donsutherland1

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).

Arctic Report Card 2020 is now available at: https://www.arctic.noaa.gov/Portals/7/ArcticReportCard/Documents/ArcticReportCard_full_report2020.pdf

Morning thoughts... Today will be variably cloudy. Some snow flurries and snow showers are possible. A rain shower is also possible during the afternoon. Some parts of the region could pick up a coating of snow. Temperatures will likely top out in the upper 30s and lower 40s in most of the region. Likely high temperatures around the region include: New York City (Central Park): 38° Newark: 41° Philadelphia: 42° Milder air will return tomorrow and prevail through the remainder of the week.

There were flurries in parts of the area, including Central Park.

New York City received its first snowfall of winter 2020-21 today. However, it was not measurable. Just a trace of snow was reported. Through today, the preliminary AO average for December is -0.949. On 75% of days, the AO has been negative, including 63% when the AO has been -1.000 or below. Nevertheless, a warm anomaly has prevailed during the first eight days of December. Moreover, December remains likely to finish with a warm anomaly. Such situations are not common. December 2001 was one such case. The AO was negative on all 31 days and at or below -1.000 on 53% of days. The AO averaged -1.276 with a minimum value of -3.293 on December 28. At New York City, the monthly mean temperature was 44.1° (then the warmest December on record, which was eclipsed in 2015) and only a trace of snow was recorded. Tomorrow will likely remain cooler than normal. Some snow flurries and snow showers are likely. Some parts of the region could pick up a coating of snow. Afterward, milder air will move into the region. Somewhat cooler air could return to the region after next weekend. A sustained warmer pattern could begin to 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 +7.73. Today, the preliminary Arctic Oscillation (AO) figure was -1.261. On December 7 the MJO was in Phase 4 at an amplitude of 0.677 (RMM). The December 6-adjusted amplitude was 0.784. Based on the latest guidance, no significant stratospheric warming event is likely through the first two weeks of December. The warming above 3 mb in response to recent strong Wave 1 activity could abate toward or just after mid-month. 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°.

I expect that NYC will fall short of having its warmest year on record. LaGuardia has perhaps a better shot.

Morning thoughts... Clouds will yield to partly sunny skies. It will remain cool. Temperatures will likely top out in the upper 30s and lower 40s in most of the region. Likely high temperatures around the region include: New York City (Central Park): 38° Newark: 40° Philadelphia: 40° Cool temperatures should persist through tomorrow. Some snow flurries and snow showers are likely tomorrow, as well.

That happened in winter 2001-02, as well.

Earlier today, a system brought snow to parts of Virginia. Richmond picked up 1.0" snow. Another weak system could bring some snow flurries and snow showers to the region late tomorrow night or early Wednesday morning. Parts of the area could pick up a coating. Before then, tomorrow will be partly sunny and cool. Through mid-week, temperatures will run somewhat below normal. Milder weather will return for a time afterward, before the next push of cooler air arrives. Through mid-December, no exceptional cold is likely. Meanwhile, another round of near record and record warmth is likely in parts of western Canada through mid-week. A warmer pattern could begin to 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 duration of the current AO-/PNA+ pattern will be key to how long the developing colder pattern persists. Statistical guidance based on the ENSO state and teleconnections would typically favor a colder regime for the first half of December in the Middle Atlantic and southern New England regions. Both historic experience following exceptionally warm November cases suggest that a warmer than normal December remains the base case even if the first half of the month winds up colder than normal. 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 +15.15. Today, the preliminary Arctic Oscillation (AO) figure was -1.528. On December 6 the MJO was in Phase 4 at an amplitude of 0.741 (RMM). The December 5-adjusted amplitude was 1.020. Based on the latest guidance, no significant stratospheric warming event is likely through the first two weeks of December. The warming above 3 mb in response to recent strong Wave 1 activity could abate toward or just after mid-month. 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 67% probability that New York City will have a warmer than normal December. December will likely finish with a mean temperature near 40.0°.

Bamwx focuses on Indiana and the Midwest. It will likely be warmer there relative to normal than it is in the New York City area.

Morning thoughts... At 7:45 AM, Richmond reported a temperature of 32 degrees with light snow. South and east of Richmond, moderate snow was falling. This system will pass too far offshore to affect the New York City and Philadelphia areas. Today will be partly sunny, breezy and cool. Temperatures will likely top out in the upper 30s and lower 40s in most of the region. Likely high temperatures around the region include: New York City (Central Park): 39° Newark: 42° Philadelphia: 42° Cool temperatures should persist through the middle of the week.

The new weekly numbers will be in tomorrow. They will provide further insight into the evolution of the ongoing La Niña event.