Tag: Inverted Trough

Will Our First Snowfall of the Year Come This Week?

Scott Leave a comment

Will our first snowfall of the year come this week? That is the question that meteorologists are trying to answer as a complex weather system potentially brings accumulating snowfall to southern Manitoba tonight.

An inverted trough pattern associated with a strong system to our south may help bring snowfall to southern Manitoba
An inverted trough pattern associated with a strong system to our south may help bring snowfall to southern Manitoba

This Week

Today will start out cloudy and cool with temperatures hovering near the freezing mark. Change is coming, however, as a strong weather system moves off the mountains and begins to produce snow over the northern United States and southern Prairies. This is a complex system, with the strongest part well to our south over the midwestern US. A secondary part of this system will move across the southern Prairies and likely produce accumulating snowfall along part of its track. At this point it appears probable that snow will begin to develop over southern Manitoba on Monday night as moisture and lift begins to push into the region. The question is whether conditions will come together just right to produce significant snow over all of southern Manitoba, or whether the system will only begin to produce significant snow as it pushes into northwestern Ontario.

Weather model simulations generally begin to produce light snow over western Manitoba late on Monday afternoon, before the snowfall intensifies as it moves into the Red River Valley and southeastern Manitoba. This would likely result in 1-4 cm of snow over western Manitoba, 4-8 cm over the Red River Valley, and 5-10 cm over southeastern Manitoba. However, an alternative solution would have only minor snowfall (if any) over western Manitoba and the Red River Valley, with slight accumulations of 2-4 cm over southeastern Manitoba. The former solution is most favoured at this time, with about 5 cm expected in the Winnipeg region, with slightly higher amounts to the east and slightly lower amounts to the west. The most likely outcome may change as the system develops today, therefore you should stay tuned for more details.

A map of the currently favoured snowfall outcome is shown below, showing the probability of at least 5 cm of snow; note that Winnipeg has a 70% chance of receiving at least 5 cm. Some blowing snow is possible, due to southeasterly winds of 30 km/h gusting to 50 km/h today, however blizzard conditions are definitely not expected. Winds will taper off by Tuesday, alleviating any blowing snow that does develop. The first major snowfall of the year is always one of the most challenging as drivers adapt to the changing conditions. Regardless of whether it snows tonight, this is probably a sign that you should get those winter tires on if you haven’t already!

Probability of at least 5 cm of snow according to the NAEFS (ensemble)
Probability of at least 5 cm of snow according to the NAEFS (ensemble)

Snow will taper off on Tuesday morning, should it materialize in the first place, leaving Tuesday with cloudy and cool conditions. Temperatures will once again sit near the freezing mark under mainly cloudy skies. The odd flurry is possible during the day, but generally quiet weather is expected. Winds will be light from the west.

A quiet weather day is expected on Wednesday as well, with mainly cloudy skies and just a lingering chance of flurries. Temperatures are likely to be around or just above zero. Winds will be northwesterly at 20-30 km/h.

Long Range

The long range outlook will be partly shaped by how much snow falls this week. If we manage to avoid major snow, it is likely that the remainder of November will remain generally warmer than normal. Because a blanket of snow on the ground reflects most of the incoming sunlight, it is more difficult for us to heat up during the day. The longer we avoid snow the longer we’re able to keep that darker, exposed soil which helps to absorb the limited sunlight that we do receive at this time of year. Should we receive significant snow with this upcoming system, we’ll likely see normal conditions through month’s end. Regardless of how much snow falls this week, this November is likely to end up as one of the warmest, if not the warmest, Novembers on record in Winnipeg.

A Cold Weekend To Close Out With More Snow

Brad Leave a comment

The cold front that pushed through last night will usher in a reinforcing shot of Arctic air which will drop our temperatures back below-normal for the next few days. The weather will remain fairly benign until Sunday when a potent inverted trough low-pressure system will bring snow to Southern Manitoba.

Friday & Saturday

Friday
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Mostly cloudy with light scattered flurries. Clearing overnight.
-13°C / -21°C
Saturday
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Sunny.
-11°C / -21°C

We’ll see mainly cloudy skies today with some light flurries scattered through the Red River Valley. Temperatures will be quite cool with a brisk northerly wind limiting our daytime high to only –13°C as it ushers Arctic air into Southern Manitoba. Skies will slowly clear out overnight as we head to an overnight low near –21°C. On Saturday we’ll see sunny skies with light winds and a high near –11°C. Temperatures will drop back to around –21°C again Saturday night under clear skies.

Sunday

Sunday will be the most active weather day we’ve had in Southern Manitoba in a while. An inverted trough will push into Southern Manitoba through the morning hours with snow beginning over SW Manitoba through the morning and moving into the Red River Valley by the evening. Right now it looks like this system will develop in a somewhat complex manner; a low pressure system will push out of Montana and intensify as it moves into South Dakota and taps into moister air over the Central Plains. This moisture will surge northwards ahead of the low, which will be rapidly evolving as it interacts with a strengthening shortwave travelling along the MB/ND border. The low will rapidly develop a sharp inverted trough and feed plenty of moisture into it. This is not dissimilar to the setup earlier this month that brought 2 feet of snow to some communities in the SW Red River Valley, but at this point it does not look like this system will be nearly as potent.

Liquid-equivalent precipitation amounts from the GDPS from Sunday morning to Monday morning.

Liquid-equivalent precipitation amounts from the GDPS for Sunday morning through Monday morning.

At the moment, it appears that most communities near the International Border (from Melita all the way to Emerson) will see between 10–20cm of snow; regions near the western escarpment of the Red River Valley may see an additional 5–10cm above that figure due to localized upslope enhancement from the easterly/northeasterly winds that will set up with this inverted trough. Further north in communities along the Trans-Canada Highway (Brandon, Portage la Prairie, Winnipeg), snowfall accumulations will be quite a bit less. Currently it looks like around 5–10cm can be expected, diminishing to closer to 5cm in the Whiteshell. This is simply a first guess, though; this system may end up developing in a completely different manner should only a few small things change. I’ve erred on the side of caution, giving what I think is a “worst case” scenario. Snowfall amounts could very well be less than mentioned here; we’ll provide an update tomorrow in the comments below updating what this system looks like it’s doing, along with a snowfall forecast map.

Next Week

This system will push off into Ontario on Monday and we’ll begin a slow trek back towards seasonal temperatures through the rest of the week. With warmer air trying to push into the province, it looks like we’ll have several chances to see more snow with as a more unsettled pattern develops.

Another Shot of Snow on the Way

Brad Leave a comment

More snow is on the way for Southern Manitoba this weekend as a low pressure system moves across the Dakotas.

NAM Precipitation Accumulations for Saturday

NAM liquid-equivalent precipitation accumulations for Saturday afternoon/evening.

It will be a cool day across the Red River Valley today as any left over cloud moves out, allowing our temperatures to slowly drop to around -16°C by this afternoon. Temperatures will dip down to around -21°C tonight before some cloud associated with the approaching low pressure system moves in.

Snow will spread into southwest Manitoba tonight and reach the Red River Valley tomorrow morning. It will last through much of the day before tapering off in the evening. One of the main challenges with this system is it’s complex nature: the feature pushing across Southern Manitoba is known as an inverted trough. These complicated features are notorious for being difficult to forecast the snowfall intensities they’ll produce.

In general, it looks like the heaviest snowfalls will be along and south of the Trans-Canada Highway, including Winnipeg, with an average of 5-10cm. There are some hints within the model outputs that some areas may see as much as 10-15cm, however it’s a little hard to say that with confidence since there is absolutely no developed reflection of how this system is taking shape right now. The area that is most likely to potentially exceed 10cm of snowfall is in extreme SE Saskatchewan into SW Manitoba, west of the RRV and south of the TCH. At this point, it looks likely that Winnipeg will see 5-8cm of snow tomorrow.

Skies will clear across Southern Manitoba tomorrow night, bringing another cold night to the Red River Valley with overnight lows dipping to -20°C. Sunday will be mainly sunny with a high of about -15°C.