Scorching Summer Weather Sizzles Southern Manitoba

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.  ↩
RDPS Surface Temperature Forecast – 00Z Tuesday July 21, 2015

Pleasant, Sunny Conditions to Start the Week

Tired of the phrase “chance of a thunderstorm” and want to just have a couple days without rain? Good news! It looks like Winnipeg & the Red River Valley will finally shake the unsettled weather pattern and see a couple days of calm, pleasant summer weather with very little chance of precipitation thanks to an upper-level ridge that will build into the Eastern Prairies.

The coming few days will see gradually warming as we transition from the cool air mass left behind from the systems that tracked across the region on Saturday & Sunday into a warmer air mass pushing in from the west. Today will be the coolest day with a daytime high of just 22 or 23°C under partly cloudy skies. There may be some isolated shower or thundershower activity, but at this point it looks like it would be very spotty in the Red River Valley. Temperatures will dip to around 12°C tonight.

Tomorrow and Wednesday will both be beautiful summer days with highs climbing into the mid-to-upper 20’s under mostly sunny skies. Winds look fairly calm, although by Wednesday afternoon we could see southerly winds begin to strengthen. At this point it doesn’t look too bad – perhaps 30km/h with some gustiness on top of that – but if the pattern speeds up a bit, we could end up seeing quite windy conditions out of the south by then. Conversely, if the entire pattern is a bit slower we’ll see calm conditions throughout the day. Overnight lows both nights will be in the low-to-mid teens.

Hot, Humid & Stormy Weather Returns for End of Week

Looking ahead into the second half of the week, the trend seems to be for the hot and humid weather to return. As the upper ridge transitions across the region, deep layer southerly winds developing will tap into more humid air to our south and begin increasing the dew point. By Thursday evening, the dew point could be as high as 20–22°C, making it feel very sticky out there. Depending on the exact daytime highs, Thursday and Friday could both end up feeling more like the mid-to-upper 30’s instead of the upper 20’s thanks to the humidity.

GDPS Surface Dew Point Forecast – 00Z Friday July 24, 2015
The GDPS is forecast dew point values climbing into the 20-22°C range by Thursady evening.

In addition to all that heat and humidity, a low pressure system tracking through at the end of the week looks to bring the potential for strong to severe thunderstorms, likely on Thursday. More on that later this week!

Summer Warmth Arrives

Summer-like warmth has arrived for Winnipeg and the Red River Valley thanks to an upper-level ridge moving into the region that will spread warm air over Manitoba for the coming days. Some rain looks likely on Thursday evening as a “cool” front passes, but the other days through the second half of the week look beautiful with plenty of sun to go along with the warmer weather.

Today will be a mainly sunny day with a high near 21°C. Winds will remain fairly light through the day as well. With an overnight low near 8°C or so, the warmth should hang on into the evening making for a pleasant evening to be outside.

Thursday will bring a fair amount of cloud, however the sun will still poke out a few times through the day. Winds will be breezy out of the south, picking up to around 30–40km/h with gusts to 50–60km/h or so. Heading into the second half of the afternoon should really bring in the thicker cloud ahead of the approaching “cool” front. A band of showers will move in sometime between 6–9PM and last for a few hours as they move through.

RDSP 12hr. Precipitation Accumulation
The RDPS shows around 2mm of rain through much of southern Manitoba associated with the passage of a “cool” front on Thursday evening. Image above is total accumulations from Thursday evening at 7PM to Friday morning at 7AM.

Precipitation is expected to be fairly light, however, with total accumulations around 2mm, although if the odd convective cell gets going, some places may see closer to the 5mm mark. Winds will taper off with the passage of the front and temperatures will drop to around the 7°C mark with clearing skies overnight.

Friday will be another pleasant day with light winds, mainly sunny skies and a high near 21°C. Expect a low near 8°C on Friday night.

Beautiful End to the Long Weekend

The Thanksgiving long weekend will end on a nice note, with mild temperatures and sunny skies for holiday Monday.

Holiday Monday will be pleasant in southern Manitoba
Holiday Monday will be pleasant in southern Manitoba


16°C / 4°C
Mainly sunny

Today will be very nice in southern Manitoba. Temperatures will be in the mid teens with light winds and sunny skies. This pleasant weather is the result of a ridge of high pressure building over the Prairies, which will continue to bring mild conditions to Manitoba for much of the week.


17°C / 7°C
Increasing cloudiness

Tuesday will be another nice day in southern Manitoba as temperatures climb into the upper teens. A gusty south wind will develop by late in the day, but otherwise it should remain quite pleasant. There will be an increase in cloudiness through the day, as some upper-level cloud cover begins to spill into Manitoba from the west.


19°C / 10°C
A few clouds

Wednesday will see a continuation of the warm weather from Monday and Tuesday. However, there will also be a very stiff south wind, making it feel a bit chillier than it would otherwise be. Temperatures will nonetheless be in the upper teens or near 20C, which is of course well above normal for this time of year.

Long Range

A cold front is currently forecast to pass through southern Manitoba on Thursday, ushering in cooler conditions to end the week. However, models have been strongly hinting at a return to above-normal weather by next week, a trend that may last through the end of the month.