donsutherland1

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.

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°.

For reference: Philadelphia’s 30 biggest daily snowfalls: Maximum 1-Day Total Snowfall for Philadelphia Area, PA (ThreadEx) Click column heading to sort ascending, click again to sort descending. Rank Value Ending Date Period of record: 1884-10-01 to 2020-12-13 1 27.6 1996-01-07 2 22.5 2009-12-19 3 21.9 2010-02-06 4 21.1 1983-02-11 5 19.4 2016-01-23 6 19.0 1915-04-03 7 16.0 2003-02-16 8 15.5 1909-12-26 9 14.2 2011-01-26 10 13.9 1979-02-19 11 13.5 2014-01-21 12 12.4 1978-02-06 - 12.4 1966-12-24 14 11.9 1935-01-23 15 11.7 1993-03-13 16 11.6 2010-12-26 17 11.0 1902-02-17 18 10.9 1960-12-12 19 10.8 2005-01-22 20 10.6 2006-02-12 21 10.5 1888-03-12 22 10.4 2014-02-13 23 10.0 1900-02-17 - 10.0 1899-02-13 25 9.8 1967-02-07 26 9.6 1958-03-20 27 9.3 2010-02-10 - 9.3 1978-01-20 29 9.2 1945-12-19 - 9.2 1893-01-06

Allentown: 6” or more: 98% members; 10” or more: 67% members; 12” or more: 47% members JFK: 6” or more: 78% members; 10” or more: 39% members; 12” or more: 25% members Mount Pocono: 6” or more: 98% members; 10” or more: 78% members; 12” or more: 47% members

Unfortunately, that’s the case this time around.

Morning thoughts... At 7:25 am, precipitation was moving into the region. Rain had changed to snow in a line running from East Stroudsburg, PA to Poughkeepsie. Today will mainly cloudy and cooler. Some rain that could end as snow, especially north and west of the major cities is likely. Parts of the area could pick up a minor accumulation. Temperatures will likely top out in the lower 40s this morning in most of the region. Likely high temperatures around the region include: New York City (Central Park): 40° Newark: 41° Philadelphia: 42° A significant to major Middle Atlantic and New England snowstorm (6” or more snow) is likely Wednesday into Thursday. The operational GFS, which had been the most suppressed guidance has moved closer in line with the ECMWF and GGEM Models at 6z. A look at the EPS individual members continues to show a significant to perhaps major snowstorm in much of the region. Boston: 6” or more: 84% members; 10” or more: 78% members; 12” or more: 59% members Islip: 6” or more: 90% members; 10” or more: 55% members; 12” or more: 37% members New York City (Central Park): 6” or more: 98% members; 10” or more: 80% members; 12” or more: 43% members Philadelphia: 6” or more: 49% members; 10” or more: 24% members; 12” or more: 14% members Poughkeepsie: 6” or more: 94% members; 10” or more: 78% members; 12” or more: 55% members

Most of the snow in such places as Newark, New York, and into southern New England occurs after 7 pm on Wednesday.

At 72 and 120 hours, it ranks somewhat ahead of the GFS on 500 mb verification scores.

At least right now, the higher resolution models might do better with the confluence. The GFS should probably be discounted right now.

Strong Arctic blocking continues. That blocking will likely pave the way for a significant to perhaps major Middle Atlantic and New England snowstorm Wednesday and Thursday. Significant snowfall is likely in such cities as Boston, New York City, Newark, and Philadelphia, as well as north and west of those cities. Before then, tomorrow will be cloudy and noticeably cooler. Rain is likely and parts of the region could see snow with some accumulation. A major storm will then 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. The probability of a significant snowfall (6" or more) has increased further for such cities as Philadelphia, New York City, and Boston. Select EPS Ensemble Members: 6" or more: Boston: 90% Islip: 86% New York City: 96% Philadelphia: 67% Poughkeepsie: 94% 10" or more: Boston: 75% Islip: 65% New York City: 73% Philadelphia: 39% Poughkeepsie: 68% 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 -0.5°C and the Region 3.4 anomaly was -1.1°C for the week centered around December 2. For the past six weeks, the ENSO Region 1+2 anomaly has averaged -0.77°C and the ENSO Region 3.4 anomaly has averaged -1.35°C. La Niña conditions will likely prevail at least through the winter. The SOI was +16.97. Today, the preliminary Arctic Oscillation (AO) figure was -2.734. That is the lowest AO value since December 26, 2019 when the AO was -2.773. On December 12 the MJO was in Phase 5 at an amplitude of 1.525 (RMM). The December 11-adjusted amplitude was 1.637. 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 63% probability that New York City will have a warmer than normal December. December will likely finish with a mean temperature near 39.0°.

The GFS and UKMET are both outliers. That might change when the ECMWF runs. Whether the individual EPS members and operational ECMWF maintain continuity with earlier cycles could be revealing. For now, the general idea of a potential significant snowfall that would include Philadelphia, New York City, and Boston remains reasonably intact, even as the increasing model divergence suggests some increase in uncertainty.

Morning thoughts... Today will be partly to mostly sunny and very mild. Temperatures will likely top out in the upper 50s and lower 60s in most of the region. Likely high temperatures around the region include: New York City (Central Park): 61° Newark: 62° Philadelphia: 63° Colder air will return beginning tomorrow, along with some rain with snow in parts of the region. A significant Middle Atlantic and New England snowstorm (6” or more snow) is likely Wednesday into Thursday. The operational GFS is the most suppressed guidance at present. A look at the EPS individual members shows a farther north extent of the significant snow. Boston: 6” or more: 92% members; 10” or more: 73% members New York City (Central Park): 6” or more: 86% members; 10” or more: 55% members Philadelphia: 6” or more: 35% members; 10” or more: 22% members

The major synoptic story of the opening of December is the return of the negative Arctic Oscillation (AO). Through today, the AO has been negative on 83% of days, including -1.000 or below on 67% of days. The AO has averaged -1.169 this month. 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." Colder air will return to the region after the coming weekend. The recent guidance has suggested a fairly impressive cold shot for late next week. The return of the colder air could coincide with some storminess. There is growing model and ensemble support for a significant Middle Atlantic and New England snowstorm next 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. Near record to record cold could develop in northwestern Canada during the middle or latter part of next 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 -0.5°C and the Region 3.4 anomaly was -1.1°C for the week centered around December 2. For the past six weeks, the ENSO Region 1+2 anomaly has averaged -0.77°C and the ENSO Region 3.4 anomaly has averaged -1.35°C. La Niña conditions will likely prevail at least through the winter. The SOI was +15.88. Today, the preliminary Arctic Oscillation (AO) figure was -2.549. That is the lowest AO value since December 26, 2019 when the AO was -2.773. On December 11 the MJO was in Phase 5 at an amplitude of 1.642 (RMM). The December 10-adjusted amplitude was 1.376. 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 58% probability that New York City will have a warmer than normal December. December will likely finish with a mean temperature near 39.0°.

Morning thoughts... Today will be mostly cloudy and mild. A few locations could see a shower. Temperatures will likely top out in the lower and middle 50s in most of the region. Likely high temperatures around the region include: New York City (Central Park): 56° Newark: 56° Philadelphia: 59° Next week could see the return of colder air. There is growing support for a significant Middle Atlantic and New England snowstorm for the middle of next week.

Tomorrow will be another mild day, but change is coming. Colder air will return to the region after the coming weekend. The recent guidance has suggested a fairly impressive cold shot for late next week. The return of the colder air could coincide with some storminess. There is growing potential for one or two snow events. Afterward, 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. Some uncertainty exists, as the AO is likely to remain negative at least into the closing week of December. 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 ENSO Region 1+2 anomaly was -0.5°C and the Region 3.4 anomaly was -1.1°C for the week centered around December 2. For the past six weeks, the ENSO Region 1+2 anomaly has averaged -0.77°C and the ENSO Region 3.4 anomaly has averaged -1.35°C. La Niña conditions will likely prevail at least through the winter. The SOI was +5.60. Today, the preliminary Arctic Oscillation (AO) figure was -1.851. On December 10 the MJO was in Phase 5 at an amplitude of 1.373 (RMM). The December 9-adjusted amplitude was 1.080. 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 39.5°.

Morning thoughts... Today will be mostly sunny and noticeably warmer than yesterday. Temperatures will likely top out in the lower and middle 50s in most of the region. Likely high temperatures around the region include: New York City (Central Park): 55° Newark: 55° Philadelphia: 56° Milder air will prevail through the remainder of the week. Next week could see the return of colder air. There is also strong ensemble support for at least one accumulating snow event.

With milder air moving into the region overnight, temperatures rose into the upper 40s and lower 50s today. Tomorrow will be even milder. The remainder of the week will feature above normal to perhaps some much above normal temperatures. Colder air could return to the region after next weekend. The recent guidance has suggested a more impressive cold shot than had previously been modeled. The return of the colder air could coincide with some storminess. The potential exists for at least part of the region to experience one or two snow events. 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 new subseasonal guidance are in strong agreement that the last week of December will likely be warmer than normal. The latest CFSv2 weekly guidance favors much warmer than normal readings. 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 ENSO Region 1+2 anomaly was -0.5°C and the Region 3.4 anomaly was -1.1°C for the week centered around December 2. For the past six weeks, the ENSO Region 1+2 anomaly has averaged -0.77°C and the ENSO Region 3.4 anomaly has averaged -1.35°C. La Niña conditions will likely prevail at least through the winter. The SOI was +10.79. Today, the preliminary Arctic Oscillation (AO) figure was -1.126. On December 9 the MJO was in Phase 5 at an amplitude of 1.079 (RMM). The December 8-adjusted amplitude was 0.906. 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 69% probability that New York City will have a warmer than normal December. December will likely finish with a mean temperature near 39.8°.

New analysis on Australia’s record-warm spring: http://nespclimate.com.au/record-2020-spring-event-attribution/

Morning thoughts... Overnight, warmer air began overspreading the region. Today will be partly sunny and noticeably warmer than yesterday. Temperatures will likely top out in the upper 40s and lower 50s in most of the region. Likely high temperatures around the region include: New York City (Central Park): 50° Newark: 50° Philadelphia: 50° Milder air will prevail through the remainder of the week. Next week could see the return of colder air.

Milder air is now poised to move into the region. The remainder of the week will feature above normal to perhaps some much above normal temperatures. Somewhat cooler air could return to the region after next weekend. 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 new subseasonal guidance are in strong agreement that the last week of December will likely be warmer than normal. The latest CFSv2 weekly guidance favors much warmer than normal readings. 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 ENSO Region 1+2 anomaly was -0.5°C and the Region 3.4 anomaly was -1.1°C for the week centered around December 2. For the past six weeks, the ENSO Region 1+2 anomaly has averaged -0.77°C and the ENSO Region 3.4 anomaly has averaged -1.35°C. La Niña conditions will likely prevail at least through the winter. The SOI was +5.29. Today, the preliminary Arctic Oscillation (AO) figure was -0.913. On December 8 the MJO was in Phase 5 at an amplitude of 0.901 (RMM). The December 7-adjusted amplitude was 0.678. Based on the latest guidance, no significant stratospheric warming event is likely through the first half 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 73% probability that New York City will have a warmer than normal December. December will likely finish with a mean temperature near 40.0°.

Flurries in White Plains.

34 degrees and snow in Central Park.

It was probably too light to qualify as a trace. Parts of the City received flurries yesterday. The trace initially reported at EWR was retained. JFK also reported a trace. LGA did not.

The trace was in the preliminary daily climate report, but removed from the one issued overnight.

The ground is covered by snow in Hawley, PA (northeast PA).