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! ↩

Change Is Coming

Brad Leave a comment

This week will start out with more of the same normalish weather we’ve had for the past week or so…but it looks like a change in the pattern is coming…

A cold front will swing through Manitoba on Wednesday

A strong cold front (blue line) will swing through Manitoba on Wednesday ushering in cooler weather

Temperatures on Monday and Tuesday are expected to be around normal (or slightly below), with highs in the low to mid twenties expected. Our normal high for this time of year is 25C. We will be under a surface ridge of high pressure during this time period so rain appears unlikely.

A change in our weather is in store around midweek. It appears that a major cold front will swing through Southern Manitoba at some point on Wednsday. Models disagree with the timing of the cold front, but it looks most probably that the front will enter Western Manitoba sometime early Wednesday morning and be out of the province by Wednesday afternoon or evening. Regardless of the exact timing it looks like Wednesday will be a chillier day, with highs struggling to reach 20C and rain being likely. As we move closer to Wednesday the details of the frontal passage should be better known.

After the cold front passes through on Wednesday we’ll be in for a couple of cooler days with temperatures only in the upper teens or lower twenties for Thursday and Friday. Beyond this work-week there is some uncertainty in terms of what will happen next. Many models portray us sticking with more normal weather through the remainder of August, while others show us warming up again. As always, time will tell which forecast is correct!

Elsewhere in Weather News: August 11th, 2012

Matthieu Leave a comment

Barrage of Typhoons Continue to Impact Asia

Haikui, the third typhoon to hit China this month, made landfall on Wednesday affecting over 100,000 people on China’s east coast. Rain, rain and more rain is what the region has experienced these past few weeks as typhoons Saola, Damray and Vincente (reported in previous EIWN posts) have all made landfall. On top of the severe rains brought on by these recent typhoons, Haikui has dumped an additional 200mm in areas where the grounds were already extremely saturated – inland flooding now adding another element of concern for residents.

Haikui track

Haikui’s track as it made landfall on China’s east coast. Forecasted track was as of Wednesday August 8th. (Source: TSR)

Thanks to China’s meteorological authorities who issued a red code warning (most severe) for the city of Shanghai well ahead of the typhoon hitting, many lives were saved as residents had time to vacate the premises. Authorities helped relocate over a million and a half people, mostly from the Shanghai region, before Haikui made landfall, further lessening the risk of casualties in the areas prone to flooding and landslides. Storm surge was also a concern for townships along China’s east coast.

Haikui

Satellite picture of Haikui as it made landfall just south of Shanghai. (Source: Earthweek)

In all, about one million acres of cropland and over six million of China’s residents have been impacted by this major typhoon. Flood damage has been extensive, ranging from roads washed out and stranding tourists and local residents, to homes being washed away by the flash floods. Estimated damage costs from this most recent typhoon are pegged at around the 1.5 billion dollars.

Haikui damage

One of many washed out roads caused by flash flooding in the Zhejiang Province. (Source: Global Times)

Six casualties have been associated with typhoon Haiku to date, however the death toll from the barrage of typhoons since the beginning of July, combined with heavy rains affecting the region, has brought the toll to over 100 people.

An Unsettled Sunday, Otherwise Pleasant

Brad Leave a comment

Fairly pleasant weather will be on tap for next couple days until an upper trough swings through the area on Sunday, bringing a risk of showers or thunderstorms to the Red River Valley.

Pleasant Weather Ahead

Pleasant weather is on tap for Winnipeg.

Through the next couple days, mainly sunny skies and warm temperatures will be the dominant weather across the Red River Valley. High temperatures today and tomorrow will climb up to around 29°C, while sunny skies dominate today and we move into more of a mix of sun and cloud tomorrow.

On Sunday, an upper trough begins to work it’s way into Southern Manitoba. It’s very difficult to say what exactly is going to happen with this system as it moves through. It seems clear that there will be two main areas of precipitation:

  1. An area of rain that moves through the Interlake.
  2. An area of showers and/or thunderstorms that develops over North Dakota and slides southeastwards.

As for what happens over the Red River Valley; it’s tough to say. Guidance currently suggests that there’s a moderate chance of rain for us. Should we see precipitation, it’s likely that we’d see a batch of morning showers then a little bit of sunshine before some afternoon convection bubbles up over the Red River Valley. There would be a risk of non-severe thunderstorms if that scenario happens. This system seems to be quite sensitive, so we’ll be sure to post updates in the comments below. The daytime high on Sunday will end up being somewhere between 24°C to 27°C depending on how much sun or rain we see.

Sunny skies return to start next week before another system brings a chance of rain mid-week.