December 2020 General Discussions & Observations Thread

[NorthShoreWx]

1 hour ago, STORMANLI said:

7.2" in South Commack

Melted down to

1.34" in the Stratus

1.35" From the Core Sample

That's really close.  I think mine catches very little snow when it's windy.

[NEG NAO]

1 hour 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. 

12Z CMC is further south then 12 Z NAM with precip but doesn't look to be all frozen so IMO this event is not thread worthy YET

[jm1220]

22 minutes ago, NorthShoreWx said:

That's really close.  I think mine catches very little snow when it's windy.

Good thing this snowpack is so water logged. It’ll hang on as long as it can. Irrelevant if this Xmas Eve 70 mph southerly wind event happens I guess lol. 

[nycsnow]

Impressive wind event on most models now

[MJO812]

Gfs keeps enforcing the NAO block.

 

What a great looking pattern 

[NEG NAO]

24 minutes ago, MJO812 said:

Gfs keeps enforcing the NAO block.

 

What a great looking pattern 

need everything to line up next - 50/50 low - strong HP in southern Canada and an active storm track...……….

[HeadInTheClouds]

23 and sunny after a low of 1 below last night. 

[bluewave]

Areas to our north which were below 0° today may experience one of their biggest day 5-6 temperature rises for December. The records for December were set in 2013 and 2008. 

 

 

 

[MJO812]

1 hour ago, NEG NAO said:

need everything to line up next - 50/50 low - strong HP in southern Canada and an active storm track...……….

Agree

[IrishRob17]

1 minute ago, bluewave said:

Areas to our north which were below 0° today may experience one of their biggest day 5-6 temperature rises for December.

 

 

 

Break out the Christmas shorts. 

[bluewave]

4 minutes ago, IrishRob17 said:

Break out the Christmas shorts. 

It’s interesting how persistent this solstice warm up has been especially since 2011. It has occurred under a wide variety of weather patterns. Some years like 2013 had a snowstorm just before the warm up like the forecast for this year. Others like 2017 went into the deep freeze right after Christmas. 2015 featured the historic +13.3 departure and the warmest day of the month was on the 24th.
 

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
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

 

[MJO812]

18 minutes ago, IrishRob17 said:

Break out the Christmas shorts. 

Um

Christmas day will be in the 20s

[IrishRob17]

8 minutes ago, MJO812 said:

Um

Christmas day will be in the 20s

Um

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

[Stormlover74]

19 minutes ago, MJO812 said:

Um

Christmas day will be in the 20s

Euro is very delayed with the cold air 

[LibertyBell]

On 12/18/2020 at 11:51 AM, CPcantmeasuresnow said:

With a seasonal average of 5 inches I guess they're always in a snow drought. LOL

It's almost like saying Atlanta is in a snow drought. When is it a snow drought and when is it just your climate norm.

I still remember Mallow celebrating whenever a La Nina was forecast because he thought Seattle would be getting a ton of snow and the NE would get screwed lol.

 

[LibertyBell]

On 12/18/2020 at 1:47 PM, bluewave said:

Flood potential on the 12z Euro around Christmas. Especially for the interior areas with a 20-40” snowpack. Euro has heavy elevated convection and temperatures into the 50s in those  areas. Maybe we can slowly melt our pack each day so there isn’t a more rapid  melt like they could get north and west of the area if this solution verified.

 

 

 

going back to la nina norms, isn't this a classic situation...la ninas and christmas rapid snowmelt and flooding lol?

 

[LibertyBell]

On 12/18/2020 at 1:52 PM, gravitylover said:

Here it's 4-6* below forecasted highs.

snowcover amount affects both highs and lows

[donsutherland1]

The December 16-17, 2020 snowstorm dumped 10.5" snow on New York City. December cases when 10" or more snow falls have generally seen 20" or more additional snowfall from January to the last snowfall. The historic data suggests that seasonal guidance notwithstanding, the New York City area now has a high probability of seeing 30" or more seasonal snowfall.

January-May Snowfall (1869-2020) following December Monthly Snowfall of 10" or More:

Number of cases by DJF ENSO:
La Niña: 8
Neutral: 13
El Niño: 6
Total: 27

What could result in less snowfall:

1. Collapse of the ongoing La Niña and/or
2. The persistent AO- blocking yields to a sustained AO+ regime

 

[LibertyBell]

On 12/18/2020 at 3:15 PM, MJO812 said:

I'm already looking forward to the next storm.  The pattern looks great. La Nina is dying .

These images are from the Euro. Alot of blocking.

 

What are those three pterodactyl like things flying around on that map lol?

 

[LibertyBell]

23 hours ago, jm1220 said:

Dec is typically when we’d get snowstorms in a Nina so this is evolving the way a Nina should. There’s been more blocking than some predicted which is great, but we have to keep that in place especially since part 2 of Nina winters are usually warm and snowless here. 

according to the other guy the la nina is ending?

 

[bluewave]

4 minutes ago, LibertyBell said:

going back to la nina norms, isn't this a classic situation...la ninas and christmas rapid snowmelt and flooding lol?

 

We can get rapid snowmelt under a variety ENSO conditions. The last one that made local headlines was in March 2015. But I am glad that areas near the coast will have a chance to gradually reduce the snowpack going into the late week storm. 

 

 

[LibertyBell]

1 hour ago, bluewave said:

It’s interesting how persistent this solstice warm up has been especially since 2011. It has occurred under a wide variety of weather patterns. Some years like 2013 had a snowstorm just before the warm up like the forecast for this year. Others like 2017 went into the deep freeze right after Christmas. 2015 featured the historic +13.3 departure and the warmest day of the month was on the 24th.
 

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
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

 

Chris remember Dec 1995 when we had the mid Dec snowstorm and then it got very cold after that and the snowpack persisted through both Christmas and New Years and was even around for the Jan 1996 blizzard?  We got the big melt a week or so after the big blizzard and we even had severe weather in Jan with temps in the mid and upper 60s with lots of flooding and the big Massapequa supermarket roof collapse!

[LibertyBell]

23 hours ago, Brian5671 said:

amazing they always go torch-yes it usually ends up above normal in areas, but the whole country?

in January it might be better to have above normal temps and high noreaster activity, below normal temp Jan usually means a suppressed pattern and it can still snow in Jan with above normal temps- as a matter of fact that might be preferred.

 

[LibertyBell]

22 hours ago, bluewave said:

Yeah, this was our first La Niña with a NYC 6”+ snowstorm in the week before Christmas since 1995. While patterns have changed greatly since then, maybe we could get another shot a major snow event like we did in early January 1996. It may come down to how strong the wave break is with the Christmas storm. The one on December 1st resulted in the record block east of Newfoundland. That blocking eventually shifted poleward and we got our significant snow event this week. Models are going for another big block east of Newfoundland after the Christmas storm. Beyond that time, models may not yet have a handle on how the blocking east of the Maritimes progresses. We can remember how models greatly underestimated the blocking over the North Pole this past week from the day 10-15 period. It suddenly popped up in the 7-9 day forecasts.  So we need to watch for something like that near the end of December. That could potentially set the table for another significant snow event. The animation below is an excellent example of how blocking since early December shifted poleward over time.

https://www.cpc.ncep.noaa.gov/products/intraseasonal/z500_nh_anim.shtml

for the rest of Dec though you dont foresee another big snowstorm correct?  This might be more like 1996 and we watch to Jan- which is fine by me.  The longer we wait the bigger it'll probably be.  Didn't someone say that when you have a 10"+ storm in Dec 9 put of 10 winters had another one later in the winter?

 

[LibertyBell]

21 hours ago, nycsnow said:

Gfs has an 87mph max wind gust over the rockaways... long duration 50-70mph wind event 

 

21 hours ago, MJO812 said:

Gfs has hurricane force gusts

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?

[bluewave]

9 minutes ago, LibertyBell said:

for the rest of Dec though you dont foresee another big snowstorm correct?  This might be more like 1996 and we watch to Jan- which is fine by me.  The longer we wait the bigger it'll probably be.  Didn't someone say that when you have a 10"+ storm in Dec 9 put of 10 winters had another one later in the winter?

 

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.

[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.