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December 2020 General Discussions & Observations Thread


bluewave
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10 hours ago, bluewave said:

Yeah, the Pacific Jet will continue to dominate into late December. It will be interesting to see if the SSW verifies. If it does, then we’ll have to wait and see if it benefits Eurasia or North America.

 

 

SSW is the biggest single event that can change a pattern, there's usually a 2-4 week delay between the event and the change, right Chris?

 

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11 hours ago, bluewave said:

First December for NYC with 10”+ of snow and a 60°Christmas. It was also the first 7 year period with 3 years reaching 60° or warmer on Christmas. 

 

Data for December 25 - NY CITY CENTRAL PARK, NY
Click column heading to sort ascending, click again to sort descending.
Date
Max Temperature 
Min Temperature 
Precipitation 
Dec Snowfall 
 
2015-12-25 66 57 0.01 T  
1982-12-25 64 41 0.02 3.0  
1889-12-25 64 43 0.00 6.0  
2014-12-25 62 44 0.09 1.0  
1940-12-25 62 38 0.00 3.0  
1979-12-25 61 50 0.87 3.5  
2020-12-25 61     10.5  
1964-12-25 60 49 T 3.1  

 

Yeah this is normal now lol.

The warmth more than the 10" pre solstice snowfall....

 

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5 hours ago, Allsnow said:

The pac is going to be a issue until the +EAMT retracts. I see no reason why we won’t snow again in nyc. How many people thought we would get 10+ in nyc for December? The next shot will probably be between January 2-5th. The eps likes those dates as of now. I see no reason to fear a repeat of winter 2020! This is not last winter by any means. 

right that is the period I'm looking at also.  Anyone who thought we would have another snowstorm in December was foolish.  That's not how our climatology works.  The period I've been looking at is a little later than yours though, between the 5th and the 10th. Panic is for the weak-minded.

 

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3 hours ago, nycwinter said:

2 memorable storms in december that is 2 better then we had last winter i will take it..

well only one of them was snow lol.  Some of my friends are already sick and tired of winter and want spring to come already....I was told dont tell me what the weather is going to be unless it's going to be above 50 degrees and sunny every day!

 

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Very slow mover on gfs. Blocking can do wonders. 
Models keep signaling a storm during the 1st week of January.
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5fe66bbe9e2e9.png.8618fa991c68b097ef4f1bb339abbfd3.png

One thing I’ve learned from my many, many years of watching winter weather is this... you can’t trust the long range details in the models, just the framework. e.g., it indicates we’re going to walk into a room soon and that room will be a kitchen, so you assume there will be a refrigerator, dishwasher, and microwave, but we have no idea what brand and wattage they’ll be until we’re in the next room over and can peer in through the doorway.

tl;dr, it sounds like we’re going to have a storm in about ten days, and we’re not sure yet what it will bring, but something is there and it’s going to change a lot in the coming days.


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Colder air around the backside of the storm that brought damaging winds, heavy rain, and mild temperatures has now overspread the region. Tomorrow will be fair but unseasonably cold.

As a strong storm pushed northward, unseasonably warm air covered parts of the Northeast and eastern Canada. Record high temperatures included:

Bangor: 61° (old record: 54°, 2014 and 2015) ***Highest Temperature for 2nd Half of December***
Burlington: 65° (old record: 62°, 1964)
Cap Chat, QC: 61° (old record: 44°, 2015)
Caribou: 57° (old record: 54°, 2003 and 2014) ***Highest Temperature for 2nd Half of December***
Charlottetown, PE: 56° (old record: 54°, 1996)
Fredericton, NB: 63° (old record: 54°, 2003) ***Highest Temperature for 2nd Half of December***
Gaspé, QC: 54° (old record: 51°, 2003)
Goose Bay, NL: 46° (old record: 45°, 1964)
Halifax: 56° (tied record set in 1996)
Montreal: 56° (old record: 53°, 1964)
Poughkeepsie: 65° (old record: 63°, 1964)
Quebec City: 48° (old record: 43°, 2015)
Rivière-du-Loup, QC: 55° (old record: 42°, 2015)
Saint John, NB: 59° (old record: 55°, 2003)
Yarmouth, NS: 58° (old record: 55°, 2003)

In parts of eastern Canada, record temperatures remain likely into Sunday. Meanwhile, unseasonably cold air will push into Florida. Record low temperatures are possible in some parts of the state, especially along the Gulf Coast and southern portions of the Florida Peninsula tomorrow morning.

The likely continuation of Arctic blocking through at least the first 10 days of January will provide a higher than climatological probability for above normal snowfall with the focus on the January 1-10 period. There is modest clustering of support among the EPS ensemble members for January 3-5. The AO- is particularly important for moderate or significant snowfalls in the New York City and Philadelphia areas.

For the December 15-January 15, 1950-2020 period, the following percentages of select snowstorms have occurred when the AO was negative:

New York City:
4" or more: 66%
6" or more: 80%
10" or more: 86%

Philadelphia:
4" or more: 81%
6" or more: 85%
10" or more: 100%

Further, an AO-/PNA+ pattern is especially favorable for moderate or significant snowstorms during the first half of January. For the January 1-15, 1950-2020 period, daily snowfall reached or exceeded 4" on 1.7% of days in New York City and 1.2% of days in Philadelphia. During AO-/PNA+ patterns, those respective frequencies were 2.3% and 1.7%. In short, moderate or significant snowfalls were 37% more common in New York City and 42% more common in Philadelphia during AO-/PNA+ patterns.

The ENSO Region 1+2 anomaly was -0.8°C and the Region 3.4 anomaly was -0.9°C for the week centered around December 16. For the past six weeks, the ENSO Region 1+2 anomaly has averaged -0.57°C and the ENSO Region 3.4 anomaly has averaged -1.17°C. La Niña conditions will likely prevail at least through the winter.

The SOI was +4.88 today.

Today, the preliminary Arctic Oscillation (AO) figure was -0.040.

On December 24 the MJO was in Phase 7 at an amplitude of 0.149 (RMM). The December 23-adjusted amplitude was 0.368.

Based on the latest guidance, the probability of a significant stratospheric warming event near or just after the start of January has continued to increase. The highest levels of the stratosphere will warm during the closing days of December. The warming will begin to descend during the opening week of January. In addition, the mean zonal wind at 1 mb will likely reverse while the mean zonal winds at 10 mb and 30 mb slacken considerably.

There is a proverbial fly in the ointment. It appears that this warming event could produce a split in the polar vortex. Typically, when the polar vortex splits, Eurasia is favored for cold. Displacement of the polar vortex often favors North America.

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 95% probability that New York City will have a warmer than normal December. December will likely finish with a mean temperature near 39.0°.

 

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2 hours ago, eduggs said:

If we want to make statistical inferences based on "blocking," I think we have to define the term a lot more precisely. Right now the term is thrown around very unscientifically. It matters a lot how we define it and the specific region we are referring to.

The definition is qualitative, not quantitative. Measures such as the NAO and AO can provide related quantitative information.

https://glossary.ametsoc.org/wiki/Blocking

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The last 6 days of December are averaging 34degs.(24/44).         Making it 30degs., or -3.0. 

Month to date is 40.0[+1.7].           December should end near 38.9[+0.8].

24*(55%RH) here at 6am.     Was 29* at Midnite.         Back to 29* by Noon.        32* by 2pm.        33* by 3pm.        27* by 9pm.

0Z GFS still had Jan.04-05 for 13" this time---but 06Z is already a miss.

NYDay looking awfully like Christmas fiasco.

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Our warm up around the solstice has become the new normal for us. This is the first 10 consecutive years to reach 55° or warmer in NYC. It pushed the NYC December average temperature  so far to 40° and +1.7.
 

Time Series Summary for NY CITY CENTRAL PARK, NY
Click column heading to sort ascending, click again to sort descending.
Ending Date
Highest Max Temperature Dec 18 to Dec 25
Missing Count
2020-12-25 61 0
2019-12-25 57 0
2018-12-25 61 0
2017-12-25 55 0
2016-12-25 58 0
2015-12-25 72 0
2014-12-25 62 0
2013-12-25 71 0
2012-12-25 56 0
2011-12-25 62 0
2010-12-25 40 0
2009-12-25 39 0

 

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1 hour ago, bluewave said:

Our warm up around the solstice has become the new normal for us. This is the first 10 consecutive years to reach 55° or warmer in NYC. It pushed the NYC December average temperature  so far to 40° and +1.7.
 

Time Series Summary for NY CITY CENTRAL PARK, NY
Click column heading to sort ascending, click again to sort descending.
Ending Date
Highest Max Temperature Dec 18 to Dec 25
Missing Count
2020-12-25 61 0
2019-12-25 57 0
2018-12-25 61 0
2017-12-25 55 0
2016-12-25 58 0
2015-12-25 72 0
2014-12-25 62 0
2013-12-25 71 0
2012-12-25 56 0
2011-12-25 62 0
2010-12-25 40 0
2009-12-25 39 0

 

The message always seems to be sent. I wonder when or if it will ever be heard. As always ......

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