December 2020 General Discussions & Observations Thread

[LibertyBell]

20 hours ago, donsutherland1 said:

To date, the Arctic Oscillation (AO) has averaged -1.678 this month. It has been negative on 89% of days. It has been -1.000 or below 78% of the time and -2.000 or below on 39% of the days. A negative AO has been present in more than three-quarters of cases where Philadelphia and New York City saw 6" or greater snowstorms during the December 10-31 period, one of which occurred during December 16-17.

Since 2000, December snowfall exceeded 6" or more in 5/7 (71%) of cases in both New York City and Philadelphia when the AO averaged -1.000 or below in December. In Philadelphia, seasonal snowfall exceeded 20" or more in 80% of those December cases when 6" or more snow fell and 30" or more in 60% of those cases. In New York City, seasonal snowfall exceeded 30" or more in all those December cases with 6" or more snowfall and 40" or more in 80% of those cases. The recent snowstorm during what has been a blocky December suggests that seasonal snowfall prospects have increased especially from north of Philadelphia into southern New England. Nevertheless, there remains a chance that the current La Niña could adversely influence the pattern leading to a disappearance of the blocking. Were blocking to disappear, snowfall prospects would diminish. For now, blocking appears likely to continue into the start of January.

Temperatures will slowly moderate this weekend. Tomorrow will be fair and still cool. Sunday will be variably cloudy with some rain and snow showers possible. A strong storm could pass to the west of the region after midweek.

With the persistence of Arctic blocking, uncertainty about the closing days of December has increased. A possible piece of an Arctic air mass could even push into parts of the region on or just after December 25.

Frigid Arctic air is currently centered in northwestern Canada. Earlier today, near record and record cold was reported in parts of the Northwest Territories. At Norman Wells, the temperature fell to -53° (old record: -50°, 1961). At Yellowknife, the temperature fell to a near-record -48°.

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. Sustained Arctic blocking will produce a much cooler outcome. The monthly temperature anomaly could wind up only somewhat above normal.  

The ENSO Region 1+2 anomaly was -0.1°C and the Region 3.4 anomaly was -1.2°C for the week centered around December 9. For the past six weeks, the ENSO Region 1+2 anomaly has averaged -0.62°C and the ENSO Region 3.4 anomaly has averaged -1.43°C. La Niña conditions will likely prevail at least through the winter.

The SOI was +34.10.  

Today, the preliminary Arctic Oscillation (AO) figure was -2.035.

On December 17 the MJO was in Phase 5 at an amplitude of 0.790 (RMM). The December 16-adjusted amplitude was 0.845.

Based on the latest guidance, no significant stratospheric warming event is into the final week of December.

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. The large snowfall that just took place provides a strong contrary signal to the below normal snowfall idea. Should blocking continue, the probability of above normal snowfall would likely increase.

Based on sensitivity analysis applied to the latest guidance, there is an implied 54% probability that New York City will have a warmer than normal December. December will likely finish with a mean temperature near 38.0°.

 

 

Don I wanted to ask you about this:

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. 

 

Aren't la ninas after el ninos supposed to be exceptionally snowy?  Two cases in point are 1995-96 and 2010-11

 

[LibertyBell]

3 minutes ago, bluewave said:

The Christmas storm looks to really create a major wave breaking event. So I am taking a wait and see approach as to how long after that we can expect a colder and snowier storm track. I am hoping that we can finally get a cold enough storm for the South Shore to finally get into the jackpot zone like we were in 15-16, 16-17, and 17-18.

and it's probably better for us if it happens in January, all of the ones you mentioned happened in January I believe.

 

[LibertyBell]

6 hours ago, bluewave said:

These are two great tweets on how the record warm SSTs to our east are providing extra moisture to snowstorms. But on the flip side, we also get bigger rain and wind storms when the intense lows track to our west. Especially with systems that can go negative tilt.
 

 

wait shouldn't this also include the Jan 2013 and 2016 storms, it's not just about the interior, it's happening all over the east....

[donsutherland1]

2 minutes ago, LibertyBell said:

Don I wanted to ask you about this:

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. 

 

Aren't la ninas after el ninos supposed to be exceptionally snowy?  Two cases in point are 1995-96 and 2010-11

 

Those La Niña events developed prior to June-July-August. In any case, the widespread warm SSTAs over the Pacific, the IOD, and AO- have laid the basis for a different outcome this winter. Things are now leaning decidedly toward a snowier outcome in the northern Middle Atlantic region into New England. Unless the AO blocking is sustained, it’s too soon to be confident about snowfall totals from Baltimore and southward.

[LibertyBell]

2 minutes ago, donsutherland1 said:

Those La Niña events developed prior to June-July-August. In any case, the widespread warm SSTAs over the Pacific, the IOD, and AO- have laid the basis for a different outcome this winter. Things are now leaning decidedly toward a snowier outcome in the northern Middle Atlantic region into New England. Unless the AO blocking is sustained, it’s too soon to be confident about snowfall totals from Baltimore and southward.

Don what do you think of this talk of the la nina going away early this season?  Is there any basis for this?

 

[MJO812]

1 hour ago, IrishRob17 said:

Um

Euro has 57 here Christmas morning...prefer I say the Christmas morning shorts?

 

1 hour ago, Stormlover74 said:

Euro is very delayed with the cold air 

Gfs has the cold front already past us on Christmas  morning 

[MJO812]

5 hours ago, wdrag said:

Am on the cusp of a minor snow topic for 1-3" of snow NYC combined events Sunday and Tuesday.  Will review at 3P. If RGEM/GGEM NOT on board then probably, no topic. 

18z nam

[bluewave]

10 minutes ago, LibertyBell said:

and it's probably better for us if it happens in January, all of the ones you mentioned happened in January I believe.

 

I only got 4” here before the sleet arrived. So the bar is set pretty low. I will go out on a limb say that there will be a better storm than that at some point this winter.

[LibertyBell]

4 minutes ago, bluewave said:

I only got 4” here before the sleet arrived. So the bar is set pretty low. I will go out on a limb say that there will be a better storm than that at some point this winter.

I was somewhat surprised to see that JM in Huntington only got 8"- about the same amount I got in the western part of the south shore.

 

[WeatherFox]

For reference, historical and educational purposes this NOAA  product was put out two months ago:  https://www.noaa.gov/media-release/us-winter-outlook-cooler-north-warmer-south-with-ongoing-la-nina

[donsutherland1]

14 minutes ago, LibertyBell said:

Don what do you think of this talk of the la nina going away early this season?  Is there any basis for this?

 

There is model consensus for weakening. But it’s premature to assume that it dissipates entirely in the near-term. On Monday, we’ll get the latest weekly numbers to see where things stood for the week centered around December 16.

[bluewave]

12 minutes ago, LibertyBell said:

I was somewhat surprised to see that JM in Huntington only got 8"- about the same amount I got in the western part of the south shore.

 

The WAA aloft and dryslot did their thing.

 

[qg_omega]

5 minutes ago, bluewave said:

The WAA aloft and dryslot did their thing.

 

Not great post by upton, my parents in Howard beach on the water got more snow than me 30 miles due north in white plains.  They just picked a bad measurement

[Isotherm]

My brief thoughts on the coming multi-week period (reposted in my outlook thread as well main board); rapidly increased favorability should initiate at the tail end of December.

"The GFS based guidance is likely rushing the genesis/realization of the auspicious pattern; the ECMWF/EPS are more congruous with the physical drivers. z50 geopotential heights favor a positive NAO from now through circa Dec 28th; as the Canadian 'warming' occurs in the stratosphere and z50 restructures w/ a wave-2 paradigm, geopotential heights will begin to respond within a few days over the NAO domain, with diminution there in the final 1-2 days of December/beyond. The classical Siberian high descent initiates December 26th +/- a couple of days which will induce a +EAMT and jet extension event at the very end of December, and thus ameliorating the downstream Pacific/PNA/EPO domain pattern by the early days of January. Therefore, the December 28th-January 2nd period should feature expeditious amelioration of the hemispheric pattern, first, with improvement in the NAO domain at the very end of December, then, shortly followed by the Pacific. If there is a storm threat of significance in late December, it would likely favor the interior Northeast/New England, in my view, with a threat for I-95 beyond that time-frame (sometime in the first 10 days of January), but we'll see how it evolves."

[Allsnow]

Models have .5 to inch of snow tomorrow for the area 

[SnoSki14]

2 minutes ago, Allsnow said:

Models have .5 to inch of snow tomorrow for the area 

Nam has another inch or so in a few days.

[Allsnow]

The last two days have not gotten above 32 in nyc. The last time this happen was March 2019 

[bluewave]

1 hour ago, LibertyBell said:

wait shouldn't this also include the Jan 2013 and 2016 storms, it's not just about the interior, it's happening all over the east....

I guess that he only ran the model for that storm. But it’s also happening in places like Japan.

https://www.washingtonpost.com/weather/2020/12/18/japan-snow-stranded-motorists/

 

[nycsnow]

2 hours ago, LibertyBell said:

 

whats the time frame for these high gusts?

Christmas eve (night)? or during the day or what and how long are they forecast to last?

Timing is different on models so far but Xmas Eve afternoon through the night give or take 

[nycsnow]

Gfs has hours and hours of winds 50+ with a peak of gust to 70s

[the_other_guy]

1 hour ago, qg_omega said:

Not great post by upton, my parents in Howard beach on the water got more snow than me 30 miles due north in white plains.  They just picked a bad measurement

Absolutely. Queens and Manhattan have way more snow than Westchester per my own eyes.

But we will get the last laugh...we melt a lot slower haha

[donsutherland1]

To date, New York City's Central Park has had a monthly temperature anomaly of 0.1° below normal. However, the month will swing back to positive departures in coming days as slow moderation continues.

Tomorrow will be variably cloudy with some rain and snow showers possible. A strong storm could pass to the west of the region after midweek bringing a period of moderate to heavy rain, high winds, and unseasonably warm temperatures before colder air returns afterward.

Parts of western Canada again experienced record cold. At Norman Wells, Northwest Territories, where the temperature plunged to a record -54° yesterday, the temperature fell to -52° today. That broke the daily record of -50°, which was set in 1956.

With the persistence of Arctic blocking, uncertainty about the closing days of December has increased. A possible piece of an Arctic air mass could even push into parts of the region on or just after December 25.

The ENSO Region 1+2 anomaly was -0.1°C and the Region 3.4 anomaly was -1.2°C for the week centered around December 9. For the past six weeks, the ENSO Region 1+2 anomaly has averaged -0.62°C and the ENSO Region 3.4 anomaly has averaged -1.43°C. La Niña conditions will likely prevail at least through the winter.

The SOI was +30.57 today. That is the 3rd consecutive day on which the SOI was +30.00 or above. The last time that happened was January 24-26, 2012.

Today, the preliminary Arctic Oscillation (AO) figure was -1.506.

On December 18 the MJO was in Phase 5 at an amplitude of 0.869 (RMM). The December 17-adjusted amplitude was 0.785.

Based on the latest guidance, no significant stratospheric warming event is into the final week of December.

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. The large snowfall that just took place provides a strong contrary signal to the below normal snowfall idea. Should blocking continue, the probability of above normal snowfall would likely increase.

The recent snowstorm during what has been a blocky December suggests that seasonal snowfall prospects have increased especially from north of Philadelphia into southern New England. At New York City, there is a high probability based on historic cases that an additional 20" or more snow will accumulate after December. Were blocking to disappear, snowfall prospects would diminish. For now, blocking appears likely to continue into the start of January.

Based on sensitivity analysis applied to the latest guidance, there is an implied 53% probability that New York City will have a warmer than normal December. December will likely finish with a mean temperature near 37.9°.

 

[LibertyBell]

4 hours ago, bluewave said:

The WAA aloft and dryslot did their thing.

 

I heard some in the media mention that the megaband up near Binghamton robbed N NJ and the LHV of moisture and that's why they got dryslotted in the early evening hours

[LibertyBell]

3 hours ago, nycsnow said:

Gfs has hours and hours of winds 50+ with a peak of gust to 70s

whats the time frame for this?

 

[LibertyBell]

3 hours ago, nycsnow said:

Timing is different on models so far but Xmas Eve afternoon through the night give or take 

oh nvmd just saw it....having a power outage Xmas Eve night would SUCK.

[MJO812]

Snow showers on the Nam tomorrow for NYC west

[wdrag]

5 hours ago, MJO812 said:

18z nam

Holding off til 530A Sunday, to be more certain it will be worthwhile. Looking halfway decent for bit of new snow NYCby Noon Tuesday. 

[LibertyBell]

4 hours ago, Isotherm said:

My brief thoughts on the coming multi-week period (reposted in my outlook thread as well main board); rapidly increased favorability should initiate at the tail end of December.

"The GFS based guidance is likely rushing the genesis/realization of the auspicious pattern; the ECMWF/EPS are more congruous with the physical drivers. z50 geopotential heights favor a positive NAO from now through circa Dec 28th; as the Canadian 'warming' occurs in the stratosphere and z50 restructures w/ a wave-2 paradigm, geopotential heights will begin to respond within a few days over the NAO domain, with diminution there in the final 1-2 days of December/beyond. The classical Siberian high descent initiates December 26th +/- a couple of days which will induce a +EAMT and jet extension event at the very end of December, and thus ameliorating the downstream Pacific/PNA/EPO domain pattern by the early days of January. Therefore, the December 28th-January 2nd period should feature expeditious amelioration of the hemispheric pattern, first, with improvement in the NAO domain at the very end of December, then, shortly followed by the Pacific. If there is a storm threat of significance in late December, it would likely favor the interior Northeast/New England, in my view, with a threat for I-95 beyond that time-frame (sometime in the first 10 days of January), but we'll see how it evolves."

Yes thats what I was thinking also....first an interior threat at the end of Jan and then -maybe- a BIG storm for the coast sometime between Jan 5 and the 10th.  Notice now we're all thinking of 95-96 lol.

[LibertyBell]

4 hours ago, qg_omega said:

Not great post by upton, my parents in Howard beach on the water got more snow than me 30 miles due north in white plains.  They just picked a bad measurement

well the measurement was a good representation, JFK measured 7.2 and Marine Park had 7.5 and I'm 4 miles east of JFK and had close to 8 here.

[uncle W]

3 minutes ago, LibertyBell said:

I heard some in the media mention that the megaband up near Binghamton robbed N NJ and the LHV of moisture and that's why they got dryslotted in the early evening hours

the Dec 21-22, 1959 storm had 6-15" in the city...6" at Battery Park and 15" in the Bronx...13.7" in Central Park...8" in Brooklyn...