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Unsettled Weather Brings Seasonal Cool-Down

September 16, 2015September 16, 2015 Brad Leave a comment

After a pleasant, summer-like start to the week, the weather is set to turn more unsettled as a disturbance rolls through Southern Manitoba tonight. Fortunately, the agitated weather will only bring temperatures back towards seasonal values before we see the heat move back in through the weekend, setting Winnipeg & the Red River Valley up for a hot start to next week.

Today will be a fairly pleasant day in the Red River Valley. There’s a slight chance of some shower activity early this morning as a trough passes through the region, but afterwards we’ll see the cloud begin to clear out through the remainder of the morning leading to just a few clouds this afternoon through the region. Daytime highs will climb to around 21°C–but with significantly less humidity than yesterday–with winds initially out of the northwest at 20–30km/h tapering off through the morning.

The more significant weather will roll into the province this evening as a low pressure system lifts northeastwards out of North Dakota and pushes across southern Manitoba. An area of showers, likely with thunderstorms embedded, will develop across southern Saskatchewan and northeastern Montana and spread eastwards through the night, pushing into southwestern Manitoba early in the evening and then spreading into the Red River Valley and Interlake through the remainder of the night. As is typical with systems that involve convection through the night-time hours, model solutions are a little scatter-shot as to what the outcome will be. Overall, it appears that the bulk of the precipitation will pass to the north of Winnipeg, however some models are coming up with solutions that bring significantly more precipitation into the region.

NAM Forecast Simulated RADAR Reflectivity valid 12Z Thursday September 17, 2015 — This simulated RADAR image from the NAM forecast valid on Thursday morning shows a band of heavy, convectively-driven rain over Winnipeg & the Red River Valley.

The NAM-based solutions all tend to produce fairly strong, convectively-driven rainfall over the Red River Valley late tonight into Thursday morning. With PWAT[1] values near 35mm, the rainfall could be quite intense, however strong winds aloft should be moving anything that develops along at a fairly decent clip, meaning overall rainfall accumulations shouldn’t be excessive with around 10–20mm in any heavier precipitation that develops. Outside of thunderstorms/heavy rain cells, the more general rainfall amounts from this system should be around 2–5mm or so in regions south of the Trans-Canada Highway, and closer to the 5–10mm range for areas northwards.

NAM Forecast Sounding for Thursday Morning — This forecast sounding for Winnipeg from the NAM for Thursday morning indicates heavy rain or thunderstorms may be possible.

Temperatures will dip to around 14°C tonight. Thursday will see a high near 15°C with winds increasing out of the northwest to 40 gusting 60km/h in the afternoon. A chance for showers will persist through the remainder of Thursday under mainly cloudy skies.

Friday will bring calmer weather to the region with mainly sunny skies and a high near 19°C. Winds shouldn’t be too bad at around 15–20km/h.

Warmer Weather Returns on the Weekend

Our cool-down to seasonal temperatures will be short-lived, however, as warmer weather is set to build back into Manitoba through the weekend. The upper-level trough that will bring us our unsettled weather will push off to the east and a zonal flow is forecast to quickly develop across the Prairies, pushing in warmer air aloft that will begin to bump our temperatures back upwards. Saturday looks to have a high around 20°C, while Sunday will see the mercury climb towards the mid–20’s.

GPDS Forecast 850mb Temperatures valid 12Z Monday September 21, 2015 — This forecast of 850mb temperatures from the GDPS shows temperatures pushing into the upper teens on Monday morning.

The GPDS is forecasting 850mb temperatures pushing into the upper teens through Monday, which would equate to temperatures in the upper 20’s as long as we see the sunshine. Afterwards, it looks like we may see a couple more disturbances roll through in the remainder of the week, bringing temperatures back towards seasonal.

While we will have occasional cool-downs, long-range forecasts continue to forecast above-normal temperatures through the remainder of September.

Precipitable Water ↩

Stormy Start to An Unsettled Weekend

September 4, 2015September 3, 2015 Brad Leave a comment

Friday will bring a severe thunderstorm threat to Winnipeg & the Red River Valley as the first of several bouts of unsettled weather moves through, gradually flushing out the unseasonal heat and humidity and transitioning us towards almost fall-like weather.

Friday

29°C / 18°C

Mainly cloudy; showers and thunderstorms this afternoon

Saturday

24°C / 17°C

Mainly cloudy; slight chance of showers. Evening showers or thunderstorms possible

Sunday

24°C / 11°C

Mainly cloudy; slight chance of drizzle or light rain

Mainly cloudy skies will be over Winnipeg & the Red River Valley today while a low pressure system gather steam and begins to move into the region from North Dakota. Little in the way of weather is expected until the low approaches this afternoon and triggers a substantial amount of convective activity. Showers and thunderstorms are expected to fire up mid-afternoon and track to the northeast. There’s a decent chance that the stormy weather will persist well into the evening before it clears out and moves off to the northeast.

AWM Day 1 Convective Outlook — A slight risk of severe thunderstorms exists over south-central and southeastern Manitoba today.

A slight risk for severe thunderstorms will be in place over much of south-central and southeastern Manitoba today. Looking at the MIST basics for thunderstorms:

Moisture will be ample with deep boundary layer moisture evident through surface dewpoint values near 22°C thanks to a multi-day build-up of humidity in a southeasterly flow. Strong evidence of the substantial moisture in place is shown by the precipitable water values which are forecast to climb over 50mm through the afternoon.
Instability will moderate with MLCAPE values around 2000–2500 J/kg. Much of the instability will be brought through the substantial moisture present since mid-level lapse rates are only expected to be moderate and not excessively steep.
Shear will be ample with approximately 25–35kt of 0–6km bulk shear and broadly looping hodographs. This should support the development of organized thunderstorms.
Trigger: there will be several triggers converging on the Red River Valley this afternoon including a frontal boundary, approaching low, as well as shortwave aloft. There should be no troubles finding something to trigger thunderstorms.

The primary threats from today’s storms will be heavy rain and large hail. PWAT[1] values are expected to climb over 50mm, which means torrential downpours and flash flooding will be a notable threat with this afternoon’s thunderstorms. Additionally, with such high MLCAPEs and adequate storm structure through the shear profiles, large hail may be an issues, however that would likely be a more isolated threat than the rainfall.

The thunderstorms will gradually push off to the northeast. Total storm rainfalls may exceed 2–4” (50–100mm) in some places, while other areas may end up seeing very little. Be sure to stay alert for any watches or warnings issued by Environment Canada.

Less excitingly, daytime highs will sit around 29°C today (which will feel more like the upper 30’s thanks to the humidity) with winds out of the southeast at 20–30km/h. Expect a low near 18°C.

Cooler, Unsettled Weekend

Both Saturday and Sunday will be cooler days with highs in the mid–20’s. Some uncertainty exists on precisely how things will play out, but in general, a very powerful low pressure system is expected to develop and lift northwards through Saskatchewan through the weekend.

The biggest change, compared to Friday, will be that it seems like the timing for any precipitation will shift from daytime hours towards the evening and overnight hours. Saturday will be mainly cloudy with just a very slight chance of some showers through the daytime hours. As the evening approaches, though, it looks likely that thunderstorms will develop along the western escarpment of the Red River Valley and then progress eastwards across the valley overnight. At this point it looks like the storms will be non-severe, but we’ll keep an eye on them in case the threat increases as we get closer to the event.

The overnight low on Saturday night will be around 17 or 18°C.

Sunday will be another fairly cloudy day with a slight chance of some very light rain or drizzle as easterly winds keep the boundary layer socked in moisture while drier mid-level lift approaches. As the evening approaches, once again some showers or thunderstorms are possible. Expect a low in the low teens on Sunday night.

Next Week’s Weather?

At this point, next week looks much cooler and drier with more fall-like weather in place. Daytime highs through the first half of the week look to be in the 15–20°C range while overnight lows will drop towards the mid-single digits. Little precipitation is expected, and we’ll see more and more sun as the week progresses.

PWAT stands for precipitable water, a measure of how much water is contained in a column of air. ↩

Sweltering Heat Moves Into Manitoba

September 2, 2015September 2, 2015 Brad Leave a comment

The coming days will be marked by a rare late-summer heat wave that will see hot and humid conditions moving into the Red River Valley, sending humidex values soaring towards the low 40’s. The hot weather will be relatively short-lived, though, as a cold front moving into the region on Friday will send temperatures back towards seasonal values alongside a returning chance for showers or thunderstorms.

Today and tomorrow will both be swelteringly hot days with daytime high temperatures in the low 30’s throughout Winnipeg & the Red River Valley. Humidity will increase dramatically this morning as temperatures begin to warm and the boundary layer deepens and taps into a significantly more humid air mass that’s moved in aloft overnight. By mid-to-late morning, dewpoint values will have climbed into the high teens or low 20’s across the Red River Valley. Combining the high dewpoints with the hot daytime high temperatures, humidex values in the upper 30’s to low 40’s are expected. Environment Canada has issued a heat warning for Winnipeg as well as many other areas across Southern Manitoba including the southwestern corner, Red River Valley, and southeastern Manitoba. Thursday will be slightly warmer and more humid than today is as both the temperature and dewpoint are expected to climb another degree or two higher.

RDPS Forecast Humidex valid the afternoon of Thursday September 3, 2015 — The RDPS is forecasting a large swath of humidex values over 40°C (orange) in Manitoba on Thursday afternoon.

With such substantial humidity in place, overnight lows both tonight and tomorrow night will be quite warm, bottoming out near the 20°C mark. Additionally, expect just slightly breezy winds out of the south.

Friday will bring increasing cloud through the day as a cold front approaches from the west. Temperatures should manage to climb into the upper 20’s before the cloud cover cuts off our daytime heating. At this point, it looks quite likely that a large are of showers and thunderstorms will work their way across the Red River Valley through the afternoon. Severe thunderstorm potential looks minimal at this time, but we’ll keep an eye out and issue and outlook if it seems like it might pose more of a threat. Temperatures will cool down into the mid-teens on Friday night with clearing skies.

Summer Isn’t Over Yet!

August 31, 2015August 31, 2015 Scott Leave a comment

We’ll see more summer-like weather this week in Winnipeg and across the Red River Valley as it continues to feel more like July than the beginning of September.

Monday

Today will start out mainly cloudy as a potent upper disturbance moves through southern Manitoba. This disturbance may trigger some thunderstorms early on Monday morning, some of which could impact Winnipeg and the Red River Valley. Once the disturbance moves through, skies should clear, likely at some point in the afternoon. Temperatures will be in the mid to upper twenties with the wind becoming westerly due to the passage of this system.

Tuesday

Tuesday will be a nice day, as temperatures climb into the upper twenties under mainly sunny skies. Winds will be relatively light and from the south. No precipitation is expected on Tuesday, although some storms may develop overnight into Wednesday.

Wednesday

Like Monday, we may see some morning thunderstorms on Wednesday. A strong push of moisture from the south may help to trigger these storms. Should storms develop, they could be severe, but this forecast is still a few days away, so it could change. Besides the risk of storms, Wednesday will be hot and humid, with temperatures near 30C and breezy south winds.

Long Range

The long range forecast shows us cooling down after this week. Once a strong system passes through on Thursday temperatures will drop down to more seasonal values near 20C. Enjoy this little blast of heat while it lasts, it could be one of our last warm spells this year!

A Weather Moment

Tag: Thunderstorms