Tag: Frost

Cool Weekend on Tap

Brad Leave a comment

Just when it felt like Winnipeg was out of the woods and summer had arrived, conditions will make it feel like the clock has been turned back to the beginning of the month with temperatures 10°C below normal and a risk of frost returning for the weekend. The cooler weather is courtesy an Arctic airmass that is plunging southwards behind yesterday’s potent system that brought rain & thunderstorms to Saskatchewan & Manitoba.

Today will be a very cool day with brisk northerly winds at 30km/h with some gusts up to around 50km/h.  Today’s high will top out at just 11–12°C through the Red River Valley with mixed-to-cloudy skies until the afternoon when things begin to clear up.  Winds will ease tonight with temperatures plummeting towards the freezing mark. Winnipeg will just be ahead of the main ridge axis, making sub-freezing temperatures quite possible. Areas near the core of the city may escape frost, however anywhere closer to outskirts of the city will have a strong chance of seeing some frost. The low will vary depending where in the city the temperature is measured, but in general I expect it to be around 0°C with temperatures possible 1–2°C colder than than near the outskirts of the city. Rural areas will likely deal with overnight lows of –1 or –2°C.

The remainder of the weekend looks much calmer but still cool. Saturday and Sunday will see high temperatures returning back towards the mid-teens with mainly sunny skies. Some cloud will push through late Saturday through early Sunday which should help keep the overnight lows in the low-to-mid single digits.

A Glance At Next Week

The start of next week will bring a return to more seasonable high temperatures in the 20’s, however alongside the warmer weather comes the potential for more unsettled weather as multiple systems track through the Southern Prairies & Northern Plains.

As such, Southern Manitoba will likely be dealing with a decent chance for showers or rain through the first half of the week. Depending on how things develop, rainfall totals could be anywhere from a trace to over an inch, so we’ll be sure to track things as the weekend progresses. The weather looks to settle down for the second half of the week with daytime highs in the upper teens to lower 20’s.

Coldest Weather of the Week Still Ahead

Brad Leave a comment

Unfortunately, this week’s plunge into terrible cold for September is far from over, with cooler temperatures still set to work their way into Southern Manitoba. The growing season will be at risk for a tragically early end with frost a slight possibility over the next couple nights here in the Red River Valley.

Calgary, AB and its surrounding areas have been hit particularly hard by this early-Fall oubreak of cold weather, with up to 25cm of snow causing all sorts of problems, including broken tree branches as shown in this picture taken in NW Calgary. Credit: @jpaint (Twitter)
Calgary, AB and its surrounding areas have been hit particularly hard by this early-Fall outbreak of cold weather, with up to 25cm of snow causing all sorts of problems, including broken tree branches as shown in this picture taken in NW Calgary. Credit: @jpaint

The weather story for the Red River Valley over the next few days is dominated by a rather significant high pressure system slumping southwards through Alberta. The 1034mb or stronger high is a result of a large outbreak of cold air from the high Arctic and while the high center is sliding down the foothills of Alberta, the system covers the entire Prairies.

This means that substantially below-normal temperatures[1] accompanied by brisk northerly winds will persist for much of the rest of the week before slightly milder air finally pushes across the Prairies as the high pushes southwards into the United States.

Wednesday
12°C / 2°C
Mixed skies; drizzle possible overnight.

Thursday
12°C / 1°C
Mixed skies

Friday
13°C / 5°C
A few clouds

Today will be a windy day with moderate northerly winds to around 30km/h and a high of only 12°C or so. Skies will be fairly mixed, although it will become more consistently cloudy this evening as cooler air begins working into Southern Manitoba aloft and the lakes begin producing more cloud. By late-evening a slight chance of drizzle will work its way into Winnipeg as north/northeasterly winds bring in cloud streamers off the south basin of Lake Winnipeg. Drizzle or showery weather is more likely near the Portage La Prairie region where Lake Manitoba, under slightly colder air and more favourable wind profiles undergoes more vigorous lake-effect activity.

Temperatures will drop to around 2°C or so, however it’s possible that the temperature drops to the freezing mark with some frost in some of the rural areas in the Red River Valley, depending on where cloud vs. clear skies set up.

Thursday will bring mixed skies again, although the winds should be a bit lighter than today. The high will once again be around 12°C. There will be more cloud from the lakes on Thursday night and a slight chance for some drizzle down-wind of the lakes as we head to a low of around 1°C. Once again, it’s possible some areas see the temperature drop to the freezing mark in rural regions, depending on cloud cover.

Friday will bring a shift in the weather as the high finally slumps to our south and westerly winds work their way in. We won’t see the temperature move much during the day thanks to the fact that, despite the shift in wind, southern Manitoba will still be under the influence of outflow winds from the high. The westerly winds should clear things out, allowing for our sunniest day of the week.

A disturbance will then begin diving southwards from the Northern Prairies on Friday night, spreading cloud ahead of it and slightly milder temperatures aloft. As a result, temperatures will likely be a little warmer on Friday night with lows near 5°C.

Improving Conditions for Next Week

Looking ahead, things look to begin gradually improving on the weekend. Saturday will bring some sun and cloud alongside a slight chance for some shower activity as a weak disturbance trundles through. On the backside of the system lake-effect showers/drizzle will again be possible on Saturday night. Temperatures will likely be limited to the low teens on Saturday.

Sunday will be a nicer day. At this point it looks like it will likely be a mainly sunny day with a high in the mid-teens. There’s some discrepancy in models right now with some models suggesting a mainly cloudy day, others mainly sunny. We’ll have to wait and see what exactly pans out for the day.

The NAEFS 8-14 day temperature anomaly forecast is calling for above-normal temperatures in Southern Manitoba.
The NAEFS 8–14 day temperature anomaly forecast is calling for above-normal temperatures in Southern Manitoba.

Into next week, it looks like we’ll see a return to summer weather as a surge of warm air spills eastwards across the Prairies. The NAEFS[2] is calling for above-normal temperatures in the 8–14 day outlook, which will be a welcome relief after this very early cold snap. Models are suggesting that next week will be relatively dry, with the potential for rainfall near the end of the week.

  1. Normal temperatures for around August 10th in Winnipeg are highs of 19°C and lows of 7°C.  ↩
  2. North American Ensemble Forecast System  ↩

A Cool Weekend Ahead

Brad Leave a comment

A cooler weekend lies ahead for Southern Manitoba as cooler air pushes southwards through the Prairies behind a strengthening low pressure system in Northern Ontario. Some of our coolest temperatures of the fall lie ahead although it does seem like warmer air will begin to nudge back in by the end of the weekend.

Today

Friday

14°C / 2°C
Mainly cloudy. Lake-effect showers or drizzle has a chance of moving into Winnipeg.

Today will be the most “active” weather-wise thanks to a surge of cold air at 850mb that will be diving southwards through the day today. As this air pushes over the lakes it seems quite likely that lake-effect showers or drizzle will develop and push inland in the lee of the lakes. It’s very difficult to attribute a chance of precipitation to these features as they will almost certainly form, but they produce narrow ribbons (often ≤ 50km wide) that extend along great lengths.

What are the ingredients for Lake-Effect Precipitation?

There are a few ingredients that work together to produce lake-effect precipitation. The basic ingredients are:

  • At least a 13°C temperature difference between the water surface and 850mb
  • At least 100km of fetch (the wind must travel at least 100km over the water surface).
  • Less than 60° of directional shear between the surface and 700mb; less than 40kt of speed shear between the surface and 700mb.

Which areas see precipitation will be extremely sensitive to the wind direction. Here in Winnipeg it seems that the wind will be a little too northerly for the lake effect precipitation from Lake Manitoba to move into the city, but should the winds have a slightly more westerly component we may see some light shower or drizzle activity move in. That being said, some areas in the lee of Lake Manitoba and Lake Winnipeg will likely see some showers or drizzle today. The temperature will struggle to a mere 13 or 14°C and we’ll see temperatures dip to around 2°C tonight. While there should be widespread clearing, some stratus cloud may still be advecting off the lakes. Areas that remain in cloud through the night may end up a couple degrees warmer.

Frost will certainly be a possibility through the Red River Valley tonight as skies clear and winds let up.

Saturday & Sunday

Saturday

16°C / 5°C
Sunny.
Sunday

21°C / 13°C
Sunny. Windy out of the south.

We’ll see a pleasant but cool day on Saturday with mainly sunny skies, light winds and a high near 21°C. Saturday night will bring clear skies and a low of around 4–5°C. Sunday will also be a mainly sunny day although winds will begin to pick up out of the south through the day as a low pressure system pushes towards the province. With cool air in the valley and warmer air struggling to push eastwards, it could actually become quite breezy. At this point it looks like winds will be around 30km/h with gusts to around 50, but if the cold air is a little more stubborn it could end up windier than that and closer to 40–50km/h.

Next week looks to start off with a disturbance pushing through on Monday or Monday night bringing a chance of some rain to the Red River Valley, but at this point it’s far to early to make any real judgements on what it will do. The rest of the week looks fairly quiet with seasonal temperatures.

Warm Weather Gives Way to Cool Weekend

Brad Leave a comment

Well above-seasonal temperatures will wash over Southern Manitoba today as a powerful low pressure system in the Arctic drags a swath of very warm air eastwards across the Prairies. It won’t be meant to last, though, as a strong ridge of high pressure builds in behind a cold front that pushes through on Saturday, bringing cool Arctic air with it for the weekend.

Friday

25°C / 15°C
Mainly sunny.
Saturday

22°C / 4°C
Cloudy with a good chance of showers or thundershowers, then clearing through the afternoon.
Sunday

19°C / 6°C
Mainly sunny and cool.

We’ll see a breezy wind out of the southwest today as temperatures climb into the mid–20’s thanks to a warm front that pushed through overnight. We might see a little bit of cloud, but for the most part skies should be mainly sunny. Still in the warm sector of this system, we’ll only drop to the mid-teens tonight with some increasing cloudiness towards Saturday morning as the cold front approaches.

Saturday morning will bring a fairly decent chance for some scattered shower activity as the cold front pushes into the Red River Valley from the north. There may be a few thundershowers as well but no significant or widespread thunderstorm activity is expected. Gusty northerly winds will move in behind the cold front – which should be through much of the Red River Valley by midday – with clouds scattering out to a mix or partly cloudy skies. The temperature should be able to climb a degree or two above the 20°C mark, however cold air advection will limit our high very close to that mark.

Skies will clear overnight as we drop down to a very chilly 4°C or so. Areas outside the city of Winnipeg may even see temperatures dip a little cooler than that. We may end up seeing the first frost of the year in some places on Saturday night but I don’t expect a widespread frost to occur.

Sunday will be a sunny but very cool day as the ridge of high pressure dominates the weather pattern over Southern Manitoba. We’ll see temperatures climb to only around 17 or 18°C by late afternoon but at least the winds should be relatively light, picking up out of the south later in the day to only around 15–20km/h. We’ll see an overnight low of around 7°C on Sunday night with clear skies.