Tag: Lake-Effect Drizzle

Cool Weekend, Warming Next Week

Brad Leave a comment

Cool weather will persist across Southern Manitoba this weekend as the region remains under the influence of an unseasonably cold outbreak of Arctic air. Temperatures will continue to slowly moderate, however things will be generally mixed through the weekend with a fair amount of cloud and slight chance of precipitation. The real warm-up will build into the region next week, returning us to summer-like weather.

Friday
13°C / 4°C
Mainly sunny

Saturday
14°C / 5°C
Mainly cloudy

Sunday
14°C / 5°C
Mixed skies

Today will be the nicest day that the area has seen in a while thanks to a westerly wind which will help dry out the low-levels and clear out the cloud that has been so persistent over the past week. Thanks to that, mainly sunny skies will be seen in Winnipeg and throughout much of the Red River Valley with westerly to southwesterly winds up to around 20km/h. Temperatures will remain cool, however, as the wind will be outflow from the colder air mass slumping to our south; highs through the Red River Valley will sit near the 13°C mark.

Tonight will see mainly clear skies with a little bit of cloud working in from the northwest late in the overnight period and a low near 4°C.

Cool, Mixed Weekend

Saturday will be a mainly cloudy day as a weak trough of low pressure swings through the Red River Valley. While no precipitation looks likely, there will be a slight chance of some isolated, light shower activity. The temperature will climb to around 14°C for a high temperature in the valley.

Skies will begin to clear overnight as the trough slides off into Ontario and winds back to northwesterly, although another slightly cool shot of air will be moving in behind the trough so some cloud with a chance of showers or drizzle in the lee of the lakes is likely. Lows will be near 4 or 5°C in Winnipeg & through the Red River Valley.

Sunday will bring mixed skies with a chance of drizzle or showers in the lee of the lakes. The high will once again be near 14 or 15°C while the overnight low drops to a repeat 5°C.

Warmer Weather Next Week

The NAEFS is forecasting above-normal temperatures across Southern Manitoba in the 8-14 day outlook.
The NAEFS is forecasting above-normal temperatures across Southern Manitoba in the 8–14 day outlook.

Manitobans will be repaid for their patience with the cold weather – if medium-to-long-range enesemble models are to be believed – with a hurried return to summer-like conditions. Both Canadian and American models show an upper-level ridge building eastwards across the Prairies next week brining significantly warmer air with it.

850mb temperatures will climb early next week from the –2°C or so they sit at this morning over Winnipeg to around 10°C. This warming aloft will translate to significantly warmer temperatures down here where we live, with daytime highs moving from low-to-mid teens up to the low 20’s.

The weather also looks fairly dry through the warm-up, although by week’s end there looks to be a chance of showers or thunderstorms as a low pressure complex tracks eastwards through the Prairies & Northern Plains of the United States.

Coldest Weather of the Week Still Ahead

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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.