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Sam Has Some Tough Competition - This Will Be Interesting

Message from Tom in Philadelphia

I still don't think seasonal forecasts have much confidence overall, but Sam you do think they are now better than before so I though I would post this.

Dr. Judah Cohen is at odds with your winter forecast. He calls for a mostly negative AO, and a colder than avg winter for the South and Eastern US. He call for above avg snow in the Mid Atlantic, which with that snow cover allows for colder temps in the SE US. Last winter some of the coldest anomalies in places like Norfolk and NC happened when there was snow cover to the north. He says Dec will probably be milder, but then Jan and Feb much colder.

He claims to have a 75% accuracy rate, so I'm sure Joe Bastardi will be all over this. Seems he and JB are the two most prominent seasonal forecasters calling for a colder than avg winter. Dennis has some prominent company on this one.


Our research has shown when Eurasian October snow cover extent or the Snow Advance Index are above normal, this favors a negative phase of the winter Arctic Oscillation (AO) or weakened polar vortex, most often in January.

I do expect in December and January a weakening of the polar vortex, followed by an extended period where the AO is predominantly in the negative phase.



This part doesn't sound good at all for the South or Mid Atlantic:


CWG: Do you agree with the idea that it will be cool in the South and mild to the north (compared to average) as predicted by some models and the National Weather Service?

JC: In principal, I would agree with that general temperature pattern. However, I do believe that if the polar vortex is weak and the AO is negative in mid-winter, the cold in the Eastern U.S. will be more widespread than predicted by all other forecasts that I have seen.



This part of the interview was interesting as I have heard this before. That the warming Arctic is forcing really cold air much lower in latitude than in the past:


CWG: Because this El Niño is so strong, close to a record, could it overwhelm the effects of the Arctic Oscillation — like in 1997-1998 when the AO was negative but it was mild with little snow?

JC: This is a great question and one that I am finding a really tough challenge. Don’t think the 1997-98 scenario isn’t running through my head every day. El Niño did seem to triumph that winter and, of course, a repeat is possible. However, I do believe our climate is sufficiently different that a repeat of 1997-98 is less likely today.

The Arctic is much warmer today than it was just twenty years ago and with much less sea ice not only in extent but especially volume. This is a controversial topic but I do believe and quite strongly that a warmer Arctic is forcing colder winters in the mid-latitudes. In 1997-98, it was cold across much of northern Eurasia and even northern Canada. I think if we were to have a repeat of 1997-98, the much warmer Arctic of today would favor a southward displacement of the cold.



Who would have thunk that global warming (not saying it is true, but the Arctic has for certain warmed), would make us colder in winter. Go figure.

Overall his temp anomalies are not that bad and close to average, however, with a warm December the Jan and Feb anomalies would be a bit colder than these numbers. He has a departure for mean Dec, Jan, Feb temp of around -0.5F for Philadelphia, -.6F for Savannah, -.4F for Mobile, AL, -1F for South Texas, -.4 to -.2 for Central and S. Florida, etc.

Overall this winter wouldn't be bad with his numbers, as long as the extreme cold is short lived, and we don't have zone busting temps.








https://www.washingtonpost.com/news/capital-weather-gang/wp/2015/11/24/innovating-forecaster-highlights-potential-for-very-snowy-winter-in-mid-atlantic-d-c/


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