December 2020 General Discussions & Observations Thread

[MJO812]

First model up tonight is the Icon with suppression.

[qg_omega]

2 hours ago, donsutherland1 said:

New York City received its first snowfall of winter 2020-21 today. However, it was not measurable. Just a trace of snow was reported.

Through today, the preliminary AO average for December is -0.949. On 75% of days, the AO has been negative, including 63% when the AO has been -1.000 or below. Nevertheless, a warm anomaly has prevailed during the first eight days of December. Moreover, December remains likely to finish with a warm anomaly.

Such situations are not common. December 2001 was one such case. The AO was negative on all 31 days and at or below -1.000 on 53% of days. The AO averaged -1.276 with a minimum value of -3.293 on December 28. At New York City, the monthly mean temperature was 44.1° (then the warmest December on record, which was eclipsed in 2015) and only a trace of snow was recorded.

Tomorrow will likely remain cooler than normal. Some snow flurries and snow showers are likely. Some parts of the region could pick up a coating of snow. Afterward, milder air will move into the region. Somewhat cooler air could return to the region after next weekend.

A sustained warmer pattern could begin to develop toward the winter solstice. The closing 10 days of December could wind up generally warmer than normal. The EPS weeklies and new subseasonal guidance are in strong agreement that the last week of December will likely be warmer than normal. The latest CFSv2 weekly guidance favors much warmer than normal readings.

Historic experience following exceptionally warm November cases suggests that a warmer than normal December remains the base case. Almost 90% of cases with a November mean temperature of 51.5° or above in Central Park (2020 saw the temperature average a record 52.9° in November) went on to record a warmer than normal December and just over three-quarters of such cases saw December register a monthly mean temperature of 40.0° or above.

The ENSO Region 1+2 anomaly was -0.5°C and the Region 3.4 anomaly was -1.1°C for the week centered around December 2. For the past six weeks, the ENSO Region 1+2 anomaly has averaged -0.77°C and the ENSO Region 3.4 anomaly has averaged -1.35°C. La Niña conditions will likely prevail at least through the winter.

The SOI was +7.73.

Today, the preliminary Arctic Oscillation (AO) figure was -1.261.

On December 7 the MJO was in Phase 4 at an amplitude of 0.677 (RMM). The December 6-adjusted amplitude was 0.784.

Based on the latest guidance, no significant stratospheric warming event is likely through the first two weeks of December. The warming above 3 mb in response to recent strong Wave 1 activity could abate toward or just after mid-month.

Since 1950, there have been five cases where a La Niña developed during June-July-August or afterward following an El Niño winter. 4/5 (80%) of those cases saw a predominant EPO+/AO+ winter pattern. The most recent such case was 2016-17. 10/11 (91%) of the La Niña winters that followed an El Niño winter featured a predominantly positive EPO. A predominant EPO+/AO+ pattern is very likely for winter 2020-21. It is likely that the Middle Atlantic and southern New England areas will see a warmer than normal winter with below normal snowfall.

Based on sensitivity analysis applied to the latest guidance, there is an implied 73% probability that New York City will have a warmer than normal December. December will likely finish with a mean temperature near 40.0°.

 

There was a trace of snow today?

[psv88]

26 minutes ago, qg_omega said:

There was a trace of snow today?

coastal areas saw flurries

[donsutherland1]

33 minutes ago, qg_omega said:

There was a trace of snow today?

There were flurries in parts of the area, including Central Park.

[Allsnow]

All 3 ensembles now have textbook Greenland blocking developing 

[CIK62]

The next 8 days are averaging 43degs.(38/47).       Making it 38degs., or +1.0.

GFS has aTrace of snow today and that is it.

CMC, EURO have action around mid-month.

GFS heads for 70* near Christmas.

GEFS: The only 5-Day period that is even near Normal is centered on the 18th.

35*(65%RH) here at 6am, thin overcast.     (It was 33* near midnight).        36* at 9am.       38* by Noon.

[MJO812]

1 hour ago, Allsnow said:

All 3 ensembles now have textbook Greenland blocking developing 

SSW doing its magic ?

[MJO812]

8 minutes ago, bluewave said:

Yeah, December 1996 style. Greenland blocking linking up with a piece of the Western Atlantic Ridge. Notice the unfavorable Pacific maintaining a mild Pacific airmass across much of the US. 

 

AO looks really good on the ensembles. We just have to flip the epo.

[donsutherland1]

Morning thoughts...

Today will be variably cloudy. Some snow flurries and snow showers are possible. A rain shower is also possible during the afternoon. Some parts of the region could pick up a coating of snow. Temperatures will likely top out in the upper 30s and lower 40s in most of the region. Likely high temperatures around the region include:

New York City (Central Park): 38°

Newark: 41°

Philadelphia: 42°

Milder air will return tomorrow and prevail through the remainder of the week.

[MJO812]

Radar looks nice west of the coast

Too bad the mountains will break apart the snow wall.

[MJO812]

11 minutes ago, bluewave said:

That won’t happen anytime soon with the Pacific firehose Pacific Jet and MJO stalled in phase 4-5

 

There will be a few chances of snow coming up if the blocking actually exists.

[White Gorilla]

53 minutes ago, MJO812 said:

There will be a few chances of snow coming up if the blocking actually exists.

Oops snow.... 

[psv88]

20.1 this morning, coldest morning of the fall so far, heavy frost 

[Tatamy]

51 minutes ago, MJO812 said:

Radar looks nice west of the coast

Too bad the mountains will break apart the snow wall.

A lot of that precip is not reaching the ground- even in the higher elevations.  

[MJO812]

9 minutes ago, psv88 said:

20.1 this morning, coldest morning of the fall so far, heavy frost 

20 degrees in Long Island ?

36 here 

[psv88]

2 minutes ago, MJO812 said:

20 degrees in Long Island ?

36 here 

Yes.

Islip was 21

westhampton was 14

[MJO812]

4 minutes ago, psv88 said:

Yes.

Islip was 21

westhampton was 14

Wow

[EastonSN+]

1 hour ago, bluewave said:

That won’t happen anytime soon with the Pacific firehose Pacific Jet and MJO stalled in phase 4-5

 

Does it help that it's low amplification? Wonder if it had similar amplification in 1996.

[qg_omega]

9 hours ago, donsutherland1 said:

There were flurries in parts of the area, including Central Park.

I don't see it Don:

 

[crossbowftw3]

It's definitely coming down in the Catskills. A dusting/coating on most everything, even the roads. Maybe I can sneak 1-2"? Would be surprised if more than 1" fell though.

[the_other_guy]

31F Frosty run this morning! Feels like snow 

[Brian5671]

Last few days have actually felt like winter here with lows in the low 20's and frost everywhere each morning.

[MJO812]

37 minutes ago, qg_omega said:

I don't see it Don:

 

Yesterday  there were flurries in NYC

[MJO812]

5 minutes ago, JoshSnow said:

nice snow showers coming up. Suburbs can get a nice dusting with this. I’ll be front I thought it was going to be virga but this is good snow showers coming up

Majority of that will be eaten by the mountains

[IrishRob17]

3 minutes ago, JoshSnow said:

nice snow showers coming up. Suburbs can get a nice dusting with this. I’ll be front I thought it was going to be virga but this is good snow showers coming up

That’s quite the ringer volume you have set there but I digress...just some virga in my yard so far, hoping to get some flakes at some point as the heavier echoes move through. 

[jm1220]

35 minutes ago, MJO812 said:

Majority of that will be eaten by the mountains

Temps are also getting into the mid-upper 30s now so it may be mix rain/snow when it does hit the ground. 

[Allsnow]

1 hour ago, bluewave said:

The RMM charts don’t seem to be reflecting the actual strength of the forcing over the Maritime Continent. Notice how robust the VP anomalies are compared to the RMM charts. This is probably related to the La Niña which also produces forcing over the Maritime Continent. The 500 mb composite  favors a mild +EPO pattern.

Looks like some p7 at the end of the month could improve the pac. 

[SnoSki14]

Bluewave always with the accurate response to rain on the weenie parade.

Pacific puke looks to dominate rest of the month. We'd have to be lucky to score with such a putrid airmass over us.

Odds would improve in January.

[Allsnow]

3 hours ago, bluewave said:

Yeah, December 1996 style. Greenland blocking linking up with a piece of the Western Atlantic Ridge. Notice the unfavorable Pacific maintaining a mild Pacific airmass across much of the US. 

 

Southeast ridge is non existent which is not normal for Niña 

[Eduardo]

4 minutes ago, SnoSki14 said:

Bluewave always with the accurate response to rain on the weenie parade.

Pacific puke looks to dominate rest of the month. We'd have to be lucky to score with such a putrid airmass over us.

Odds would improve in January.

Minimal improvement on the PAC side can put us in the game as long as the ATL side cooperates.  Even a decent WPO can inject some arctic air for the NAO to hold in place.  Need to tamp that PAC jet down just a bit though.  It's been a killer these past few years.