As things become clearer regarding the impending Colorado low set to impact Southern Manitoba Tuesday night through much of the remainder of the week, Environment Canada has issued a Special Weather Statement for the entire region.
"Ahead of a Colorado low, some light snow and freezing drizzle will occur over southern Manitoba Monday night into Tuesday morning," noted the Statement. "The Colorado low will move through the upper Midwest of the United States bringing snow into the region starting Tuesday night and into Wednesday. With the above seasonable temperatures in place as the low pressure system approaches, the snow is expected to be a heavier wet snow."
As the area of low pressure moves through the Midwestern states toward the Great Lakes on Wednesday night and into Thursday, a hang back area of snowfall is expected to linger over southeastern Saskatchewan and southern Manitoba through the week.
According to Environment Canada, the worst conditions are expected to be in the communities along the international border. The accumulations will in general range from 10-20 cm, with some local amounts reaching as high as 30 cm by the weekend.
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At this time, it appears that for each forecast period, snowfall amounts are expected to stay sub-warning. However, with the snow beginning overnight on Tuesday, and continuing to snow through the week, the accumulation of snow over such a prolonged time will have continuous impact over the region. Snowfall Warnings are issued in Manitoba and Saskatchewan when When 10 cm or more of snow falls within 12 hours or less.
As this area of precipitation lingers, some regions in eastern Saskatchewan and western Manitoba may see higher snowfall amounts as the system interacts with the higher terrain in the region.
Conditions will improve Friday into Saturday as the Colorado low continues to track eastward, ushering in another surge of Arctic air, bringing back more normal temperatures.
For our initial story published Monday morning with CMOS Accredited Weathercaster Chris Sumner, please see below.
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It may be taking a little longer than initially expected, but a massive Colorado low is still on track to impact much of Southern Manitoba beginning Tuesday evening and lasting, potentially, into Thursday morning.
"The timeline has been pushed back about 24-hours from our initial forecast heading into the weekend, but the impacts expected are essentially still the same," said CMOS Accredited Weathercast Chris Sumner Monday morning. "Cloud cover will thicken throughout the day Tuesday, giving way to flurries late in the afternoon, before snow starts tomorrow night and continuing into Wednesday. Throughout this event, we can expect waves of snowfall, so there more than likely will be breaks in the snow from time to time, but again I want to stress, this will be a significant snowfall event for our region."
This system will develop quickly Monday, and move eastward through the U.S. plains, before essentially stalling to just more than a crawl due to blocking high pressure centred over Hudson Bay and northern Quebec.
"That part of the forecast hasn't really changed," he said. "That blocking high is why this system will basically sit over the Dakotas and northern U.S. plains for 48-hours plus. As it very slowly creeps along, it will continue to tap into moisture rich air from the Gulf of Mexico and cold air to the north of it, meaning ample potential for substantial snowfall."
Based on current guidance, Sumner is expecting the heaviest snow to come overnight Tuesday through Wednesday morning, before backing off somewhat during the day Wednesday.
"Snowfall rates may decrease by the time we get to Wednesday afternoon, but the snow will continue into the evening and overnight hours to Thursday morning," explained Sumner. "Even though, at this point, we're expecting the bulk of the snow to fall from Tuesday night to Wednesday noon, it's highly likely we still see another few centimeters during the latter half of the event into Thursday."
And just how much snow can we expect?
"All signs continue to point toward a general 10 to 15cms for all regions south of the Trans Canada highway, with 20cms or more very much on the table," he added." This will be heavy, wet snow and the bottom line is, we can expect a lot of it."
Northeasterly winds Tuesday night and Wednesday will mean some blowing and drifting snow, but at this point it’s looking like those winds will be breezy, but not gusty. Sustained winds of 30 to 40 km/h can be expected, but as this massive storm pulls eastward, northerlies will pick up to 40 to 50 km/h Thursday afternoon through Friday, meaning blowing and drifting snow could be a concern well after the main area of the low has moved away from the region.
Temperatures over the next few days will remain above average, with highs between -1 and +1 Monday through Thursday. Averages for this point in December are -9 daytime and -18 overnight.
"Once this Colorado low finally gets a move on, in behind it a trough will develop in the jet stream, and that means cold, Arctic air will descend over the area," said Sumner. "Much cooler conditions are expected for the weekend, and early next week, as we see highs sink to the -14 to -17 range as soon as Saturday."