Seasonal Upper Air Pattern Transition Underway

Thanksgiving for me tends to start the period where the atmosphere and the upper air pattern begin to transition into what will be the winter pattern. It seems to me that this time of year we see a morphing of the upper air jet stream which will eventually lock in to what will be the winter. What that pattern is we don’t know yet. It might be the one we have at the moment with blocking combined with a fast west to east jet across the US with little amplitude. Cold shots come in and out every couple of days followed by brief warm ups. That is what we have at the moment. There has been a lack of storm activity across most of the nation for the last few weeks. Right now there is no sign of this part of the equation changing.

SEASONAL UPPER AIR PATTERN CHANGE TEMPERATURE ANOMALY NEXT 10 DAYS CLICK TO ANIMATE

One of the interesting things about the loop of the temperature anomaly (below or above average) map is that there is a large part of the Northern Hemisphere that is showing below average temperatures. The other interesting factor is that the polar region is warmer than average which argues for a continued displacement of the jet stream south of average. This is quite a change of the prior 2 winters and continues to argue that the atmosphere is “normalizing” to some degree.

EUROPEAN MODEL JET STREAM NEXT 10 DAYS

CLICK TO ANIMATE

Among other things, when we loop the European jet stream you will notice that the blocking high over Greenland doesn’t last long however as the first upper high develops and disappears a second upper high begins to build in the Atlantic toward Greenland at least according to how the European model sees the world. The persistence of higher than normal pressures in the North Atlantic is something we will need to pay attention to. It also appears that the flow across Canada changes somewhat later in the period where we are not seeing strong vortex’s dominating the upper pattern there. It also appears that the Pacific jet part of this puzzle is changing a bit with some systems beginning to push eastward. Overall the upper pattern seems to evolve into a bit of an unorganized mess as we head into December. One thing we can say that at least through the next 10 days, there appears to be no major concerns.

EUROPEAN WEATHER MODEL MONDAY 11/27/2017 FORECAST LOWS

The next important cold shot will come next weekend as a cold front drops southward. The upper trough with this looks fairly deep so the shot of cold air will be fairly robust for Sunday through Tuesday of next week. Lows in the 20s could reach as far south as Northern Georgia & Alabama with 40s into South Florida. None of this is coming however with any major storm development. Snow fall in the Northeast will be confined by lake effect events with the next one coming next Sunday into Monday. Other than that it appears that the month will come to an end quietly.