13 January 2014

Don’t Let The Thaw Fool You, The Revenge of The Polar Vortex May be Coming

Posted by Dan Satterfield

An ensemble of numerical weather nodel runs are indocating the polar vortex may be dragged back down into the NE U.S by a frigid blast of air next weekend. Each model run on this chart is shown by one red, blue and green line.

An ensemble of weather model runs are indicating the polar vortex may be returning to the NE U.S by next weekend.

Numerical weather models tend to become very unreliable beyond 5 or 6 days but meteorologists have discovered a trick that helps in long-range forecasting. At least a bit. We still cannot pin down what day a storm will hit at a particular place but we can get a good idea of whether or not the pattern will be warm/cold/dry or stormy.

Here is the trick: Run the weather model multiple times using very slightly different starting points. To use physics and maths to model the atmosphere we have to give the model a starting point, and since we do not know the exact temperature pressure etc over every square kilometer of the planet, we have to do a best guess. Since weather is chaotic and follows chaos theory, a small change at the start will lead to major differences as you go out farther into the future.

 

12 days from now the agreement between the runs is much worse, but you can still see that there is a deep trough of cold air indicated in the eastern half of North America.

12 days from now the agreement between the runs is much worse, but you can still see that there is a deep trough of cold air indicated in the eastern half of North America. The yellow line is the average of all runs. I’m working on a blog post about just what the polar vortex is and it will be posted in a day or two! Each model run on this chart is shown by one red, blue and green line. This is the European Global Model run by the ECMWF in London.

For five to 10 days however, you will usually see that most of the model runs tend to be pretty close with a couple of outliers. The differences magnify with time, but taking an average of the models can yield some surprisingly good information. Studies have shown that this method is more accurate on average than using one or two models, and it is now being used in hurricane forecasting, severe weather threats, and rain and snowfall forecasting.

The NOAA Long range model also indicates well below normal temperatures over the East in 10-14 days!

The NOAA Long range model also indicates well below normal temperatures over the East in 10-14 days! (From WX Bell model site which we could not live without in the WBOC Weather office!)

Forecasters call all these model runs the ensemble and we even have short-range and long-range ensembles now.

So, with this in mind, I can say with some confidence that the cold in the Eastern U.S.A is about to return. Initially it does not look as severe as this last batch and that makes sense since we have drained most of the really frigid air out of the High Arctic…for now at least.