December 2020 General Discussions & Observations Thread

donsutherland1 · December 15, 2020

Tomorrow will be the calm before the storm. It will be partly cloudy and chilly.

A major storm will develop and move off the northern Delmarva Peninsula and pass south of Long Island Wednesday into Thursday. There remains some uncertainty about the storm's track, which could make a large difference in snowfall amounts along parts of the coastal plain. A general 6"-12" snowfall is likely from Philadelphia to Boston with locally higher amounts. Interior sections away from the coastline have the chance to pick up as much as 18" snow.

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."

Near record to record cold could develop in northwestern Canada during the middle or latter part of this week.

A sustained warmer pattern could develop toward the winter solstice. The closing 10 days of December could wind up generally warmer than normal. The EPS weeklies and subseasonal guidance are in agreement that the last week of December will likely be warmer than normal. Uncertainty has increased, as the AO is likely to remain negative into the closing week of December and perhaps beyond it.

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 +21.43.

Today, the preliminary Arctic Oscillation (AO) figure was -2.889. That is the lowest AO value since February 1, 2019 when the AO was -3.315.

On December 13 the MJO was in Phase 5 at an amplitude of 1.486 (RMM). The December 12-adjusted amplitude was 1.526.

Based on the latest guidance, no significant stratospheric warming event is likely through the third 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 64% probability that New York City will have a warmer than normal December. December will likely finish with a mean temperature near 39.0°.

uncle W · December 15, 2020

some Dec snowstorms from the past...

CIK_62 · December 15, 2020

The next 8 days are averaging 31degs.(27/35). Making it 26degs., or -10.0.

Month to date is 42.9[+2.8]. Should be 36.8[-1.8] by the 23rd.

Snowstorm for Wed 6pm-Thurs. 9am Estimates: All models are about 12"-14" with 20-25mph non gust wind. Enormous snow rates for a few hours produce most of the total. You better use your snow blower at least once over night or you may have problems in the morning.

Watch out for a reverse Jan. 1978 forecast fiasco. Then it was 3" snow turning to rain and we got 14". Rain/Snow line kept wrinkling up the Jersey coastline, only to be forced south again. Got to within 15 miles of Sandy Hook.

34*(54%RH) here at 6am. 33* at 7am. 35* at 9am. 37* by Noon. 38* at 1pm. 39* at 2pm. 41* at 2:30pm.

donsutherland1 · December 15, 2020

Morning thoughts...

Today will partly cloudy and chilly. Temperatures will likely top out in the upper 30s and some lower 40s across most of the region. Likely high temperatures around the region include:

New York City (Central Park): 40°

Newark: 41°

Philadelphia: 41°

A significant to major Middle Atlantic and New England snowstorm (6” or more snow) is likely from tomorrow into Thursday. Boston, New York City, Newark, and Philadelphia will likely see 6”-12” with locally higher amounts. North and west of Philadelphia to New York City, an area of 12”-18” snow with some locally higher amounts is likely. Parts of the region will pick up more than a foot of snow. Near blizzard or even blizzard conditions are possible at the height of the storm tomorrow night.

CPcantmeasuresnow · December 15, 2020

These are the top 20 storms in NYC, with the storms of the 2000's highlighted in red. Amazing how they have filled the top ten in the last 20 years.

To get on the list this storm would have to exceed 15.2 inches in Central Park. I'd love to see it happen but doubting it does. More realistic is the 11.3 inches I keep touting so the 30 year average gets to 30 inches for the Jan 1991 to Dec 2020 calculations to come out next month. It would be nice to get both but I'll take the 11.3 and hope for the top 20 after that. Of course the way they measure in the Park we may not know final totals until early Friday morning, after settling and compression takes its toll.

image.png.5b76ca5aad45bd5ad5c6a96b303ce992.png

wizard021 · December 15, 2020

wizard021 · December 15, 2020

Lets supress some of the height rises in ohio valley and we might be talking.

MJO812 · December 15, 2020

Christmas coastal storm signal on the gfs

Allsnow · December 15, 2020

Looks like a cold Christmas this year. Not the typical 60 degree weather we are use to.

donsutherland1 · December 16, 2020

A major storm will develop and move off the northern Delmarva Peninsula and pass south of Long Island Wednesday into Thursday. Parts of the region will pick up a significant snowfall.

Estimated snowfall amounts include:

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

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 +19.88.

Today, the preliminary Arctic Oscillation (AO) figure was -2.891. That is the lowest AO value since February 1, 2019 when the AO was -3.315.

On December 14 the MJO was in Phase 5 at an amplitude of 1.052 (RMM). The December 13-adjusted amplitude was 1.495.

Based on the latest guidance, no significant stratospheric warming event is likely through the third 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 64% probability that New York City will have a warmer than normal December. December will likely finish with a mean temperature near 38.7°.

SACRUS · December 16, 2020

1 hour ago, Allsnow said:

Looks like a cold Christmas this year. Not the typical 60 degree weather we are use to.

we'll likely go from a very warm 12/22-24 then strong arctic front Christmas timeframe. Wonder if there is some rain - temps crash and some snow at the end. 12/25 - 28 looks cold then warming up to end the year?

uncle W · December 16, 2020

if there is a lot of snow on the ground after this storm the warm up afterwards could be limited...the ao is forecast to crash again to lower levels than today...looks interesting...hopefully something comes on the 24th-25th...

CIK62 · December 16, 2020

The next 8 days are averaging 29degs.(24/34). Making it 24degs., or -11degs.

Month to date is 42.3[+2.4]. Should be 36.0[-2.2] by the 24th.

Storm Total Forecast:

EURO 16", GFS 14", CMC 12", NAM 13".

GFS had type issues on the Cobb Method.

GFS is back to 64* on Christmas. Has been varying by 30+ degrees for days.

28* here at 4:30am. 29* (45%RH)(1030.0mb) here at 6am, m. clear. 31*(48%RH)(1028.8mb)at 9am, overcast. 33*(50%RH)(1026.3mb) at Noon.

32*(70%RH)(1023.5mb) at 3pm, snowing. 29*(99%RH)(1019.9mb)moderate, snow, gusts, cars,sidewalks, Surf Ave. are white.

TODAY IS THE 60TH ANNIVERSARY [10:30AM] OF THE MID-AIR COLLISION OVER NYC THAT KILLED 134. 11 YEAR OLD STEPHEN BALTZ WAS A TEMPORARY SOLE SURVIVOR.

THE SNOW YOU SEE IN THE PHOTOS IS FROM STORM #20 ON THE LIST.

https://www.nydailynews.com/new-york/1960-new-york-city-plane-crash-back-gallery-1.1549629

LibertyBell · December 16, 2020

22 hours ago, CPcantmeasuresnow said:

These are the top 20 storms in NYC, with the storms of the 2000's highlighted in red. Amazing how they have filled the top ten in the last 20 years.

To get on the list this storm would have to exceed 15.2 inches in Central Park. I'd love to see it happen but doubting it does. More realistic is the 11.3 inches I keep touting so the 30 year average gets to 30 inches for the Jan 1991 to Dec 2020 calculations to come out next month. It would be nice to get both but I'll take the 11.3 and hope for the top 20 after that. Of course the way they measure in the Park we may not know final totals until early Friday morning, after settling and compression takes its toll.

the biggest presolstice snowstorms were in 1948 and 1960 in the 15-16 range, interesting. Dec 2003 is right up there too and almost made it to 20 on Long Island

LibertyBell · December 16, 2020

10 hours ago, donsutherland1 said:

A major storm will develop and move off the northern Delmarva Peninsula and pass south of Long Island Wednesday into Thursday. Parts of the region will pick up a significant snowfall.

Estimated snowfall amounts include:

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

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 +19.88.

Today, the preliminary Arctic Oscillation (AO) figure was -2.891. That is the lowest AO value since February 1, 2019 when the AO was -3.315.

On December 14 the MJO was in Phase 5 at an amplitude of 1.052 (RMM). The December 13-adjusted amplitude was 1.495.

Based on the latest guidance, no significant stratospheric warming event is likely through the third 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 64% probability that New York City will have a warmer than normal December. December will likely finish with a mean temperature near 38.7°.

Don if we get 6 or more inches of snow from this storm doesn't that significantly increase the chances for a normal snowfall to even above normal snowfall winter? Also aren't the last 10 days of Dec looking much colder now with more chances of snowfall?

donsutherland1 · December 16, 2020

1 hour ago, LibertyBell said:

Don if we get 6 or more inches of snow from this storm doesn't that significantly increase the chances for a normal snowfall to even above normal snowfall winter? Also aren't the last 10 days of Dec looking much colder now with more chances of snowfall?

The historic probability of normal to above normal snowfall would increase, especially if December sees 10” or more snow. The last 10 days of December are colder than what had been modeled.

donsutherland1 · December 16, 2020

Morning thoughts...

A significant to major Middle Atlantic and New England snowstorm will impact the region later today into early tomorrow. Snow will move into Philadelphia during the afternoon and then New York City area toward or during the evening. Parts of the region will pick up more than a foot of snow. Near blizzard or even blizzard conditions are possible at the height of the storm tomorrow night.

Estimated accumulations:

Allentown: 12”-18”

Boston: 7”-14”

Bridgeport: 8”-16”

Islip: 5”-10”

New York City: 7”-14”

Newark: 7”-14”

Philadelphia: 4”-8”

Poughkeepsie: 12”-18”

Providence: 6”-12”

Since 1900, there have been only 7 years that saw a snowstorm bring 6” or more snow to Boston, New York City, and Philadelphia in December: 1909, 1912, 1945, 1947, 1960, 2009, and 2010. In some cases, winter proved to be snowier than normal. In one (1912-13), the winter saw below normal snowfall. At New York City, 11.4” snow fell on December 24. The remainder of winter saw just 3.1” snow. In stark contrast, winters 1947-48, 1960-61, 2009-10, and 2010-11 saw much additional snowfall after December.

Clouds will increase. Snow will overspread the region during the afternoon or evening. Temperatures will likely top out mainly in the lower and middle 30s across most of the region. Likely high temperatures around the region include:

New York City (Central Park): 33°

Newark: 35°

Philadelphia: 37°

In the wake of the snowstorm, temperatures will run below normal for the remainder of the week.

LibertyBell · December 16, 2020

54 minutes ago, donsutherland1 said:

Morning thoughts...

A significant to major Middle Atlantic and New England snowstorm will impact the region later today into early tomorrow. Snow will move into Philadelphia during the afternoon and then New York City area toward or during the evening. Parts of the region will pick up more than a foot of snow. Near blizzard or even blizzard conditions are possible at the height of the storm tomorrow night.

Estimated accumulations:

Allentown: 12”-18”

Boston: 7”-14”

Bridgeport: 8”-16”

Islip: 5”-10”

New York City: 7”-14”

Newark: 7”-14”

Philadelphia: 4”-8”

Poughkeepsie: 12”-18”

Providence: 6”-12”

Since 1900, there have been only 7 years that saw a snowstorm bring 6” or more snow to Boston, New York City, and Philadelphia in December: 1909, 1912, 1945, 1947, 1960, 2009, and 2010. In some cases, winter proved to be snowier than normal. In one (1912-13), the winter saw below normal snowfall. At New York City, 11.4” snow fell on December 24. The remainder of winter saw just 3.1” snow. In stark contrast, winters 1947-48, 1960-61, 2009-10, and 2010-11 saw much additional snowfall after December.

Clouds will increase. Snow will overspread the region during the afternoon or evening. Temperatures will likely top out mainly in the lower and middle 30s across most of the region. Likely high temperatures around the region include:

New York City (Central Park): 33°

Newark: 35°

Philadelphia: 37°

In the wake of the snowstorm, temperatures will run below normal for the remainder of the week.

Don, would JFK be in the same 5-10 range?

donsutherland1 · December 16, 2020

3 minutes ago, LibertyBell said:

Don, would JFK be in the same 5-10 range?

IMO, 6”-10”. Hopefully, the guidance will still improve a little as the day goes on and things will verify higher in the end.

LibertyBell · December 16, 2020

35 minutes ago, donsutherland1 said:

IMO, 6”-10”. Hopefully, the guidance will still improve a little as the day goes on and things will verify higher in the end.

New Euro looks amazing has 12 inches for extreme eastern LI

SACRUS · December 16, 2020

Still would watch strong front Christmas eve into Christmas , kind that can go from 50s and rain to temp crash and heavy snow as front moves through. Looks very cold Christmas - 12/28 before we warm back up.

Eduardo · December 16, 2020

2 hours ago, donsutherland1 said:

The historic probability of normal to above normal snowfall would increase, especially if December sees 10” or more snow. The last 10 days of December are colder than what had been modeled.

I was thinking the same thing this morning. Fellow coasties lamenting the fact that they're about to see a 6"+ snowstorm in mid December is baffling to me. Everybody in the tri-state will easily surpass @bluewave's magic 3" December snowfall total tonight and tomorrow and it looks like the month will finish with a solid -AO. That's all cause for celebration in my book, especially given how dismal things looked a few weeks back.

bluewave · December 16, 2020

37 minutes ago, Eduardo said:

I was thinking the same thing this morning. Fellow coasties lamenting the fact that they're about to see a 6"+ snowstorm in mid December is baffling to me. Everybody in the tri-state will easily surpass @bluewave's magic 3" December snowfall total tonight and tomorrow and it looks like the month will finish with a solid -AO. That's all cause for celebration in my book, especially given how dismal things looked a few weeks back.

Before I changed the title of the winter thread that I started back in October, it was about the MJO staying in 4-5 for October. I changed the title of the thread for a broader winter discussion. I actually deleted my first post which didn’t look like it may work out in November as not to get hopes up too high. It was about October La Niña forcing and seasonal snowfall. Cases focused near the Maritime Continent 4-5 usually had better snow outcomes than the IO phases back to 2000. I included the last 2 winters due to the strong Niña-like background state focusing the ridge north of Hawaii. But We have seen many Niño-like influences this month like the record NP warmth and the +AAM spike and strongest +PNA for a moderate La Niña in December. The MJO in October seemed to be hinting a better snowfall outcome this winter than the last two. Perhaps, the MJO in October can be a precursor to the amount of blocking in the winter during a La Niña even if many Niño-like features are present. There were so many conflicting features during October and November that it was really tough to know how everything would interact with each other until we got to December. This will be a first for such an extreme November to December AO reversal especially for a La Niña with record warmth in November.

October 2020 forcing closer to snowier La Niña composite since 2000

B950710B-F47D-4AD1-84DA-F496ED726ED6.png.d3251ebf13a7412fee57f486b1dafa3b.png

Snowier outcomes

AA8C65B9-6F05-498D-89AA-9927A1C64907.png.cd7c0a92e658c2928fa31ebcc4376977.png

Less snowy

13B0B30A-E3A0-4963-8958-477777B57830.png.9907397c2622ee6e8737022a929cd425.png

MJO812 · December 16, 2020

Pattern continues to look good with a threat near Christmas

Eduardo · December 16, 2020

1 hour ago, bluewave said:

Before I changed the title of the winter thread that I started back in October, it was about the MJO staying in 4-5 for October. I changed the title of the thread for a broader winter discussion. I actually deleted my first post which didn’t look like it may work out in November as not to get hopes up too high. It was about October La Niña forcing and seasonal snowfall. Cases focused near the Maritime Continent 4-5 usually had better snow outcomes than the IO phases back to 2000. I included the last 2 winters due to the strong Niña-like background state focusing the ridge north of Hawaii. But We have seen many Niño-like influences this month like the record NP warmth and the +AAM spike and strongest +PNA for a moderate La Niña in December. The MJO in October seemed to be hinting a better snowfall outcome this winter than the last two. Perhaps, the MJO in October can be a precursor to the amount of blocking in the winter during a La Niña even if many Niño-like features are present. There were so many conflicting features during October and November that it was really tough to know how everything would interact with each other until we got to December. This will be a first for such an extreme November to December AO reversal especially for a La Niña with record warmth in November.

October 2020 forcing closer to snowier La Niña composite since 2000

At first glance, I thought you had mistakenly copied and pasted the October 2020 map for the "snowier outcome" composite (which is a good thing!).

Your accounting for Niño-like and Niña-like background states is sensible, but it leads me to wonder how much the usefulness of ENSO itself as a predictor might be breaking down (or at least shifting).

Solid post, as always!

MJO812 · December 16, 2020

Merry Christmas

donsutherland1 · December 17, 2020

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.