Elliot Abrams

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Major Cold Shots Coming Next Week and Again the Week After

January 16, 2014; 8:51 AM

Thursday morning

The video includes a discussion covering the period from today through the weekend.

Looking ahead, the main U.S. model, the GFS, shows major cold waves invading the Great Lakes, Northeast and even most of the South next week, and then again the following week. This map for Jan. 30 shows what this could look like. Focus on the (typical) snow-rain line, which is the dashed line with the darkest blue. The dashed blue lines north of there are lighter, and to the south there are red dashed lines. Now look at the isobars, the black lines. These are oriented north to south all the way from Kansas to Ohio. What this means is that as cold as it is already, more cold air is still arriving!

HOWEVER, the models are run many times with slightly different inputs. The resulting ensemble can show huge differences in the longer ranges. This map, which only shows the lines for predicted temperatures of +10 degrees Celsius and -10 degrees C, shows such a situation:

The first map above is just one map from the ensemble set, whereas this second map has all the solutions represented by differently colored lines. Think of a music ensemble. The flute player and drummer play different parts. No one instrument represents the entirety of the music being played (unless it is being played by a soloist).

If you consider all the forecast versions from all the model runs, you can get an idea about whether there is a forecast idea that most of the members support. The exceptions to this majority solution are often considered to be outliers. They are helpful in showing what can go wrong and thus minimize the chance for a total surprise.

You can also get a map showing the mean flow. Such a map incorporates information from each individual member of the model ensemble. While that can be useful, it often has a drawback: by averaging out all the differences, you may lose the extreme event or get a badly toned down version of what may actually happen. To highlight the differences, spaghetti plots are generated. These consist of lines for a specific value, such as the line along which every place is 10 degrees. When you look at all the lines for forecasts of this value 10-15 days out, it starts to look like spaghetti.

The views expressed are those of the author and not necessarily those of AccuWeather, Inc. or AccuWeather.com


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About This Blog

Elliot Abrams
Elliot Abrams from AccuWeather.com offers this Northeast Weather Blog for the U.S. with regular updates on NE weather from a leading forecaster and meteorologist.