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December 2020 General Discussions & Observations Thread


bluewave
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1 minute ago, CPcantmeasuresnow said:

There have been 33 Decembers with 10 or more inches of snow in NYC

27 of those winters have then had 30 or more inches for the season or 81.8%

20 of the 33 have had 40 or more inches of snow for the season or 60.6%

12 of the 33 have had 50 or more inches of snow or the season or 36.3%

I like those odds.

I hope we can get one more event to get over the top- reaching 12 inches for the month would be nice.

 

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Revision of first post

There have been 29 Decembers with 10 or more inches of snow in NYC

24 of those winters have then had 30 or more inches for the season or 82.8%

17 of the 29 have had 40 or more inches of snow for the season or 58.6%

9 of the 29 have had 50 or more inches of snow or the season or 31.0%

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I measured 7" on the ground on Riverside Drive this morning, so glad to hear CPK reported 10"

Anyone lamenting the fact that we didn't reach the high end potential has to go outside and absorb the fact that we have - at least here in the city - 7-10" of powdery snow blowing and drifting a week before Christmas. It is spectacular outside.

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9 minutes ago, uncle W said:

this is the anniversary of the great ice storm of 1973...one of the analogs out for this year...

While we have surpassed many previous snowfall records since 1994, that winter really stands as the last widespread severe ice storm. I had an ice storm in Long Beach on Valentine’s Day 2007 and Feb 2, 2011. But neither one of those were on par with Jan 1994. Jan 94 was my only ice storm in Long Beach lasting over 12 hours. It was remarkable how even Long Beach was able to stay in the 20s with freezing rain from the early morning into the night.

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1 minute ago, bluewave said:

While we have surpassed many previous snowfall records since 1994, that winter really stands as the last widespread severe ice storm. I had an ice storm in Long Beach on Valentine’s Day 2007 and Feb 2, 2011. But neither one of those were on par with Jan 1994. Jan 94 was my only ice storm in Long Beach lasting over 12 hours. It was remarkable how even Long Beach was able to stay in the 20s with freezing rain from the early morning into the night.

that was the BECS of ice storms and so beautiful at the end...KPOU at one point was 3 degrees with "heavy freezing rain"  WTF was going on lol

We were below freezing for the entire event here.

 

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14 minutes ago, bluewave said:

While we have surpassed many previous snowfall records since 1994, that winter really stands as the last widespread severe ice storm. I had an ice storm in Long Beach on Valentine’s Day 2007 and Feb 2, 2011. But neither one of those were on par with Jan 1994. Jan 94 was my only ice storm in Long Beach lasting over 12 hours. It was remarkable how even Long Beach was able to stay in the 20s with freezing rain from the early morning into the night.

there were three ice storms that month...the 7-8th storm was all below freezing for me...

 

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3 hours ago, LibertyBell said:

yes see this proves my point that ENSO is not as useful of a predictor as AO/NAO are.  The La Nina is still there of course, but it is not influencing our weather as much as AO/NAO are.

 

You may be right... I don't know.  What I do know is that anything  beyond two weeks with reliability is not easy and I myself, while I look to our long rangers for hope (or lack of), I don't think we yet have a good handle on the multiple influences that carve out a season.  So, I'll continue to pay attention but I'm not confident of anything beyond 11 days. 

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45 minutes ago, bluewave said:

While we have surpassed many previous snowfall records since 1994, that winter really stands as the last widespread severe ice storm. I had an ice storm in Long Beach on Valentine’s Day 2007 and Feb 2, 2011. But neither one of those were on par with Jan 1994. Jan 94 was my only ice storm in Long Beach lasting over 12 hours. It was remarkable how even Long Beach was able to stay in the 20s with freezing rain from the early morning into the night.

Was crazy up here too in Jan 94 -there was one, not sure which but it jumped into the 40's briefly then flash froze down to 0.   Roads were a mess for days

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5 hours ago, EastonSN+ said:

GEFS and GEPS look solid throughout. Only have EPS to day 10 looks good. 

In other board they said EPs looses ao and NAO end of month. Hopefully a reload or switch to -epo to offset?

not saying this is another 10-11 winter, but in that winter we had a big warm up after Boxing day and then by the 10th of Jan we were back in business....

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5 minutes ago, Brian5671 said:

not saying this is another 10-11 winter, but in that winter we had a big warm up after Boxing day and then by the 10th of Jan we were back in business....

By the tail end of January the high latitude blocking just completely fell apart, vanished and it never came back again, right through April. Had it stayed, that winter would have easily surpassed 95-96 

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1 minute ago, snowman19 said:

By the tail end of January the high latitude blocking just completely fell apart, vanished and it never came back again, right through April. Had it stayed, that year would have easily surpassed 95-96 

We did luck out with warm and dry after that-a bunch of cutters with 40-50 inches of snow on the ground would have been a disaster

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8 minutes ago, snowman19 said:

By the tail end of January the high latitude blocking just completely fell apart, vanished and it never came back again, right through April. Had it stayed, that winter would have easily surpassed 95-96 

I had 60 inches by February 1st.

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18 hours ago, donsutherland1 said:

A major snowstorm is now blanketing much of the region. By the time the snow ends tomorrow, much of central Pennsylvania to New England will have picked up a foot or more of snow.

Estimated total snowfall amounts include:

Allentown: 12"-18"
Boston: 8"-16"
Bridgeport: 8"-16"
Hartford: 12"-18"
Islip: 5"-10"
New York City: 7"-14"
Newark: 7"-14"
Philadelphia: 4"-8"
Poughkeepsie: 12"-18"
Providence: 6"-12"

Some areas could see 20" or above snowfall amounts.

Since 2010, the three biggest December snowstorms for Boston, New York City, and Philadelphia were:

Boston:
18.2", December 25-27, 2010
7.1", December 1-3, 2019
6.4", December 17, 2013

New York City:
20.0", December 25-27, 2010
5.0", December 14-15, 2013
4.6", December 9-10, 2017

Philadelphia:
12.4", December 25-27, 2010
8.6", December 8, 2013
4.1", December 9-10, 2017

During the December 10-31, 1950-2019 period, an AO- was the most important teleconnection for a significant Middle Atlantic (6" or more) snowstorm. Since 1950, the following percentage of 6" or greater snowstorms occurred when the AO was negative: Boston: 50%; New York City: 75%; and, Philadelphia: 88%. There were 8 snowstorms that brought 6" or more snow to at least two of the following cities: Boston, New York City, and Philadelphia. 7/8 (88%) occurred when the AO was negative. All storms from the subset from these 8 storms where 10" or more snow fell in at least one of those cities occurred with a negative AO. The most common synoptic pattern when at least two of the aforementioned cities picked up 6" or more snow (63%) was an AO-/PNA+ combination. The most recent such storm was the December 25-27, 2010 "Boxing Day Blizzard."

With the persistence of Arctic blocking, uncertainty about the closing days of December has increased. At present, the guidance has backed off somewhat from the warmth that had been shown previously.

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 probability of December's having a 40.0° or above mean temperature has fallen sharply with the development of strong AO blocking.  

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 +28.65.

Today, the preliminary Arctic Oscillation (AO) figure was -3.009. That is the lowest AO value since February 1, 2019 when the AO was -3.315.

On December 15 the MJO was in Phase 5 at an amplitude of 0.868 (RMM). The December 14-adjusted amplitude was 1.070.

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.

Based on sensitivity analysis applied to the latest guidance, there is an implied 56% probability that New York City will have a warmer than normal December. December will likely finish with a mean temperature near 38.4°.

 

Don - I think you may want to reconsider your prediction of "likely below normal snowfall" as far as I can see only 2 times since the beginning of record keeping at Central Park when they recorded at least 10 inches of snow in December they had below normal seasonal snowfall - most of the time when they had  at least 10 inches of snow in December they recorded above normal snowfall for the season with some years around normal.............

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There have been 29 Decembers with 10 or more inches of snow in NYC, but stupidly this morning I included this year being the 29th December with 10 inches or more in the calculations below.

So there have been 28 full seasons in NYC with 10 or more inches of snow in December and here's how they fared. I'm sure most don't care but I do strive for accuracy, so here's the corrected percentages.

24 of those winters have then had 30 or more inches for the season or 85.7%

17 of the 28 have had 40 or more inches of snow for the season or 60.7%

9 of the 28 have had 50 or more inches of snow for the season or 32.1%

4 of the 28 have had 60 or more inches of snow for the season or 14.2%

1 of the 28 have had 70 or more inches of snow for the season or 3.6%

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Someone may have already posted this but the 1:00pm update in Central Park was 10.5 inches for the storm.
 
The city now needs only  0.8 inches by the end of the month to reach a 30 inch average, when the new 30 year averages are calculated next month.

Amazing when it looked like that was a lock 2 and half years ago and it's coming right down to the wire.
 
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44 minutes ago, MJO812 said:

Not bad for 180 hours out.

 

The big blocking high that quickly developed over the Arctic in the 6-10 day forecast period closed the deal.  But the EPS did a good job forecasting the overall pattern. One of the better EPS performances from late November into December. 

 

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