Posted: 9:00 am Tuesday, November 22nd, 2016
By Kirk Mellish
I have to start by saying that I have lower than usual confidence in this long-range forecast for winter. There simply are two many signals that are either weak or contradictory. Some suggest quite cold for us, if not cold and wet. Others suggest warm or just neutral.
In addition, the overall pattern of atmosphere indices and ocean sea-surface temperature patterns are sufficiently in variance with anything in the previous record that finding strong analogs to use has been an uphill climb.
This seems to be underscored by a casual survey of my colleagues around the country as there is a definite split between very warm outlooks for the south and east and much colder than normal ones.
Most of the computer models are warm and dry for the Southeast, and in fact for much of the nation for the coming winter. But I find their track record too weak to give them much weight in my outlooks.
For a further explanation of the analog technique please read the previous preliminary winter outlook. In brief, an analog year is a past year that had conditions in the oceans or otherwise, similar to what we had or are having now. By looking back one then can try to project ahead.
For simplicity’s sake I’ve left out most of the heavy science here as it was covered more in the preliminary outlook and many other blog posts over the past decade or so.
But when possible, and as much as possible emphasis is placed on all the oceans equator northward, because that’s where most of the energy to drive the atmosphere is located.
The “consensus” analog list is as follows:
1928, 1950, 1954, 1955, 1959, 1960, 1961, 1962, 1964, 1966, 1967, 1971, 1975, 1980, 1983, 1984, 1990, 1995, 1996, 1998, 2000, 2005, 2006, 2008, 2011, 2012, 2013, and 2014.
From these the “Best-fit” analog years are:
1966, 1983, 1995, 2005, 2008, 2013 and 2014. 83 and 95 are two of the strongest matches.
Both of those winters were cold, 1983 had 10.3 inches of snow but 1995 had just 0.4 inches.
The average snowfall in the first list was 1.67 inches. The average snowfall in the best fit list was 2.88 inches. The average snow in all the analogs I considered was 1.9. The range was from zero to 10.3 inches.
Because meaningful snow accumulation is so rare in Atlanta the mean from analogs doesn’t really tell us much because it so often will end up near the historical norm which is around two inches. Yet so many winters have a trace or none. Thus any amount over 4 inches will easily skew the outcome of the analog data.
Our best odds for a snow IF there is to be one at all, would seem to come January-March, which is par for the course. Keep in mind December snow of consequence is highly unusual here.
Indicators for an early start to winter vs. a late cold period are largely split so no clear guidance.
Despite having reasons to believe recent El Nino and La Nina’s would behave differently than the composite example from the past, they have in fact played out pretty close to classic. When you combine that with the recent warming decadal trends, it gives me pause to go with a colder and snowier outlook as might be suggested by the analogs and the indicators that give rise to them.
Thus I will modify the pure analogs to make my final call.
I expect temperatures to average near-normal December-February with come and go colder than normal and warmer than normal spells. I expect wintertime precipitation to average near-normal to below-normal. Remember this is the 3-month mean not every day or every week or every month.
Favored jet stream storm tracks for winter precipitation:
Snowfall I expect to be less than normal. Odds for ice look average.
My gut tells me that if my outlook is wrong, it’s more likely to be colder than I expect and wetter than I expect.
Normal or average yearly snowfall across the nation:
The highest confidence for a warm winter is west of the Rockies. The highest confidence for a colder than normal winter is the northern plains and upper Midwest.
Highest confidence for above average precipitation is the Upper Midwest Great Lakes and Ohio River Valley.
Obviously if the sea-surface temperatures patterns shift it will shift the odds of one type of winter over another, and if I see that I will update the outlook. Follow me on Twitter @MellishMeterWSB.