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

Brad Leave a comment

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.  ↩

Summer Heat Wave Building In

Scott Leave a comment

A summer heat wave is on the way as a strong upper ridge builds over the Prairies. Winnipeg will likely see 30°C at least once by mid-week.

Monday

Today will feature increasingly cloudiness through the day as convective clouds develop with daytime heating. We may see a few showers or thunderstorms develop as these convective clouds grow, but any storms will be non-severe. Other than the chance of a shower, it will be a pleasant day with highs in the mid twenties and light northerly winds.

Tuesday

Tuesday will be one of the warmest days we’ve seen in a awhile as high temperatures climb up to the 30C mark in much of southern Manitoba. Skies will be mainly sunny and winds will be breezy from the south. It appears that the humidity will increase somewhat with the push of warmer air, but not too oppressive levels.

An upper ridge over western North America will bring warm weather to southern Manitoba this week
An upper ridge over western North America will bring warm weather to southern Manitoba this week

Wednesday

Wednesday should be the warmest day of the week with high temperatures climbing into the low thirties. Some weather models even suggest we may reach the mid thirties, but that remains to be seen. Humidity levels should edge up further on Wednesday, to uncomfortable levels. Humidex values will likely be near 40 in most areas by late afternoon. This higher humidity will also help to create a risk of thunderstorms on Wednesday. At this point it appears severe storms will be possible, but we’ll provide another update as the risk gets closer.

Long Range

The long range forecast suggests we’ll continue to see frequent periods of hot weather through mid August. However, it doesn’t look like the hot weather will be in place continuously, with frequent surges of cooler air breaking up warmer periods. The long range forecast also shows a fairly active storm track through our region, so there will likely be a fairly frequent risk of thunderstorms and precipitation over the next while.

Typhoon Soudelor Takes Aim at Taiwan and China

Matthieu Leave a comment

A tropical disturbance that was once a powerful super typhoon over the open waters of the Western Pacific earlier this week has now slightly weakened and is taking aim at southeastern Asia.

As of Friday night Soudelor was a typhoon of strength equivalent to a category two hurricane and had just made landfall on Taiwan’s northeast shores. The typhoon packed sustained winds of about 170km/h gusting to over 200km/h Friday night as it made a direct landfall on the island of Taiwan. The biggest threat with the typhoon, however, was rainfall. Taiwan’s rugged terrain meant that orographic lift (lifting of air pushed up the mountains) would greatly enhance precipitation amounts, especially on the north side of the island. Models showed that as much as a metre of rainfall (or more) could fall before it is all said and done.

Visible satellite image of Soudelor at sunrise late Friday evening (our time). (Source: Himawari Sat.)
Visible satellite image of Soudelor at sunrise late Friday evening (our time). (Source: Himawari Sat.)

The effects of typhoon Soudelor are still uncertain as of Friday evening but the Taiwanese authorities reported that there were over 2.6 million residents without power, wreaking havoc on day to day activities as well as travel in the region. In addition to that, as of Friday night there were four confirmed deaths associated with the typhoon, two of which were associated with the storm surge which had the biggest impact on the northeast shoreline. The station that clocked the highest rainfall amounts as of Friday evening was the town of Taipingshan, which was already well over a metre of rainfall (1,241mm). Taipei, which is less than 50km from this town, had already recorded an astonishing 500mm in some parts of the city.

Conditions are expected to continue to be poor until later today, as the heavy rains are expected to continue to fall in the northern half of the country. Soils will become saturated, if not already, and overwhelmed by the rainfall, resulting in mudslides in the mountainous regions – a region of Taiwan which is known to be very prone to these types of disasters. Soudelor’s effect on China isn’t expected to be as severe, but heavy rain/flooding will once again be the main threat as the tropical system moves over China’s mainland and begins to weaken.