© 2019 Terry Swails

EARLY SNOWS, WHAT IT MEANS FOR THE WINTER....

October 25, 2018

We're down to the last week of October and so far the month has been cooler than normal. Tuesday night was the 5th time in 24 days with a low in the 20s here in Cedar Rapids. The month currently is the 2nd coldest for highs since 1981. Pretty impressive.

The bulk of the real cold has come in the past 14 days. Much of Canada and the central U.S. far below normal.

With the cold has come snow. Much of the central and upper Midwest has had a taste. In parts of my local area some places have already seen snow on 3 different occasions. Below you can see what's accumulated over the nation since October 1.

As of today, most of what's accumulated has melted in the U.S. Only 1.4% of the nation remains covered. This is what remains. Canada off to a good start to the season.

A tighter perspective. 

Globally snow cover looks like this.

The greatest surplus is found in eastern Canada.

Notice fall snow cover is near to below normal in Siberia. The National Science Foundation (NFS) is investigating the relationship between Siberian snow cover in fall months, and Northern Hemisphere climate variability during the winter. According to their research, below normal Siberian snow cover in October is an indicator of an increased probability of a strong polar vortex at northern latitudes and a predominantly positive Arctic Oscillation during the winter. The end result would be mild temperatures over the nation, especially east of the Mississippi. The NFS winter temperature forecast.

To reach this result the NFS forecast is based on the AO (Arctic Oscillation) being predominately positive during winter. In the graphic below you can see the differences between a positive and negative AO. The positive AO and its temperature correlation is shown across the top. The blue indicates below normal pressures at the 500mb jet stream level across the Arctic and Canada.

I can already say I have doubts about the accuracy of the NFS forecast when 3 of the best models I use show the opposite. I'm putting up the winter outlooks from the EURO, JMA, and Joe D'Aleo's Pioneer model. All of these show higher than average 500mb heights across the Arctic and Canada. That implies a negative Arctic Oscillation this winter. A negative AO brings cold to much of the country east of the Rockies, just the opposite of the NFS forecast. Note the absence below of any blue color in the 3 models over higher latitudes such as Canada.

 

Suffice it to say, nobody really knows how it all plays out. It's pick your poison and for me the smart money is on the better physics of the EURO and multiple drivers built into the Pioneer. They have me believing there will be cold this winter, especially from the central U.S. east. The big question to me is where the western N. America ridge sets up. The further west the greater the chances for significant cold and snow across the Midwest. If things don't get cranking by late November I'll be concerned. Meanwhile, there's a good 3-4 weeks to monitor trends. Roll weather and negative AO...TS

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