Tag: Severe Thunderstorms

Heat Wave Continues Until A Stormy Transition to a Cooler Sunday

Brad Leave a comment

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.  ↩

Scorching Summer Weather Sizzles Southern Manitoba

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Temperatures will soar into the low 30’s over the coming days as a broad upper-level ridge continues to build across the Canadian Prairies, bringing with it some of the warmest temperatures of the year. Alongside the heat will come several bouts of humidity; at times over the coming days, humidex values – a “feels like” temperature that combines the effects of heat and humidity – will approach or exceed 40, making for exceptionally sweltering weather. In addition to the heat and humidity, today will bring a risk of severe thunderstorms…if they’re able to develop this afternoon.

Wednesday: Hot, Humid & Significant Thunderstorm Risk

Today will be a scorching hot day that will be made oppressively hot by the increasing humidity through the day. Temperatures will soar quite quickly today with the mercury reaching around 30°C by lunch time and then climbing a few more degrees above that this afternoon. All the while, the dew point will climb to the 19–20°C mark, resulting in humidex values in the 37–41 range for much of the day.

The biggest weather story for today, though, is the thunderstorm potential. First, here’s our outlook for today, but the discussion is important, so don’t skip over the rest!

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

A slight risk of severe thunderstorms exist across the Red River Valley, the Interlake region and eastwards to the Ontario border. Any storms that manage to develop today will have the potential to become very potent storms capable of all types of severe weather, including tornadoes, however there remains a single big question: will there be any storms?

As always, lets take a look at the basic MIST principles of thunderstorm forecasting:

  • Moisture: Ample moisture will be in place as surface dew point values climb to 20°C. 30mb mixed layer dew points are also expected to be in the high teens, which will make for ample fuel availability in convection.
  • Instability: Instability is strong but conditional. Given the high moisture values, MLCAPEs will sit in the 2000–2500 J/kg range while SBCAPE values may exceed 3000 J/kg. The crux is, however, the capping inversion. Strong insolation will chip away at the cap through the day, however 30–50 J/kg of inhibition will likely remain.[1] The big question is, will the combination of surface trough and lake breeze interactions provide enough lift to break the cap? If any storms do manage to initiate, it’s all clear for explosive growth in a strongly unstable environment.
  • Shear: Shear looks fantastic for the development of strong, sustained supercell thunderstorms. 0–6km bulk shear values are expected to be in the 30–35 kt range while hodographs show excellent curvature. No questions exist about how favourable the shear is for supercell thunderstorm development.
  • Trigger: As mentioned above, two triggers will be in place today. The first is a trough line pushing through the Red River Valley & Interlake this afternoon. The second will be various surface boundaries developed through differential heating on escarpments (RRV, Gunton Bedrock) or lake breezes. It’s only slightly likely than any one of these features would be able to provide enough lift to trigger a thunderstorm, however if two or more of these features interact, it could trigger thunderstorm development. The trigger is the biggest uncertainty with today’s thunderstorm potential.

All these factors together combine to give a slight risk of severe thunderstorms across a wide region of Southern Manitoba. Despite the “lower” threat classification, all types of severe weather – flooding rains, large and damaging hail, severe wind gusts, tornadoes – are possible in thunderstorms in the Red River Valley today. The slight risk is given not for thunderstorm intensity – any thunderstorms that develop today could be very, very strong – but rather for the uncertainty associated with if they’ll even occur and expected isolated nature of the storms.[2]

On tornado potential: Today brings with it a non-zero tornado threat, particularly for areas in the northern half of the Red River Valley and southern sections of the Interlake region. Hodograph curvatures are very impressive, and when storm-relative values are taken into account, helicities will be quite high in any thunderstorms that manage to develop. Cloud bases will be fairly high, but high dew points should help diminish significant evaporative cooling below the cloud base. Numerous parameters show favourable environments for thunderstorms capable of producing tornadoes as well. It’s impossible to forecast a tornado this far in advance, but if you live in the slight risk area, it would probably be wise to keep up to date on any watches/warnings issued by Environment Canada.

Temperatures will dip to around 19°C tonight with slightly less humid conditions.

Thursday: A Brief “Cool Down”

Marginally cooler air works into Southern Manitoba behind Wednesday’s trough line which will be reflected in daytime highs a whopping 1–3°C cooler, but still likely at 29–30°C or a touch warmer. Perhaps the bigger difference will be more tolerable humidity levels as dew point values drop into the low teens by the end of the day. Skies will be mainly sunny with relatively light northwesterlies as a ridge of high pressure builds in.

Winds shift southerly in the evening as the Red River Valley moves onto the back-side of the surface ridge and warmer air begins to push in again. Expect a low near 16°C.

Friday: Don’t Worry, It’s A Dry Heat

The heat is back on Friday with daytime highs climbing back to around 33–34°C. It won’t feel as hot as Wednesday, however, thanks to significantly lower dewpoints in the low- to mid-teens. While we’re not talking Arizona desert heat, it’ll be far more comfortable than the 20°C dew points earlier in the week.

Heading into Friday night, deep-layer moisture transport ramps up and will begin bringing significant amounts of moisture into the region aloft. This, combined with warmer air moving in, will lead to a fairly balmy night with lows near the 20°C mark.

Long Range: Severe Storm Threat Returns on Saturday

It looks like a threat of severe thunderstorms returns to Winnipeg & the Red River Valley on Saturday. Very humid conditions with highs in the upper 20’s will clash with a cold front moving in from the west. Showers and thunderstorms are probable with this front, and with significant energy and shear in the region, it’s entirely possible for severe thunderstorms to develop. It will all depend on the exact strength & timing of the cold front, so we’ll take a closer look at that on Friday when the event is closer.

Sunday will be a comparatively cold day with partly cloudy skies, a bit of a breeze and highs in the low 20’s.

  1. Many studies show that some of the strongest supercell thunderstorms form in environments with between 25–50 J/kg of inhibition.  ↩
  2. At this point, we’re not expecting a huge line of thunderstorms to roll across the Red River Valley; rather it seems probable that there would be just one or two very strong storms.  ↩

Severe Thunderstorm Threat Returns

Brad Leave a comment

A threat of severe thunderstorms returns to Winnipeg and the Red River Valley today as a cold front advances eastwards into a hot, increasingly humid air mass that has been building into the region over the past few days.

Friday
29°C / 16°C
Afternoon/evening thunderstorms. Slight risk of severe thunderstorms.

Saturday
28°C / 18°C
Mainly sunny

Sunday
29°C / 17°C
Mixed skies; chance of showers or thunderstorms

Before thunderstorms develop this afternoon, we’ll see another hot summer day. We’ll see temperatures climb towards the 30°C mark with a fairly breezy wind out of the south at 40-50km/h. A fair amount of smoke will still be lingering aloft, so temperatures may struggle getting those final couple degrees towards the 30 mark.

Thunderstorms will develop this afternoon along the cold front through the western Red River Valley and Interlake and push eastwards. We’ve assessed a slight risk for severe storms from the MIST assessment:

  1. Moisture: Surface dewpoints will climb into the high teens today and although they are forecast to drop off somewhat through the boundary layer, there should be ample moisture in place for storm development.
  2. Instability: A capping inversion will keep things fairly quiet through much of the day today. Moderate mid-level lapse rates will develop through the day (possibly enhanced by the EML[1] from Saskatchewan’s overnight convection). Low-level instability will be somewhat limited today by diminished heating due to cloud cover and smoke aloft, however temperatures in the upper 20’s will come very close to breaking the cap.
  3. Shear: Looks very good. Around 30kt of surface to 6km bulk shear will be in place which will support organization of thunderstorms. 0-2km shear values of around 20-25kt reflect the moderate veering of the winds that will exist through the lower levels of the atmosphere and will support the development of supercell thunderstorms early in the event. As the storms mature, shear becomes more linear and will help support the development of a squall line.
  4. Trigger: Check! A strong cold front with good convergence will either erode the cap to initiate thunderstorms or provide enough forcing to overcome the cap.

Once thunderstorms develop this afternoon, they will likely quickly organize into discrete supercells capable of all modes of severe weather[2]. More unidirectional shear above 850mb will marginalize the tornado threat as more energy will have to be expended to develop the mesocyclone through the vertical, but with potentially as much as 2500-2700J/kg of MLCAPE, tornado(es) cannot be ruled out given the wind profile.

A slight risk of severe thunderstorms is possible over south-central and south-eastern Manitoba this afternoon into the evening.
A slight risk of severe thunderstorms is possible over south-central and south-eastern Manitoba this afternoon into the evening.

Storms will then increase in coverage and develop into a line along the cold front. Severe weather will still be possible, although the primary threats will shift to damaging winds and large hail. With strong unidirectional shear profiles through the Interlake, the development of bowing segments giving damaging winds is possible through that region.

The thunderstorms will push off into southeastern Manitoba this evening with a continued severe weather threat before tapering off in northwestern Ontario overnight. Winnipeg will see clear skies and a low around 16°C.

Mixed Weekend

Saturday will be a fairly pleasant day with weak ridging producing mainly sunny skies with light southerly winds and a high near 28°C.

Clouds will push in on Saturday night as we drop to a low around 17 or 18°C. There is a very slight chance of a shower or thundershower in the overnight period.

Sunday will be another warm day with a high close to 30°C under mixed skies. The afternoon will bring another chance for showers or thunderstorms as a trough line works into the province.

  1. Eleveated Mixed Layer  ↩
  2. Torrential rain causing localized flash flooding, large hail in excess of 20mm, damaging wind gusts in excess of 90km/h, and/or tornado(es).  ↩

Late-Season Thunderstorm Risk Kicks off Dreary Weekend

Brad Leave a comment

A powerful low-pressure system pushing northwards out of the Dakotas that will bring copious amounts of rainfall to SE Saskatchewan and Western Manitoba will also bring a risk for thunderstorms, perhaps even an isolated severe thunderstorm, this evening in advance of an occluding cold front. This will mark the start of a somewhat dreary weekend for the Red River Valley that will be marked most notably by a wet & windy Saturday and a very cool, albeit sunny, Sunday.

Thunderstorms Possible Today

Friday

19°C / 12°C
Mainly cloudy. Chance of showers with the risk of a thunderstorm late in the day.

We’ll see a mainly cloudy day today with relatively nice temperatures as we sit in the warm sector of the low pressure system pushing into the province. Despite the cloudy weather, we should see temperatures climb to around 19–20°C for a high with south-easterly winds to around 30km/h.

We may see a shower early this morning as the warm front pushes through and brings us into the warmer air, although a majority of the activity will be off to our west. If anything manages to push into Winnipeg, it will be relatively short-lived. After that we’ll see no chance of precipitation until later in the afternoon or the evening as a cold front begins pushing into the Red River Valley from the south.[1]

Event outlook for Friday, October 11th.

Event outlook for Friday, October 11, 2013.

While we sit under cloudy skies, this would be a good time to note that the weather to our west will be decidedly different. Rain will push in early this morning and spread NNE through the day, hitting areas west of the Red River Valley and Lake Manitoba the hardest. In total, anywhere from 35–75mm of rain is expected, with the lesser amounts closer to the Red River Valley and the higher amounts running along the Saskatchewan border then towards Lake Winnipegosis with enhanced precipitation near the Riding Mountains as upslope enhancement in the north-easterly winds amplifies the amount of rain. Environment Canada has rainfall warnings out for many regions in Western Manitoba, and you can check here to see if your region is covered by one and find additional details.

As the cold front approaches the Red River Valley this evening we’ll see considerable destabilization of the mid-levels coupled with an extremely strong 60–70kt 500mb jet beginning to poke it’s nose north of the border. The Red River Valley will lie in a fairly diffluent area aloft with strong convergence along the cold front as it pushes northwards. Limited surface moisture will constrain SBCAPE values to only a mere 400–500J/kg, but the extremely strong dynamics, in particular the strong directional and speed shear, may help promote the growth of strong-to-severe thunderstorms along/just ahead of the cold front.

This all is highly dependant on either enough destabilization occurring or enough convergence occurring along the cold front. At this point, I think that the southern Red River Valley will see the strongest storms with a lesser risk of strong storms further north here in Winnipeg. By the time the front reaches us, it seems like it will be a band showers and/or thunderstorms with less organization than when things initiate in the Dakotas. If any of the storms do become severe, the main threats will be large hail and strong winds. There will be a very small risk of a few weak tornadoes with these storms, but I believe that will be most likely in North Dakota with the odds diminishing fairly rapidly as you push northwards through the Red River Valley.

The showers/thunderstorms will push through overnight as we drop to a low of around 11 or 12°C.

Wet & Windy Saturday

Saturday

↘ 6°C / 2°C
Cloudy with showers. Windy. Temperature dropping through the day.

Saturday in Winnipeg will be marked by wet and windy weather as we move onto the back-side of the Colorado low and see some wrap-around rain and gusty northwesterly winds move in.

The rain will likely be somewhat showery in nature – in that we won’t see solid rain all day long – and there’s some uncertainty on how much we’ll see exactly, but around 5mm seems like a relatively safe bet at this point. If the system is a little faster than forecast we could end up with almost nothing as the rain would fall further north, and if it’s slower than forecast we could see closer to 10mm as we end up under the wrap-around rain for even longer.

The wind will be the main weather story though. Here in Winnipeg we’ll see winds 30–40km/h out of the northwest with gusts up to 60km/h, but it will be a significantly different story for those on the lakes. Winds over the lakes will increase to nearly 50–60km/h on Saturday with gusts as high as 90km/h, which will produce fairly sizeable waves. If you have a home or cottage on the southern or eastern shores of the lakes, you’ll want to make sure you make any preparations you might have to and prepare for some strong wave action and howling winds for Saturday and Saturday night.

With those strong winds will come falling temperatures; here in Winnipeg we’ll likely see temperatures fall to around 5 or 6°C by the end of the day as colder air pushes in on the back-side of the low. Skies will clear and winds will lighten overnight as we drop to around 2°C for our overnight low.

Sunny but Cool Sunday

Sunday

9°C / -2°C
Sunny. Cool.

Sunday will see the return of the sun, but the price we’ll pay is significantly cooler weather than we’ve been having over the past week. Daytime highs on Sunday will top out at only 9 or 10°C and it will be a slow climb to get there. Temperatures will likely drop well below 0°C on Sunday night with a hard frost likely as temperatures dip to around –2°C.

This will also mark the transition into a cooler pattern. Daytime highs will remain around 10°C through much of the week.

  1. It sounds odd, but this system is essentially sideways with the warm front and cold front both moving from south to north.  ↩