Changing pattern could lead to multiple storm threats
We warned you that this was coming. Now, the pattern change is finally beginning to appear on medium and long range model guidance from late December into January. Thanks in part to changes in the stratosphere and retrograding mid and upper level atmospheric features, the pattern over the next week or two will become much more favorable for not only colder than normal air, but winter weather in our area as well. Contrary to what it may seem, the pattern currently is quite unfavorable for cold air and winter weather. Warmer than normal air has settled in to Southern and Central Canada over the past week or so, muting any potential shots of cold air with northwesterly winds.
But the notable feature around the Northern Hemisphere will begin retrograding over the next several days. It begins with the troughiness over the Gulf of Alaska and ridging in the Eastern Pacific. Both of this features will progressively retrograde westward over the next 7-10 days. The end result will bring a mean trough to the Aleutian Islands and a ridge to the West Coast of the United States and British Columbia (also known as a +PNA). Further securing the changing pattern will be the development of a +EPO ridge in Western Canada and the potential for ridging to develop over Eastern Canada, Greenland and the Western Atlantic.