December 23-31 Thoughts: Colder Weather Spreads Eastward

[donsutherland1]

As I continue to look at whether the NAO/PNA forecast (GFS ensembles) can add some value for the distant medium-range (generally 10-17 days out), I will continue to post my thoughts for that timeline. Needless to say, other factors are also considered.

The December 23-31 timeframe is likely to feature the migration of a deepening trough across the Plains and into the East. As a result, milder weather will likely give way to seasonable or below normal readings near or after the 25th. At this time, the pattern does not appear conducive to the kind of major Arctic outbreaks that would bring extreme cold to the Midwest or East Coast. However, both the objective analogs and the GSM suggest the potential for the cooler weather to be fairly short-lived with the potential for a dramatic warmup during the first week in January. The GSM is quite toasty. The key will be whether blocking develops that can help sustain the colder period.

With the return of cooler air will come the potential for at least some snowfall. In the East, the northern Mid-Atlantic to New England should have the best chance with the evolving pattern. The Southern Plains, Central Plains, and Great Lakes region probably have the highest risk of seeing at least an appreciable snowfall sometime in the above-noted timeframe.

My thinking for the average temperature anomalies during the 12/23-31 period is as follows:

Average Regional Temperature Anomalies (12/23-31):
Northeast: Somewhat below normal to near normal
Mid-Atlantic: Somewhat below normal to near normal
Southeast: Below normal
Great Lakes: Near normal
Northern Plains: Near normal to somewhat above normal
Central Plains: Somewhat below normal to near normal
Southern Plains: Much below normal to below normal
Pacific Northwest: Near normal to somewhat above normal
Southwest/Rest of West Coast: Near normal to somewhat above normal

For the major cities from Washington, DC to Boston, the 12/16-22 period is likely to feature:

- Nights generally in the 20s in Boston, New York City and Philadelphia; Mainly 30s in Washington, DC
- Days mainly in the 30s and 40s in Boston, New York City, and Philadelphia; Mainly 40s in Washington, DC
- At least one day with some snowfall from Philadelphia northward and perhaps Washington, DC, too.

In the Southeast, Atlanta will likely see highs generally in the 40s and 50s. Lows should generally be in the 30s. Detroit may see no 50° or above readings. There, highs will be in the 30s through much of the period and that city has a good chance of seeing accumulations of snow (the potential exists for an appreciable or greater snowfall given the pattern).

[Lowpressure]

Don, I think you may have the incorrect bold dates in the later part of your forecast. Great job as usual, what do we in the East have to do to get a winter storm? It seems like every forecast that comes out there is less chance of winter. No, this is not a winter cancel post, but wow something winterlike would be nice.

[donsutherland1]

Thanks Lowpressure. I've fixed the dates. Often, El Niño winters have had their coldest/snowiest weather in either January or Feburary.

[southerngale]

Thanks Don...I always appreciate your posts.

[DESTRUCTION5]

Hey Don as always Fantastic Job on the forecasts...Whats your thoughts on snow chances in the ashville area Xmas week?

[Stephanie]

It'll be nice to have Christmas FEEL like Christmas up here. I'd like to put an order in for a snowflake or two on Christmas Day please.

The warm weather has been great this week, except for the dang FOG!! It's like pea soup in some places.

[donsutherland1]

Thanks Kelly and Stephanie.

It certainly will be nice to see some cooler weather and snow. The GFS is trying to deliver a shot of post-Christmas snow, but the details can change significantly given the timeframe involved. As for tonight, the fog blocked out any possibility of seeing the Aurora.

[donsutherland1]

DESTRUCTION5,

With a more active southern jet, I'm reasonably confident that the southern U.S. could see at least one precipitation event in the 12/24-30 timeframe. Whether such an event might bring snow to Asheville remains to be seen.

[Miss Mary]

Thanks for the headsup. I've been putting off buying new tires and we're pretty sure my front brakes need to be replaced. We'll verify that when the tires go on......I knew winter would return up here. This warm spell will not last. Time to make that tire appt.

[CaptinCrunch]

This pretty much sums it up....

THE PNA INDEX WHICH RECENTLY HAS BEEN POSITIVE IS FORECAST TO REMAIN POSITIVE THROUGH DAY 14. THE NAO INDEX WHICH RECENTLY HAS BEEN STRONGLY POSITIVE IS FORECAST TO TREND TOWARDS ZERO BY DAY 7 AND REMAIN NEAR ZERO THROUGH DAY 14. AS A RESULT OF ABOVE NORMAL HEIGHTS MUCH OF THE NORTHERN HALF OF THE CONUS IS EXPECTED TO EXPERIENCE NEAR TO ABOVE NORMAL TEMPERATURES. THE TROUGH FORECAST OVER THE CENTRAL CONUS AND ITS ASSOCIATED AREA OF BELOW NORMAL HEIGHTS IS LIKELY TO BRING NEAR TO BELOW NORMAL TEMPERATURES FOR PARTS OF THE SOUTHWEST CONUS. SOUTHERLY FLOW AHEAD OF THE CENTRAL U.S. TROUGH SHOULD CAUSE ABOVE NORMAL PRECIPITATION FOR SOUTHERN FLORIDA AND FROM TEXAS EXTENDING NORTHEASTWARD TO THE LOWER MISSISSIPPI VALLEY AND MID-ATLANTIC STATES. THE FLOW AHEAD OF THE TROUGH FORECAST OVER WESTERN ALASKA WILL LIKELY LEAD TO ABOVE NORMAL PRECIPITATION FOR PARTS OF SOUTHERN COASTAL ALASKA AND THE ALASKAN PANHANDLE. SUBSIDENCE ON THE REARSIDE OF THE CENTRAL U.S. TROUGH WILL LIKELY LEAD TO BELOW NORMAL PRECIPITATION FOR MUCH OF THE WEST/CENTRAL STATES.

[Dean4Storms]

The 12z GFS depicts a very cold artic ourbreak across the west sliding into the plains and into northern Texas come 1st of Jan.


http://wxweb.meteostar.com/models/misc/ ... _sfc.shtml

[JonathanBelles]

it now shows rain for christmas

[bob rulz]

Don, I was wondering what you see for the Salt Lake City area here?