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Roger Smith

winter forecast 2019-20: cold comes early but leaves mid-January

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Here's a brief summary of my research findings for the 2019-20 winter LRF.

This looks like being a "front-loaded" winter that changes from a cold eastern regime in Nov-Dec and possibly early January, to a very mild eastern regime for later parts of January and most of February. This trend would likely continue into March, so a lot of the traditional storm opportunity period for the east coast may be removed from play. However, a front-loaded winter can produce its own brand of memorable winter weather too. 

Expect the circulation to be dominated by high amplitude ridge-trough coupling with a gradual retrograde component that will cause the mid-winter reversal. 

The first part of the winter will see frequent incursions of very cold air into the Midwest, Ohio valley, southeastern U.S. and east coast. The storm track will likely run up the coast at times and sometimes from the eastern Gulf to the Great Lakes. Some heavy snowfalls are likely in the eastern half of the U.S. in November and December. Out west it should be relatively dry with a little less than normal coastal rain and mountain snow in general. 

Around early to mid January this pattern will retrograde allowing the storm track to shift to the plains states towards the upper Great Lakes. Temperatures will rebound to above normal values and there could be a blowtorch effect for the east coast at times. Heavy snow in this phase (mid-Jan into Feb-Mar) would be most likely from higher parts of the desert southwest into northern NM, Colorado then northeast to Minnesota. This part of the winter might see anomalous cold, dry spells over the PNW and western Canada with diminished coastal rainfall and some mountain snows but not enough to reach normal values. Analogues include (Jan) 1932, 1937 and 1950, 1968 and 1969, 1986 and 1990..

This pattern might relax at times to allow modified cold to seep into the Midwest and Great Lakes, setting up a secondary storm track from Missouri to upstate New York. This would not cut off the mild air from the coast but might lead to heavy mixed falls inland from Kentucky to northern New England. 

Because the energy level will be high for storm development, some memorable storms could occur. During the colder first half of the winter one or two very heavy snowfalls might be expected in the I-95 corridor. Major blizzards might be encountered later in the winter in the central and northern plains states.

Looking forward to the other forecasts and won't be too surprised if there would be quite a range of options, as the high-amplitude factor means high risk-reward in terms of placement of features and evolution. In other words, confidence not rated as high going into this, but that's the scenario that my research model has indicated. 

Best bet for winter storm on the east coast is Dec 25-26. Best bet for record highs in the warmer portion of winter is mid to late February.

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I used different analogs, but I agree on the mid-winter warm up for the East. The years I picked had the NAO negative in December, neutral in January, then positive February.

More generally, the big warm Sept-Oct periods in the East usually feature some kind of late warm up in winter it seems like.

My pure analogs are actually very cold in December, but I think it will be warmer (somewhat) in the East with Nino 4 near record warmth than the raw blend.

I also agree on a pattern with some huge storms - I think there are somewhere between 3-5 historic storms Nov-Mar nationally, it's just where? Dorian, the recent record blizzard in the NW a few weeks ago, and the relatively rapid shifts in temperature profiles in the Fall all hint at it. I think the culprit for the cold shifting positions is likely the changes in the PDO. It appears to be heading negative, with the cold ring next to Alaska developing around a warm tongue east of Japan right now. The Modoki El Nino look right now is also likely to break down, which favors the West later, as you say.

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