Tag: Shortwave

A Snowy Start to the Weekend

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A compact shortwave moving across southwestern Manitoba will bring snowfall to the Red River Valley and areas west today and tonight.

500mb vertical velocities for 18Z today

500mb vertical velocities for 18Z today. This image shows an area of lift (air moving upwards) over the Red River Valley by noon today. This will contribute to the generation of snowfall over the area.

A broad area of moderate lift ahead of a shortwave is producing an area of snow that will push eastwards into the Red River Valley by late morning, although the exact eastward extent of the snowfall will be quite tricky to nail down as the lift creating the snow will [somewhere near the Red River Valley] slow down and pivot to the south as the shortwave dives into the Dakotas.

Before we get to snowfall accumulations, we’ll quickly cover our temperatures for the weekend. Because no surface fronts are associated with the weather we’ll get (all of the forcing is aloft), temperatures through the Red River Valley will not vary too much from yesterday. Daytime highs through the weekend will vary from about 0°C to 2°C. Overnight lows through the weekend will generally sit around -4°C, plus or minus just a couple degrees.

Onto the snowfall! Snow has spread into SW Manitoba overnight, bringing light to moderate snow that will last another 12-18 hours. Snow will begin to push into the RRV by late morning, however the eastern extent is difficult to pin down with amounts likely diminishing somewhere over the eastern Red River Valley into the Whiteshell. One of the biggest challenges to this system will be the SLR: snow-to-liquid ratio. This is a measure of how much snow a certain amount of water will generate. Typically on the Prairies, SLRs tend to be in the 10:1 to 15:1 range; if you had a 10:1 SLR, that would mean that 1mm of liquid water would produce 1cm of snow. If it were 15:1, then 1mm of liquid water would produce 1.5cm of snow.

Over southwestern Manitoba models are predicting generally 10mm of precipitation, over the Parkland regions of Manitoba about 5-10mm is expected to fall and over the Red River Valley, 2-5mm is forecast. Best guidance is showing SLR values of around 11:1, which would result in the following snowfalls:

  • Southwestern Manitoba: 11cm
  • Parkland Manitoba: 6-11cm
  • The Red River Valley: 2-6cm

The greatest uncertainty with this system is how far eastwards the snow will push, but in general, this will be the first accumulating snowfall in quite a while over Southern Manitoba. Winds will be light throughout this event, which will prevent blowing snow from being a problem, but drivers should be prepared for the potential of poor driving conditions through the Red River Valley and areas across the west and southwest portions of the province tonight through tomorrow morning.

Some lingering light snow will be out and about through the rest of the weekend, but no significant snowfall is expected.

Hot, Sunny Weather This Week

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Winnipeg and the Red River Valley will be basking in hot, sunny weather this week as an upper ridge pushes it’s way across the Prairies. We’ll see a chance of thunderstorms on Thursday evening as a disturbance rolls through the RRV, but quickly return to sunny, warmer-than-seasonal weather.

850mb Temperatures this evening from the GEM-REG

850mb temperatures for this evening from the GEM-REG model. Warm air is building into S. MB bringing daytime highs near 30°C.

A broad southerly flow ahead of an incoming upper ridge has pumped temperatures up over Southern Manitoba back to the 30°C mark. 850mb temperatures will climb up to nearly 20°C today, which will allow our daytime high to soar towards 31 or 32°C. The warm air in place over us will also result in a dramatically warmer overnight low; while the past couple nights have dropped into the low-to-mid teens, we’ll see the mercury barely dip below 20°C tonight.

The normal daytime high for late August in Winnipeg is about 24°C. The normal overnight low is about 11°C.

Thursday will be another warm day, however an incoming shortwave will slide along the International Border through the day, bringing some showers on Thursday morning to SW MB and the risk of an isolated thunderstorm to the Red River Valley, from the Winnipeg area all the way south to Fargo. If storms develop, they’ll develop late in the afternoon along a weak trough line that’s expected to develop in response to the upper feature. Ultimately, I think that most of the storms will remain south of the border with only a very slight chance of anything popping up on the Manitoba side of the RRV. Scott’s Southern Manitoba Mesonet will be a great way to track the trough through the afternoon to see if the threat for storms has passed by you. Despite the heat that will be present with daytime highs near 30°C, dynamics look fairly weak and I do not expect that any storms that may develop will become severe.

We’ll see temperatures dip to around 15°C on Thursday night. On Friday, we’ll see plenty of sun and daytime highs continuing to be near 30°C.

For the weekend, it looks like a cold front will sweep into the province on Saturday, bringing with it some showers and cooler weather; daytime highs look to be in the low-20’s for Saturday. Temperatures look to rebound quickly on Sunday, though, with highs pushing back to the high-20’s. So despite our rather cool start to the month, we may yet come out with our 14th consecutive month of above-normal temperatures in Winnipeg. 5 days out of the next 7 are forecast to have daytime highs at least 3°C above normal, and overnight lows look to remain above normal as well.

Surprise! More Hot Weather

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This week will be another hot one in Southern Manitoba and indeed all over Western Canada. The potential for thunderstorms during the week may temper the heat somewhat.

A large ridge of high pressure will reside over Western Canada this week

A large ridge of high pressure will reside over Western Canada this week

The weather forecast for this week will be rather tricky. What we do know for sure is that it will be hot all week, with high temperatures being near 30C every day. However, what is somewhat unclear is the risk of thunderstorms during the week. Let’s start with the easy part – the heat.

Temperatures will start out the week in the upper twenties or near thirty on Monday and Tuesday in Southern Manitoba. Humidity levels should remain low on these day making conditions hot, but not excessively so. By Wednesday high temperatures should be be in the low thirties with the humidity making it feel closer to 40. It currently appears that temperatures for late week will remain around the 30C mark, with humidity levels remaining elevated.

A shortwave will move toward the Eastern Prairies on Wednesday, potentially helping to trigger thunderstorms

A shortwave will move toward the Eastern Prairies on Wednesday, potentially helping to trigger thunderstorms

The presence of heat and humidity over the Prairies this week will cause the atmosphere to become unstable, creating the risk of thunderstorms on many days. Unfortunately, the thunderstorm forecast is not entirely certain. The issue is that a large region of high pressure, such as the one we’ll be under, does not typically promote widespread thunderstorm activity. In fact high pressure usually suppresses convective activity. It looks like this ridge will not be very good at suppressing thunderstorms, which complicates the forecast significantly.

At this point it looks most likely that Southern Manitoba will see thunderstorms mainly during the second half of this week, from Wednesday onward. During that time period the atmosphere will be most unstable and there will be some weather features moving through the region which may trigger storms. The jet stream has weakened significantly over the Prairies as of late, meaning that most storms will be non-severe in nature. Heavy rain will likely still be a concern though due to slow storm motion. Some severe storms will also be possible just simply due to the instability present in the atmosphere. Although stronger storms will certainly be less widespread than weaker ones. As the week progresses we’ll have to reassess the thunderstorm risk one day at a time.

While my forecast for this week might seem a bit equivocal, that will just be the nature of the weather in the short-term. Unfortunately thunderstorms are just simply unpredictable a frustrating but unavoidable aspect of mother nature.

More Showers Than Thought?

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A few systems are expected to bring chances for showers and thunderstorms to Southern Manitoba over the next few days as the upper ridge takes a few days longer to build in than previously thought.

30-Day Rolling % of Normal Precipitation for the Canadian Prairies

30-day % of normal precipitation for the Canadian Prairies. This map depicts the increasing drought conditions over much of the Red River Valley, with most areas only seeing only about 60% of the normal amount of precipitation over the last 30 days.

Offering a slight bit of relief to the dry conditions over the Red River Valley, an area of rain blossomed in North Dakota overnight and has pushed into Southern Manitoba this morning. Amounts are generally expected to be between 5-10mm along the International Border with amounts dropping off quickly to the north. This system will push into NW Ontario by late morning and skies will clear out behind it. Under sunshine our temperatures will soar to nearly 30°C in the afternoon.

The subtropical ridge that was previously progged to push into the Southern Prairies has instead decided to stay more or less where it was for a few extra days, which will leave us with a more zonal flow through this weekend. Fortunately, this means that we’ll have more chances for precipitation than previously thought.

The next chance for rain will come on Saturday afternoon/evening as a shortwave that will move across Saskatchewan today slumps southeastwards across the Interlake and Red River Valley. A couple showers and thunderstorms are likely to fire up underneath the shortwave as it crosses the RRV in the late afternoon. Currently all the convective parameters look to be fairly middling, so I don’t expect any severe weather to occur. Saturday will have a daytime high of 28°C before clouds move in in the afternoon. The low on Saturday night will be around 15°C.

Sunday should be a sunny day with a high near 28°C.

The next chance for rain will be Monday night as a shortwave slumps down the upper ridge that will build into the Western Prairies over the weekend. After that, it looks like the ridge will continue building into the Eastern Prairies, bringing us sweltering hot temperatures ove 30°C by the end of next week.