My Winter forecast included a colder than normal December through mid January, but that has obviously been a BIG error. December temperatures have run five degrees above normal. What’s been driving that is the lack of a -NAO and -AO. This is partially due to a powerful low pressure vortex that has been anchored in or near the Gulf of Alaska, and the inability of the Madden Julian Oscillation(eastward moving tropical disturbance in the Indian & Pacific Ocean areas, that influences Eastern North America Wintertime temperatures) to move into the phase required. Signs are now evident that the powerful vortex in Alaska will move to the west and southwest, and the MJO is moving into favorable phases to support a change in the weather pattern to the Wintry pattern I anticipated in December. This would promote a transition to a -NAO and -AO, and much colder and stormier conditions COULD become locked in, just as the mild regime has been in place for several weeks.
Even in this mild pattern, one thing that has been in place recently, is a +PNA pattern, that has supported ridges in the western US. This index is forecast to strengthen, which would eventually lead to eastern US troughs. Currently, the European model and Canadian model are forecasting a monster trough amplification early next week, and the GFS shows the same configuration the following week. This is an obvious sign of the pattern change that is finally ongoing. Will the change lock in or will the pattern revert back? I’m not sure, but I think the pattern should change to a more amplified(cold outbreaks and major storms) pattern for at least a few weeks, and possibly well into February. Essentially, my Winter forecast would move forward one month, and the cold I anticipated from the beginning of December to the middle of January would occur from the beginning of January to the middle of February.
Another aspect of the late Fall and early Winter, to this point, has been a prevalence of cut off upper level low pressure centers. As the possible amplification(deep troughing in the eastern US – bottom of roller coaster) forms early next week, the European model forecasts a powerful cutoff low pressue system combining with a major cold outbreak. This would potentially result in a major snowstorm for the South, and up the Eastern US coastline. The GFS model is showing the same amplification a week later. Please see attached links for images. If this amplification takes place, the mild early Winter we have experienced will be a faint memory……….
Note the (7) contour(height/pressure circles) upper level closed low on the European forecast for hour 192(next Wednesday morning). This would pull down very cold air from the upper atmosphere in conjunction with Arctic air being brought down by a strong area of high pressure dropping down from Canada. On the colored image, notice the very cold temperatures(-10 to -15 C) at the 5000 foot level. This would mean very cold surface temperatures(teens and twenties F). In combination with this, I would anticipate an area of low pressure to develop in the Gulf of Mexico and move northeast near the Georgia/South Carolina coastline, bringing the potential for snow. The details will become clearer over the next few model runs. Obviously, this could completely change, but the amplification the model shows is likely sometime within the next 7-10 days. Maybe not this dramatic, but something similar. Could just mean a change to cold temperatures, or could be much more Wintry! I’ll keep you updated.