North Atlantic Oscillation Driving Models Crazy
North Atlantic Oscillation Driving Models Crazy
There is no doubt about the fact that the models are being driven crazy by the North Atlantic Oscillation or blocking. Every run deals with the magnitude and position of the rising pressures and a possible blocking high in the North Atlantic differently This creates ridiculous volatility in the weather models beyond day 7 in the long range. This of course creates chaos on the pattern and how it evolves. The last 24 hours continues to show this back and forth trend and has made coming to grips with the long term outlook extremely difficult.
NORTH ATLANTIC OSCILLATION INDEX
The index that measures the magnitude of the North Atlantic Oscillation is off the wall negative. When the index is negative it means that pressure across the North Atlantic are higher than normal and in this case much higher than normal. Usually the N.A.O. means colder than average temperatures in the Eastern US but not always. At the moment the “block” is “east based” which favors cold air into Western Europe. There are also other factors which are favoring average temperatures in the East with quick shots of chilly air and short warm ups of a day or so with very little precipitation. This will continue through this coming weekend. We have a cold front coming with some showers Thursday night into Friday morning which won’t amount to much. We also have a weak system that will develop just offshore on Sunday which could bring clouds and maybe a little rain for coastal areas. Other than that we wait until the middle of next week when the N.A.O. index begins to rise toward neutral. This could be an indication of an important change and when combined with other changes across North America, could be indicating a storm signal of some kind in the Eastern US. All of this at this point is speculative. It doesn’t guarantee anything of consequence but it is something to watch.
PACIFIC NORTH AMERICA PATTERN INDEX
Another index that is important is the Pacific North America pattern index which is going strongly positive next week. This is indicating a ridge in the west that would be an important ingredient to any potential activity in the Eastern US. A strong ridge is supportive to something developing in the Eastern US of importance.
All of this makes the puzzle that lies ahead more intriguing. Weather models today continue to struggle with all this as models continue to react to the impact of the North Atlantic Oscillation. Once again today models trend colder after day 8 which would start a week from tomorrow. Once again today the models are completely different in how they handle the blocking.
GFS FORECAST FRIDAY DECEMBER 8TH
The GFS today develops an incredibly strong upper high in Northeastern Canada which displaces the polar vortex to the south over the Great Lakes. The result is cold air pouring into the east in a broad fashion. This basically would be cold and dry.
EUROPEAN MODEL FRIDAY DECEMBER 8
It seems that the trend to colder than average temperatures beginning around the middle of next week is a given on both models. Whether it comes with any precipitation is another matter. You can expect the models to continue to show long range volatility and lots of forecast uncertainty until we can settle just exactly what is the blocking high going to do.
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