look like a particular threat, but the directional shear is favourable for the organization of supercell thunderstorms.
  • Trigger: The shortwave moving through coupled with a weak surface trough will provide the convergence and trigger for convective initiation.
AWM Day 1 Convective Outlook
A slight risk of severe thunderstorms exists in the Red River Valley and southeastern Manitoba today.

All things considered, it’s likely that we’ll see some activity at some point today. The primary threats with today’s thunderstorms will be large hail and strong winds. Storm motions will generally be towards the southeast. Later in the day, a more organized heavy rainfall threat may develop with any storms still ongoing.

Those things aside, it will be quite a nice day. Temperatures will climb to around 28 or 29°C with a few clouds through the day. The humidity will begin to be more noticeable as dewpoints climb into the high teens by the afternoon ahead of the weak surface trough/low moving through. Winds will remain light.

Things clear out tonight with the humidity remaining in place and temperatures dipping down to about 17°C.

Hot & Humid Weekend Ahead

Temperatures will soar this weekend as warmer air moves into the region and sends daytime highs to 30°C or higher. Saturday will be a sunny day with a high around 30°C and dewpoint values in the high teens or low twenties making it feel more like the upper 30’s. Winds will be light. Expect a low near the 20°C mark on Saturday night.

Manitoba Health – Heat Alert Response System in Relation to the Heat Dial
This weekend could see provincial (pictured above) or federal responses to the heat and humidity over the region.

Sunday will see the daytime high climb even higher, most likely towards the 32 or 33°C mark as breezy southerly winds develop ahead of a developing low pressure trough. The humidity will remain in place with dewpoints in the high teens or low 20’s, making it feel more like the upper 30’s. There’s a slight chance we may see humidex values hit 40 on Sunday, which is Environment Canada’s criteria for a heat warning. That said, both Saturday and Sunday will likely qualify for the Province of Manitoba’s Heat Advisory and Response Pre-Alert which requires a humidex of 37 or higher.

There appears to be a slight chance late Sunday night or early Monday morning for some showers or thunderstorms to move through the area, but it looks very conditional at this point and it’s far to early to say much about it. We’ll put an update here early Sunday afternoon regarding the precipitation potential for Sunday night. Temperatures will likely only drop to around 19°C on Sunday night, however.

Long Term: Slight Cool-Down to Start Next Week

Looking ahead, it seems like we’ll see a slight cool-down next week as a frontal boundary stalls out over the region and brings a chance for multiple bouts of unsettled weather through the first half of the week. We’ll have more details about that bright and early Monday morning!

  1. Exactly when depends on the timing which will be affected by how much and what type of elevated convection developed with this feature overnight in Saskatchewan.  ↩
  2. If the nocturnal convection is in the right spot or strong enough, our sunshine could be replaced by cloud cover instead, dramatically limiting surface heating.  ↩

Summer Temperatures Return as Quiet Weather Continues

Brad Leave a comment

Temperatures will be returning to more summer-like values through the second half of this week thanks to an upper-level ridge that will push out the cold air drawn southwards behind this past weekend’s big storm and allow more heat to begin building into the region.

The coming two days will be gorgeous with plenty of sunshine, light winds and warm temperatures. Today will see daytime highs near 26 or 27°C while Thursday will bring highs a degree or two warmer. Overnight lows both nights will be near 12°C. The most significant weather feature will be the significant amounts of smoke that will be pushing into the region sourced from wildfires raging in the northwestern United States. At this point, it seems like it should mainly be aloft and not pose much of an air quality issue.

NAM Forecasted MUCAPE & Bulk Shear valid Friday evening.
The NAM is showing large values of CAPE (energy) and shear on Friday afternoon which suggests the potential for severe thunderstorms.

Friday will see a low pressure system moving through the region, bringing warmer temperatures alongside a thunderstorm threat. The major question mark, at this point, appears to be whether or not any smoke in the region inhibits temperatures from climbing high enough to trigger thunderstorms or not. That said, it looks like the potential will be in place for severe thunderstorms with over 3000 J/kg of CAPE expected and over 50 kt of bulk shear in place.

We’ll be taking a closer look at the severe thunderstorm potential on Friday morning in the next blog post, but for now, just keep aware that the threat for severe weather may return to the Red River Valley on Friday.

Other than the storm potential, daytime highs should sit near 30°C with mixed skies. There’s also a reasonable chance that it will be quite humid, making it feel more like the upper 30’s.

Heading through the weekend, it looks like Winnipeg & the Red River Valley will see highs near 30°C with plenty of sunshine, making up for the miserable weather during the last weekend. Other than the blip on Friday, there’s plenty of warm, dry and sunny weather ahead, so enjoy!

Weather Roller Coaster Ramps Up For The Weekend

Brad Leave a comment

A wild rollercoaster of weather conditions begins today as a fairly potent weather system develops today, rocketing temperatures close to the 30°C mark before things take a turn for the worse as a stormy transition sends daytime highs struggling into the low teens by the end of the weekend.

Friday: Another Beautiful Summer Day, Stormy End?

Today will be a gorgeous day as warm air surging northwards ahead of a developing low pressure system in the Northern Plains of the United States.  Temperatures will climb into the upper 20’s this afternoon under fairly sunny skies. Some cloud cover will start working into the region in the afternoon alongside a slight chance of showers as a weak mid-level disturbance rolls through. In the evening, a low-level jet (LLJ) begins to intensify as the low pressure system deepens and brings more lift into the region, spreading more cloud into the region.

850mb RDPS Temperature Forecast with Fronts & Low Level Jet Annotations
The RDPS is showing a warm front at 850mb just north of Winnipeg near midnight tonight. The LLJ is represented by the blue arrows and will be the trigger for thunderstorm activity tonight.

A round of thunderstorms is possible tonight along the nose of the LLJ.  The risk is somewhat conditional, dependent exactly how how much moisture is advected northwards within the LLJ. Assuming enough moisture is present to realize the instability, we head to MIST:

  • Moisture: This will be the most uncertain aspect of tonight’s thunderstorm potential.  Dewpoints at 850mb are forecast to be around 10°C, which should be enough to realize the elevated instability, however it’s a farily narrow ribbon, and if amounts are lacking a bit, convective initiation will struggle.
  • Instability: Fairly strong instability aloft will be present.  Models suggest mid-level (700 – 500mb) lapse rates of 7–8°C/km this evening, which would be considered quite strong.  If the expected moisture builds into the region, MUCAPE values of around 1000 J/kg should be realized.
  • Shear: The overall shear looks great, with widespread bulk shear values of 40–50kt expected over the Red River Valley this evening. The high bulk shear values are produced through a combination of strong velocity shear through the vertical coupled with large, looping hodographs indicative of favourable directional shear.
  • Trigger: Isentropic ascent of the LLJ as it overruns a warm front draped west-to-east along the international border coupled with falling heights ahead of the incoming upper-level low should provide a strong enough trigger to initiate convective activity.

All this combined means that there’s a fairly good chance of some thunderstorm activity through the Red River Valley this evening.  It likely won’t be severe; I think the higher threat for severe storms activity will be more in southwestern Manitoba where things will initiate earlier and rooted closer to the warm front.  That said, it certainly can’t be ruled out that there may be a rouge severe thunderstorm cell through the evening into the first half of the overnight period. Expect a low temperature near 17°C.

Mixed Bag On Saturday

There remains some uncertainty as to how Saturday will play out, but it seems quite probable that we’ll see some shower or thunderstorm activity through the day. There may be a few sunny breaks, but it should be cloudier than not through much of the day. If any rain manages to hold off until later in day, marginally severe thunderstorms could be possible in the Red River Valley, however it would be dependent on how much heating occurs (read: how sunny it manages to be). Even with decent heating shear looks marginal which will provide a barrier to significant thunderstorm development.

This comes with a caveat, however, as the forecast will be dependant on the timing of the cold frontal passage. With current best indications, there will be a slight risk of severe thunderstorms to the east of the Red River Valley on Saturday afternoon, however if the front slows down a little, that threat could shift westwards into the Red River Valley. We’ll take a closer look at it in an update tonight or tomorrow morning.

That said, temperatures will top out around 25°C with fairly light winds.

Saturday night will see the Red River Valley on the back side of the low and behind the cold front; colder air will begin pushing in alongside strengthening northerly winds. Expect a low near 13°C.

Miserable Sunday

Sunday will be a miserable day by any standard. Very cold air over the region—850mb temperatures are forecast to be a chilly 0–2°C—will keep our daytime highs to just the low teens. Very strong northerly winds will be in place over the region; sustained winds will likely reach 50–60km/h with gusts reaching as high as 80km/h or so. On top of all that, wrap-around precipitation will work it’s way across the Red River Valley, bringing more rain and/or showers to the region.

NAM Forecast 850mb Temperatures and Winds for Sunday Evening
The NAM is forecasting 850mb temperatures of 0-2°C and very strong northerly winds over the Red River Vallye on Sunday. Miserable.

To top it off, with lake temperatures near 21°C and 850mb temperatures forecast to be near 0°C, lake-effect or lake-enhanced rain/drizzle is probable in the lee of the lakes, persisting possibly into Monday morning.

The low temperature on Sunday night will be around 6 or 7°C.

Hopeful in the Long Range

The good news is that the long-range forecast looks good. Rather quickly behind the passage of this low, a broad upper-level ridge is forecast to begin building back into the Prairies. This will bring significantly warmer weather back to the region. Considering it’s still August and we’re talking about daytime highs in the low teens, a quick bounce back into the mid- to upper–20’s for daytime highs will be much appreciated.

Heat Wave Continues Until A Stormy Transition to a Cooler Sunday

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The heat wave across Southern Manitoba will continue through today and tomorrow as even more warmth and humidity build into the region. Significantly cooler air will move into the area on Sunday, behind a cold front passage on Saturday that will bring another round of potentially severe weather to the province.

Friday: Hot With Increasing Humidity

Today will be a hot day with increasing humidity as a deep southerly flow develops ahead of a deepening low pressure system ejecting northeastwards out of Montana. Temperatures will climb into the low 30’s with high temperatures reaching around 32 or 33°C this afternoon. Winds will also pick up out of the south to around 40km/h with gustiness on top of that. The humidity will be less than some days of late, but still fairly moderate with dew point values in the 18–20°C range. This will make it feel more like more like 37–40.

Some afternoon clouds will be about associated with the low pressure system lifting NE out of Montana. No precipitation is expected, though.[1] We’ll have a very mild low temperature tonight of 21 or 22°C.

Cold Front Brings Severe Weather Threat for Saturday

Saturday’s weather story will be dominated by a cold front pushing eastwards across the Red River Valley. The southerly winds combined with pooling ahead of the cold front will make for very humid conditions with dew point values climbing to 23–24°C. With a high temperature near 33°C, it will feel more like the low 40’s and make for very uncomfortable conditions. As the cold front pushes eastwards, showers and/or thunderstorms are quite likely.

AWM Day 2 Convective Outlook – Saturday August 15, 2015 to Sunday August 16, 2015
A moderate risk of severe thunderstorms exists through much of the Interlake, Red River Valley, and Whiteshell regions of Southern Manitoba on Saturday.

There are two possible outcomes for Saturday’s setup:

  1. Nocturnal advection develops in the Northern Plains of the United States and pushes northeastwards. Scattered showers and thunderstorms persist over the Red River Valley through much of the day before clearing out with the cold front.
  2. No or very little precipitation develops Friday night, leaving things dry and sunnier for Saturday. Severe thunderstorms would then be possible in the afternoon along the cold front.

At this point, it appears as if option 2 is the more plausible one. As always, looking at the MIST principles of thunderstorm development:

  • Moisture: Abundant. A deep layer of dew points ≥ 20°C will be in place over the Red River Valley, resulting in tremendous amounts of fuel for thunderstorms.
  • Instability: High. While the environment will be capped much of the day, significant instability will be in place through the mid- and upper-levels of the atmosphere. Steep mid-level lapse rates coupled with the high surface moisture will produce SBCAPE values in excess of 4000 J/kg and MLCAPE values of 3000–4000 J/kg.
  • Shear: More than enough. In general, a 40kt jet at 500mb over the region will combine with surface winds out of the south at 10–15kt to create around 25–35kt of 0–6km bulk shear. Hodographs show strong curvature, indicating likely supercell storm mode.
  • Trigger: The strong cold front pushing eastwards will provide focus for convection. While the capping inversion will hold surface-based convection back, the forcing from the frontal feature should be sufficient to initiate convection. 35–40kt southwesterly low-level jet may combine with steep mid-level lapse rates to produce elevated convection.

Given the extreme instability in place over the region (even elevated convection would have 1500+ J/kg of energy to work with), severe thunderstorms would be possible with either mode of convection. With the extremely high dew points in place, any thunderstorms that develop will be capable of torrential rainfall. Strong winds and large hail will be significant threats with any thunderstorms that develop. The threat of tornadoes cannot be ignored either; with strongly curved hodographs and such enormous amounts of energy, any supercell thunderstorms that develop would be capable of producing a tornado. The highest probability would be relatively close to the low pressure centre where the surface winds will be backed slightly more.

Saturday Severe Weather Update

Everything appears to be on track regarding today’s severe weather potential. There is a moderate risk of severe thunderstorms through much of the Red River Valley, Interlake and areas eastwards to the Ontario border. This includes large swaths of popular beaches & cottage country.

AWM Day 1 Convective Outlook for August 12, 2015
AWM Day 1 Convective Outlook for August 15, 2015

For the most part, all the expected conditions continue to pan out. Some elevated convection has developed overnight, however it doesn’t look like it will inhibit surface heating through the Red River Valley very much today. Very warm daytime highs in the low 30’s combined with dewpoint values in the 22-24°C range will combine to produce MLCAPE values of 2000-2500 J/kg and SBCAPE values exceeding 3000 J/kg. Combined with over 30 kt of 0-6km bulk shear and looping hodographs, there is sufficient energetics, dynamics and shear vectors to support strong supercell thunderstorms. Throughout the entire slight risk region, there will be a risk for large hail, strong winds and torrential downpours. Further north, in the moderate risk area, surface winds will be backed slightly more as the surface low pressure system continues moving northeastwards. Additionally, areas slightly further north will be closer to the upper-level jet and see enhanced 0-6km shear values. As such, any thunderstorms that develop in this region will pose a tornado threat, with the possibility of the production of a significant tornado today.

A strong cap in place will keep surface-based convection from triggering until late in the day as a trough pushes eastwards into the Red River Valley. Discrete supercell thunderstorms will likely develop between 4 and 6PM and then push east-northeastwards. As the line of thunderstorms pushes eastwards, upscale growth is likely as the system evolves into an MCS capable of all modes of severe weather.

Today could end up one of the most significant thunderstorm days of the year in Southern Manitoba. Stay aware of any watches and warnings issued by Environment Canada through the day today.

Sunday: A Cool Clean-Up

Sunday will bring partly cloudy skies on the back-side of the low as it departs Manitoba. Significantly cooler weather will be in place with daytime highs of just 23°C expected. There may be a slight chance of some light, isolated showers, but the threat looks minimal at this point. Temperatures will dip to around 12°C on Sunday night.

Next Week? Quick Rebound

Taking a quick peek at next week, it appears that the cool down will be short-lived as significantly warmer air begins pushing back into the region mid-week. Alongside the warmer temperatures will come the potential for more unsettled, stormy weather.

  1. A few showers may drift towards the Red River Valley from the NW this morning, however they should dissipate before it reaches our region.  ↩