December 2017 Discussions & Observations Thread

[Paragon]

4 minutes ago, uncle W said:

from 1976 to 1985 there was some of the coldest January's and winter minimums...the three years that didn't have record cold were el nino years...the other one was 1976-77 that was very cold...77-78 was very cold but never did get into the single digits...the only great winter was 1977-78...Feb 78 and 79 are the only two cold  ones...

...-1 in 1975-76

...-2 in 1976-77

..10 in 1977-78

....0 in 1978-79

..10 in 1979-80

...-1 in 1980-81

....0 in 1981-82

..12 in 1982-83

....4 in 1983-84

...-2 in 1984-85

Oh that's the other thing I remember, very cold Januarys but February was almost always much milder and above normal.

 

[doncat]

0.58" for the day...High temp 49 degrees.

[Morris]

High of 48 today in the park. The "torch" day.

[donsutherland1]

1 minute ago, Morris said:

High of 48 today in the park. The "torch" day.

It could have been worse. Yesterday was 50°. As nearby as Atlantic City saw a high temperature of 60°. Parts of Virginia were in the 70s.

[snywx]

35° and breezy

[CIK62]

Next 8 days still averaging 27degs., or about 8degs. BN.

DEC. should finish at 1.6degs. BN.

[bluewave]

We got our usual warm up around the solstice  with 4 days reaching 50 since the 18th around the area. 57 was the high when we had more sun on the 19th. This boosted the departures to positive territory on the month. But the Arctic cold this week will drop the departures back to below normal for December.

NYC...+0.6

LGA...+1.2

JFK...+0.2

ISP...+0.9

BDR...+0.9

EWR...+0.9

[CIK62]

Meanwhile our fading 12/29-30 snowstorm, seems to need a stronger SE Ridge or a stronger ridge in the Pacific NW, which looks flatter than 2 days ago. 

 

[SACRUS]

 

Dec departures thru 12/23 - looks all below from here

PHL: +1,4
LGA: +1.2
TTN: +0.9
EWR: +0.9
NYC: +0.6
JFK: +0.2
 

 

 

[donsutherland1]

This morning, the AO was a preliminary +1.088 and the monthly average is up to -0.047. So far, 25% of days were at or above +1.000 and 25% were at or below -1.000. It is forecast to go somewhat negative in coming days in combination with a positive PNA. Such a pattern is typically associated with elevated prospects for snowfall during the second half of December. The following statistics are available for the December 16-31, 1950-2016 period:

Daily measurable snowfall: +41% above all cases without an AO-/PNA+

Daily snowfall of 2" or more: +39% above all cases without an AO-/PNA+

Daily snowfall of 4" or more: +78% above all cases without an AO-/PNA+

Monthly Mean Temperature for NYC Through:
12/23 39.2°
12/25 39.0°-39.2° (12/22 estimate: 38.8°-39.6°)
12/31 35.4°-36.8° (12/22 estimate: 35.4°-37.5°)

Estimated probability of a below normal monthly anomaly: 67% (12/22 estimate: 59%)

The 0z GFS MOS forecasts a high temperature of 23° on 12/28 and a low temperature of 14° on 12/28 for New York City. The last time the high temperature was at least as cold in December was 12/14/2010 (23°). the last time the low temperature was at least as cold was 12/22/2008 (13°).

It remains likely that an area running from Philadelphia to Boston will see monthly total snowfall of 8" or more. The potential for a 6" or greater snowstorm in the Middle Atlantic and southern New England regions remains above the climatological probability, even as that probability has fallen in recent days (in connection with a forecast for a flatter PNA ridge and reduced AO blocking).

Any moderate or larger snowstorm near the end of this month is likely to usher in a period of severe cold, which should linger into the first week of January. During this period of severe cold, the possibility of at least one single-digit reading exists for Philadelphia, New York City, and Boston. North and west of those cities, single-digit and possibly subzero lows are likely.

Afterward, the EPO will likely go positive and the AO could go strongly positive late in the first week in January. The result should be a retreat of the cold and a pause in snowfall opportunities in the Middle Atlantic region and possibly at least southern New England.

However, a fresh EPO ridge could begin to rebuild afterward and a strong vortex in the AO region could fade. This idea is premised on the assumption that winter 2017-18 will evolve as has often been the case with snowy Mid-Atlantic and southern New England winters. Such a pattern evolution would suggest that the relaxation of winter would be temporary. If so, cold and opportunities for snowfall could return at some point during the second half of January following the pattern relaxation.

In the meantime, the northern half of Westchester County northward will likely pick up an inch or more of snow from tonight into tomorrow morning. Orange and Dutchess Counties out across northwestern Connecticut have the potential to see 2"-4". So, at least parts of the region will likely experience a white Christmas.

[CIK62]

Isn't the 12Z EURO predicting record low 500mb heights  [under 5000m]  and a record low 850mb temperature [-25C]  here @12Z Dec. 31.    That should give us some sort of Sub-Zero 2M temperature , which I do not see elsewhere.

 

[NEG NAO]

Precip has begun as snow in Northern Middlesex County NJ

 

https://www.wunderground.com/weather-radar/united-states/pa/philadelphia/dix/

[The Plowsman]

Raining nicely in ctrl Monmouth County. Home of the snow sweet spot of the tri-state! Merry Christmas to All!

[Snowman86]

Merry Christmas everyone.

[Rtd208]

Had some light snow falling here a little while ago, current temp 37

[AfewUniversesBelowNormal]

The Polar Vortex in Canada isn't moving right now. fwiw

[CIK62]

Next 8 days down to 23degs., or 12degs. BN.

Maybe 12"+ snow by early in the New Year on the ground>>>by the GFS.  CMC more into the low temps than snow right now; how about averaging 15degs. for a five day period!

Either way...........................

HAPPY HOLIDAYS!

[Rtd208]

Light snow falling here, temp 34

[CIK62]

I just remembered something Tex Antoine would mention with this cold spell.....that the one exactly 100 years today started on Christmas PM too and continued to Jan. 06 or so (but 7 or 10 degrees colder, I'd say)

Anyone have the actual numbers?  Please post.  Thanks.

[rgwp96]

1.5, butler nj 

[ForestHillWx]

1/2" of a Christmas miracle on the ground. All the pines are trimmed nicely in white. 

 

Merry Christmas everyone!

[weathermedic]

Winds gusting in the 40 mph+ range around NYC with a few 50 mph+ across Long Island. Nantucket gusted up to 63 mph in the last hour.

[CIK62]

44 minutes ago, bluewave said:

Pattern relaxation on track for after Jan 7th. The forcing which has resulted in the strong -EPO  is starting to shift west. This should produce a more typical La Nina response. We'll have to see of the forcing can migrate east toward the DL later in Jan or Feb for another -EPO interval. While it may not be as strong as we have seen during November and December, it could be enough for more snow chances.

 

 

 

 

I am not sure I am reading this correctly, but isn't the strongest lifting going east (lower western longitude numbers)   Either way, your point is that it is moving away from the DL for now.

[doncat]

Wind really roaring today...had a gust to 47 mph at nearby mesonet.

[The Plowsman]

My Holly says GL clipper Fri Not going to phase with GofM low for the "significant snow" as of 12:30 pm.

[CIK62]

Next 7 days down to an average of 21degs., or about 14degs. BN     The average cut will be 16/25,  L/H

[Paragon]

8 hours ago, bluewave said:

Pattern relaxation on track for after Jan 7th. The forcing which has resulted in the strong -EPO  is starting to shift west. This should produce a more typical La Nina response. We'll have to see of the forcing can migrate east toward the DL later in Jan or Feb for another -EPO interval. While it may not be as strong as we have seen during November and December, it could be enough for more snow chances.

 

 

 

 

Think our biggest snow event of the season comes at the end of the first week of Jan, Chris, right before the pattern flips?

[Paragon]

8 hours ago, weathermedic said:

Winds gusting in the 40 mph+ range around NYC with a few 50 mph+ across Long Island. Nantucket gusted up to 63 mph in the last hour.

Highest wind was 73 mph on Cape Cod I think.

I saw some videos of an intense burst of snow at Logan Airport, did they get 4 inches of snow in one hour?

[AfewUniversesBelowNormal]

I see the high heights in the North Pacific on long range models as just big waves breaking on the mountains at higher than average frequency. 

It looks like -PNA but it's likely not. 

http://mp1.met.psu.edu/~fxg1/ENSHGTAVGNH_0z/ensloopmref.html

[donsutherland1]

This morning, the AO was a preliminary +0.433.  It is forecast to approach 0.000 in coming days. A cluster of ensemble members take the AO negative. Another cluster favors positive values. Through December 26, the preliminary AO average is +0.012 and 58% of days have seen negative AO values. That is both the lowest average and highest percentage of negative AO days through 12/26 since December 2012. In fact, December 2013, 2014, 2015, and 2016 saw 73% or more days with AO+ values (96%, 73%, 85%, and 81% respectively).

For the first time this month, the PNA has gone somewhat negative (-0.167). The dip is forecast to be temporary, with strong agreement among the ensembles that the PNA will rise to +0.500 - +1.000 in a few days.

Taking into consideration the expected temperatures, a PNA+ pattern would favor a higher probability of days with measurable snowfall and snowfall of 4” or more than climatology for the 12/25-1/10 period (1.6X and 1.2X the climatological norm for the January 1950-December 2016 period). The probability of measurable snowfall would be approximately 18.7% for the 12/29-1/7 period (or an expected 2 days with measurable snowfall). Should the AO go negative, the probability of days with measurable snowfall and snowfall of 4” or more would increase to 1.9X and 1.4X climatology for that timeframe).

Through December 25, the monthly temperature anomaly was +0.6°. However, the long-expected cold pattern has now set in. A period of potential severe cold peaking with single-digit readings in New York City (0z ECMWF and 0z/6z GFS) and subzero readings in many of the suburbs appears likely during the opening days of January. All said, December will likely finish with a cold anomaly.

Monthly Mean Temperature for NYC Through:

12/25 39.0° (12/24 estimate: 39.0°-39.2°)
12/31 35.1°-36.1° (12/24 estimate: 35.4°-36.8°)

Per aggressive sensitivity analysis, the estimated probability of a below normal monthly anomaly: 76% (12/24 estimate: 67%)

The 0z GFS MOS forecasts a low temperature of 12° on 12/28 and a high temperature of 20° on 12/29 for New York City. Both such readings would be the coldest December low and high temperatures in more than a decade. Below are the coldest December high and low temperatures in recent years:

Low Temperature:
20°, 12/15/2017
17°, 12/16/2016
16°, 12/29/2009
13°, 12/22/2008
12°, 12/21/2004
11°, 12/20/2004
10°, 12/27/1993
  8°, 12/27/1989

High Temperature:
28°, 12/15/2017
27°, 12/16/2016
23°, 12/14/2010
21°, 12/20/2004
20°, 12/27/1993
18°, 12/22/1989

Considering the forecast pattern, it still remains likely that an area running from Philadelphia to Boston will see monthly total snowfall of 8" or more. With yesterday's 2.9", Boston's monthly snowfall has already surpassed 8" and currently stands at 9.1". The potential for a 6" or greater snowstorm in the Middle Atlantic and southern New England regions remains above the climatological probability, but that probability has decreased, namely due to reduced AO blocking. My preference for the days 3-5 period is the 0z ECMWF and for days 6-10 is a blend of the 0z EPS and 0z GEFS.

Finally, the guidance continues to indicate that the EPO will likely go positive and the AO could go strongly positive late in the first week in January. The result should be a retreat of the cold and a pause in snowfall opportunities in the Middle Atlantic region and possibly at least southern New England. Based on the experience of the current winter to date and an evolving La Niña event similar to that of winter 2000-01, my operating assumption remains that such a pattern shift will likely be temporary. In sum, winter 2017-18 is far from finished.