Tag: Lake-Effect Showers

Last Day of Summer Will Be Cold, Wet and Windy

Brad Leave a comment

Far from the sunny skies and warm temperatures we’ve seen constantly over the last several months, today will be cold, wet and windy as a cold front blasts through the Red River Valley.

GEM-REG 850mb Temperatures

850mb temperatures from the GEM-REG model valid for this evening. A significant outbreak of cold air will occur over Southern Manitoba today.

A powerful cold front will push southwards through the Red River Valley today, beginning in areas north of Winnipeg early this morning, then pushing through Winnipeg mid-to-late morning and then pushing through the rest of the valley and southeast Manitoba by early this afternoon. There will be an area of showers that pushes through the central and eastern Red River Valley, with rain further east in the Whiteshell along and behind the cold front. Generally speaking, if you’ve seen showers in the past two days, you’ll likely see more today. Winnipeg will likely only see 1-2mm, however anywhere from 2-10mm are possible in the eastern Red River Valley to the Ontario border. In addition to the precipitation, strong winds will once again develop over the Red River Valley, with winds increasing out of the north to 40-50km/h with gusts to 60-70km/h immediately behind the cold front.

This system will be dragging the coldest temperatures aloft that we’ve seen this month; 850mb temperatures will drop to anywhere from -5 to -8°C. This will result in fairly significant low-to-mid-level instability, mainly through the Interlake and arcing southeastwards across the South Basin towards Sprague. This will have two main impacts:

  1. Today, associated with the passage of the cold front, there’s a chance for an isolated thundershower through the Central/Southern Interlake and the Dugald/Beausejour/Grand Beach region. They will not be very strong, however they may be able to produce small hail.
  2. As the winds at various heights in the atmosphere slowly line up, lake-effect streamers will develop this evening and overnight off of Lake Winnipeg. The location of the precipitation will be sensitive to the exact wind direction, however, in general, the regions that will be effected the most will be up in the Arborg area (from the North Basin), and then further south in the Dugald/Beausejour/Grand Beach region (from the South Basin). There will also likely be streamers in the Portage la Prairie region overnight from Lake Manitoba, however they’ll be weaker as a surface ridge approaches from the west overnight. There will only be a slight chance of isolated showers in the southern half of the Red River Valley overnight. Winnipeg will be nestled between the two bands of streamers to our west and east, however there’s a distinct chance that we could see the streamer from the South Basin move into the city overnight.

In addition to the streamers, the other significant weather tonight will be frost. Areas that clear out tonight, which will be most areas that aren’t in the lee of the lakes, will see frost with overnight lows in the -1 to -3°C range. There’s a chance that areas in SW Manitoba may see overnight lows dip as low as -5°C underneath the surface ridge.

For Saturday, here in the valley we’ll see clouds & showers from the lakes last until midday before things start to clear up in the afternoon. Temperatures will remain cool with highs only around 11°C. We’ll likely see a hard freeze tomorrow night with overnight lows in the -3 to -5°C range across most of Southern Manitoba.

On Sunday, we’ll finally see some warmer air make it’s way towards us. The models want to push temperatures as high as 18-19°C through the Red River Valley, however we often see cold air stick around a little longer than forecast. Winds are forecast to shift to the southwest, however it’s almost certain that if they don’t quite make it to SW and end up being southerly we’ll see daytime highs a few degrees cooler than that. We should see temperatures in the mid-to-upper teens last through much of next week with little significant weather on tap.

Frosty to Start the Week

Brad Leave a comment

We’ll be in for a couple of chilly, perhaps you could even say frosty, days to start this week. Cool daytime highs and sub-zero nighttime lows are on tap.

GEM-REG 3hr. Precipitation Accumulation

Some light lake effect showers (shown in blue) are expected to develop on Monday as cold air flows over the relatively warm lakes winnipeg and manitoba.

After a rather chilly Monday morning, temperatures won’t make a dramatic recovery for the afternoon. Daytime highs on the first day of the week are expected to barely make the double digits in most areas, with highs generally in the 9-12C range expected. A breezy north wind and perhaps a couple of lake-effect showers won’t make the day any more pleasant. Tuesday night should be another cool one in Southern Manitoba. However, it appears frost will be isolated to areas around and east of the Red River Valley as some warmer air moving in from the west will keep temperatures above zero overnight in Western Manitoba. Daytime highs on Tuesday will be an improvement from Monday, though except for South-Western Manitoba where 20C values are expected, temperatures will generally remain stuck in the mid teens.

Yet another cold front will swing through overnight Tuesday into Wednesday ushering in another cool airmass to end the week. It appears high temperatures will be relegated to the teens from Wednesday through Friday. There appears to be slim odds of any significant precipitation this week, though we may at least get some measureable rain later in the week as a few strong impulses rotate through the region.

NAEFS Ensemble 8-14 day outlook

The NAEFS ensemble doesn’t give a strong indication of what type of weather we’ll see moving forward…

At this point the long range forecast looks fairly status quo. We’ll see some cooler than normal days and some warmer than normal days, but in general the pattern for the next week or two generally looks to be near normal on average. However, there will certainly be a fall feel to the air as nighttime temperatures regular drop down to the freezing mark and daytime highs stay close to the average high for mid-September of 18C.

Streamers This Morning; Seasonal Weekend

Brad Leave a comment

After lake-effect streamers diminish this morning, we’ll see mainly sunny skies for the rest of the weekend with daytime highs near or just above 20°C.

GFS 500mb Wind Speeds

500mb wind speeds from the GFS model valid mid-day today. Faster winds are shaded. This clearly depicts how Winnipeg is in between the cooler air of the upper low, situated over James Bay, and the warmer air of the upper ridge/high, situated over the Western Prairies.

We’ll see clouds this morning with some showers over the Northern Red River Valley. These showers will be lake-effect streamers, so they’ll impact fairly long, narrow areas downwind of the lakes; where exactly will see showers will be highly dependent on the exact wind direction, so checking out where they are using our RADAR Viewer is your most reliable way to see if you’ll be impacted by them. Winnipeg will likely escape mostly unscathed from the streamers this morning, although should the wind shift to be a little more northerly (more favourable) or westerly (less favourable) we certainly could see some precipitation.

A ridge will slowly start building eastwards across the Prairies today which will bring a more westerly component into our winds across the province this afternoon and help start clearing out the clouds. By mid-to-late afternoon we should see sunny skies with a high right around 20°C here in Winnipeg. Tonight we’ll see clear skies with an overnight low dipping down to about 10°C.

Saturday will bring sunny skies and a high near 21°C as the ridge continues to try and build eastwards. A weak disturbance sliding SE across Manitoba will, however, pull some cooler air southwards across the province which will cause us to have our coolest overnight lows in quite a while across the Red River Valley. Here in Winnipeg, it looks like the overnight low will dip to 6 or 7°C in outlying areas, with temperatures a couple degrees higher near the core of the city.

Warmer air finally is able to push in on Sunday, which will give us a high near 24°C under sunny skies.

The beginning of next week looks to be sunny with slightly above-normal daytime highs.

Cool Blast Across Manitoba

Brad Leave a comment

A powerful low pressure system moving through the Interlake will bring significantly cooler weather to Manitoba over the next couple days. Read on to find out where the rain will be and how cool it’s going to get.

GFS Forecast for this evening

GFS 850*mb* temperature forecast for this evening. I’ve drawn on the strong high over the Western Prairies that is helping our low pressure system pull down cool Arctic air. Cold front and warm fronts have been drawn in blue and red, respectively.

As the low pressure system passes to our north today, it will drag a cold front through the Red River Valley over the course of the afternoon. Preceding this front will be an area of rain, and while a majority of the thunderstorm activity will be through the Interlake, closer to the low, there will likely be some isolated embedded thunderstorms through the Red River Valley.

Accumulations will generally be higher the further north from the international border you go; while up to 25-50mm will likely fall through the Interlake, only 2-5mm are expected over the southern RRV. Any location in the RRV that sees a thunderstorm could easily receive between 0.5 to 1” of rain. Here in Winnipeg, we’ll probably see between 5-10mm with some locally higher amounts if a thunderstorm rolls through by the end of the day.

On the backside of this system a strong northerly wind at all levels will drag down the most potent shot of cool, Arctic air we’ve seen in quite a while. While winds will be out of the south in the morning, gusty northerly winds will kick in quickly behind the cold front, with sustained speeds between 40-50km/h and gusts as high as 60-70km/h. 850mb temperatures approaching 0°C will push down into the Interlake region tonight. This will bring with it the chance for the first significant lake-effect shower event of the “fall”1 season. When looking for the generation of lake-effect showers, there’s a few things to look for:

  1. A temperature difference from the surface to 850mb of at least 13°C.
  2. Less than 60° of wind shear between the boundary layer and 700mb; preferably less than 30°.
  3. At least 100km of fetch which the air travels over open water.

Given that lake temperatures are still sitting at 22-24°C, we’ll certainly see plenty of clouds develop and move south off the lakes. Whether or not lake-effect showers develop will depend precisely on the winds, but it looks fairly favourable right now with winds forecast to be from the NW with minimal directional shear. We’ll likely see some streamers develop overnight, providing showers or drizzle to communities in lee of the lakes. Current forecasts put these narrow bands of precipitation between Portage & Winnipeg and just east of Winnipeg, but we’ll have to see what the actual wind direction ends up being as to where they’ll go. Right now it looks like there won’t be enough of a westerly component to the wind to bring them into Winnipeg.

If the surface winds end up too westerly, or the 850mb temperatures don’t cool off quite as much as forecast, then no streamers will form. It will be interesting to see what happens!

In the end, it could certainly be worse than it’s going to be. The coldest air will be over us during the overnight period, and we’ll likely have cloud cover as well which will help keep things a little warmer. By the time Thursday afternoon rolls around, the cold air will already be exiting the region, so we won’t end up dealing with temperatures quite as cool as many other areas across the Prairies will.

  1. It’s not fall yet! ↩