Active Weather Continues Ahead of Expected Pattern Change

Sunday, December 14, 2014, 8:00 AM - A pattern change seems likely, but a tricky transition could mean forecast challenges for late December.

With less than half of the month gone by, December’s active weather has already made a big impression across Canada. And it looks like that trend will continue into the long range. Indications are that we’re in for a bit of a shake-up, as the pattern shapes up that will take us into the New Year.

Looking ahead to the week leading up to Christmas, there are signals that we will be dealing with the potential for a developing storm, with impacts from southern Ontario through the Maritimes. Behind it will come changes that will dry out the BC coast, and bring the return of arctic air to the East.

There is good agreement among the models that a surface low pressure area will develop along the Gulf Coast late next week, in response to an upper level trough. From there the storm will track north into the Ohio River Valley, and as it wraps up will spark the development of a new low pressure center off the East Coast of the US, which will continue on through Atlantic Canada.

The forecast challenge for this system will be the exact track of the low, and particularly the timing of the storm`s approach. As of now, it looks like the primary impacts to Canada will be early in the week, but the potential exists for the system to develop more slowly, which would increase the affects on Christmas travel.

After this system departs, the models are in good agreement that we will be set up for a pattern change for the last week of December, which will strongly influence the weather into the first part of the New Year.

This image shows the forecast upper atmospheric "landscape" on December 28. There are a couple of important features to take note of, which have implications for the type of weather that we can expect.

British Columbia is under the influence of a strong ridge, which would make the case for warmer and much drier conditions. The formation of this ridge is supported by the current sea surface temperatures in the Northeastern Pacific, which are much warmer than normal.

The amplification of this ridge is paving the way for the development of an impressive trough, which will overspread much of the interior. This trough would allow for large-scale northerly flow, and the southward expansion of arctic air. 

In short: this is a cold and stormy look for the East going into 2015.