Winter lovers rejoice! Snow is on the way, timing here
Monday, December 4, 2017, 8:26 AM - A mild start to December across much of southern Canada will be ideal for putting up outdoor holiday decorations, knocking out your shopping early, or cleaning up the yard. However, for many it will not look or feel like December. How long will you have to wait for more typical winter weather?
The answer depends on where in the country you call home, as an upcoming pattern change will shake up the map, bringing big changes from coast-to-coast. We have the details below on when the change will occur, and a region-by-region breakdown of what to expect as we head deeper into the month.
The change in the pattern will begin this week with a developing ridge over the Gulf of Alaska. As high pressure builds, the jet stream will deflect northward. On the downstream side of this feature, a northwesterly flow will develop, opening the door for Arctic air to spill across the continent.
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Meanwhile on the other side of North America, a similar ridge will build into the North Atlantic and Greenland. This will effectively form a block, keeping the trough locked in over North America.
With nowhere else to go, the Arctic air near the pole will be forced to dive southward, setting up several rounds of cold air outbreaks for the middle of the country and a sharp temperature contrast along the Atlantic coast, which will be a prime location for storm development.
The pattern change will start to evolve during December 4-7, and will be accompanied by a round of active weather as a Colorado Low tracks into Northern Ontario.
After the pattern gets established, here is what we expect the jet stream pattern to look like during the 2nd and 3rd weeks of December.
And here’s what that means for your forecast, region-by region:
After a stormy November, mild and dry conditions will develop along the Pacific coast for December. Rising melting levels should cut into the snowpack that was developed over the last few weeks, which will keep local rivers and streams running high. Unfortunately, this will also impact ski resorts as we head towards the holiday season. Also, while high pressure often means abundant sunshine, the sinking air along with colder air trapped in the valleys provides the set-up for localized areas of persistent fog and air quality concerns.
Above seasonal temperatures will dominate over the next couple of weeks as the Pacific influence will often win over the Arctic air. However, at times the arctic air to the east will clip Alberta, and more direct impacts are possible later in the month.
This region is expected to see cold dominate through mid-December, with multiple shots of Arctic air on tap during the period. Passing Clipper systems should bring some additional snow chances, on top of the snowpack that has already developed through the autumn.
The first round of colder weather will just bring typical mid-December temperatures to the region, but it will be cold enough for bands of lake-effect snow in the traditional snow belt areas and into Niagara as well. Several reinforcing shots of Arctic air will invade the region as we head towards mid-December. This will result in several high impact lake-effect snow events and allow ski areas to build substantial bases as we head towards the holiday season. A few clippers are likely as well which will bring more widespread snow at times to areas outside of the lake effect snow belts.
Quebec and Maritimes
Cold air will be found here as well, setting up a sharp zone of temperature contrast between the continent and the still-warm north Atlantic. This is a prime setup for storm development, meaning that a period of more active weather is likely for the region. During this active period some temperature swings are expected, and we’ll be watching closely for the potential for snow and messy mixed precipitation.
Newfoundland and Labrador
Back and forth swings and regular surges of milder air from the south should keep temperatures near normal, but the stormy pattern will affect this region as well, leading to plenty of active weather as December wears on.