donsutherland1

Perhaps the recent short-term strengthening of the La Nina has contributed to this modeled outcome this time around. A gradual weakening remains far more likely than a collapse. The canonical La Nina evolution has a lot to do with the tropical forcing. But there are numerous pieces that could impact the outcome this time around, including but not limited to the evolving stratospheric warming event.

That’s far enough away that there remain alternative scenarios. The ongoing stratospheric warming event provides additional long-range uncertainty.

It’s too soon to tell. The polar vortex should remain weak through much of the month. Nevertheless, the EPS weeklies are forecasting the development of an EPO+/AO+/PNA- pattern for late January. At this point, that’s beyond their skillful range.

Morning thoughts... Today will become partly to mostly sunny. Temperatures will likely reach the lower 40s in much of the region. Likely high temperatures around the region include: New York City (Central Park): 42° Newark: 43° Philadelphia: 43° Mainly fair and somewhat milder than normal temperatures will prevail through much of the week.

A relatively quiet weather pattern is in place. Through Friday, partly to mostly sunny and milder than normal conditions will likely prevail. The likely continuation of Arctic blocking through at least January 15 would typically provide a higher than climatological probability for above normal snowfall. Ideally, an expansive block would be anchored across the Baffin Bay or Greenland, not south of the Davis Strait. Blocks that are anchored near Newfoundland and Labrador can inhibit opportunities for snowfall and result in warmer to much warmer than normal conditions in the Middle Atlantic and southern New England regions. This is now the most likely scenario for much of the first half of January. Under this scenario, the first 10-15 days of January will likely be generally warmer to perhaps much warmer than normal across the northeastern United States, Quebec, and much of eastern Canada. After January 10, the EPS continues to shows a transition during which a trough will move into the East. Arctic air will likely shift mainly to Eurasia. However, the evolving pattern could be sufficiently cold to afford opportunities for snowfall if the pattern evolves as currently shown on the EPS. It remains possible that the pattern evolution could lead to a multiweek period with higher than climatological potential for snowfall. The ENSO Region 1+2 anomaly was -1.3°C and the Region 3.4 anomaly was -1.2°C for the week centered around December 30. For the past six weeks, the ENSO Region 1+2 anomaly has averaged -0.80°C and the ENSO Region 3.4 anomaly has averaged -1.10°C. La Niña conditions will likely prevail at least through the winter. The SOI was +20.07 today. Today, the preliminary Arctic Oscillation (AO) figure was -3.430. On January 4 the MJO was in Phase 3 at an amplitude of 0.910 (RMM). The January 3-adjusted amplitude was 0.762. A significant stratospheric warming event is underway. The mean zonal winds has reversed at 1 mb and will likely reverse at 10 mb and possibly 30 mb. In the wake of this warming event, the polar vortex will likely split. The dominant piece will, as is typical with such events, migrate to Eurasia. The significant December 16-17 snowstorm during what has been a blocky December suggests that seasonal snowfall prospects have increased especially from north of Philadelphia into southern New England. At New York City, there is a high probability based on historic cases that an additional 20" or more snow will accumulate after December. Were blocking to disappear, snowfall prospects would diminish. For now, blocking appears likely to continue through at least the first half of January.

That system has been in the ECMWF for 3 if the last 5 0z/12z runs. Details have differed, but there’s some potential.

The pattern transition should occur during January 10-15. It would be nice to get something during that timeframe, but it isn't assured. Then, there could be 2 to maybe 4 weeks where there is potential. Patterns with potential don't always produce, though, but we'll see how things unfold.

The 1983 data was ultimately validated. I had emailed on this topic in the past. Here’s the response: Back in late 2011 when we had a very wet year around here, WFO OKX, Eastern Region Headquarters and what was then NCDC held a teleconference to discuss the 1983 total for Central Park since it was left as a cliffhanger since 1983. It was decided after that call to accept the values as initially reported based on some additional data quality analysis and comparisons conducted with surrounding stations based on trends over many years before and since 1983. There never was any further follow up done by NCDC on those initial 1983 until this call took place in 2011 as was initially mentioned back in the mid 1980s.

Morning thoughts... Today will become partly sunny. It will be milder than normal. Temperatures will likely reach the lower 40s across much of the region. Likely high temperatures include: New York City (Central Park): 41° Newark: 42° Philadelphia: 43° The quiet weather pattern will continue at least through Friday.

Following yesterday's system that brought rain and snow to parts of the region, a quieter pattern has now settled in. Through Friday, partly to mostly sunny and milder than normal conditions will likely prevail. The likely continuation of Arctic blocking through at least January 15 would typically provide a higher than climatological probability for above normal snowfall. Ideally, an expansive block would be anchored across the Baffin Bay or Greenland, not south of the Davis Strait. Blocks that are anchored near Newfoundland and Labrador can inhibit opportunities for snowfall and result in warmer to much warmer than normal conditions in the Middle Atlantic and southern New England regions. This is now the most likely scenario for much of the first half of January. Under this scenario, the first 10-15 days of January will likely be much warmer than normal across the northeastern United States, Quebec, and much of eastern Canada. After January 10, the EPS continues to show a possible transition that could lead to a trough's moving into the East. Arctic air will likely shift mainly to Eurasia. However, the evolving pattern could be sufficiently cold to afford opportunities for snowfall if the pattern evolves as currently shown on the EPS. It remains possible that the pattern evolution could lead to a multiweek period with higher than climatological potential for snowfall. The ENSO Region 1+2 anomaly was -1.3°C and the Region 3.4 anomaly was -1.2°C for the week centered around December 30. For the past six weeks, the ENSO Region 1+2 anomaly has averaged -0.80°C and the ENSO Region 3.4 anomaly has averaged -1.10°C. La Niña conditions will likely prevail at least through the winter. The SOI was +25.40 today. Today, the preliminary Arctic Oscillation (AO) figure was -2.711. On January 3 the MJO was in Phase 3 at an amplitude of 0.754 (RMM). The January 2-adjusted amplitude was 0.692. A significant stratospheric warming event is underway. The mean zonal winds has reversed at 1 mb and will likely reverse at 10 mb and possibly 30 mb. In the wake of this warming event, the polar vortex will likely split. The dominant piece will, as is typical with such events, migrate to Eurasia. The significant December 16-17 snowstorm during what has been a blocky December suggests that seasonal snowfall prospects have increased especially from north of Philadelphia into southern New England. At New York City, there is a high probability based on historic cases that an additional 20" or more snow will accumulate after December. Were blocking to disappear, snowfall prospects would diminish. For now, blocking appears likely to continue through at least the first half of January.

True, but nothing severely cold.

Unfortunately, this is very consistent with splitting polar vortexes. A less cold but snowy pattern is still possible, though.

Morning thoughts... Today will be partly sunny and milder than yesterday. Temperatures will likely reach the lower and middle 40s in much of the region. Likely high temperatures around the region include: New York City (Central Park): 42° Newark: 44° Philadelphia: 44° Mainly fair and somewhat milder than normal temperatures will prevail through much of the week.

A developing storm was bringing rain and snow to parts of the region this evening. Tomorrow will be drier, milder, with partly sunny skies. The likely continuation of Arctic blocking through at least the first 10 days of January would typically provide a higher than climatological probability for above normal snowfall. Ideally, an expansive block would be anchored across the Baffin Bay or Greenland, not south of the Davis Strait. Blocks that are anchored near Newfoundland and Labrador can inhibit opportunities for snowfall and result in warmer to much warmer than normal conditions in the Middle Atlantic and southern New England regions. This is now the most likely scenario for much of the first half of January. Under this scenario, the first 10-15 days of January will likely be much warmer than normal across the northeastern United States, Quebec, and much of eastern Canada. After January 10, the EPO continues to show a possible transition that could lead to a trough's moving into the East. Arctic air will likely shift mainly to Eurasia. However, the evolving pattern could be sufficiently cold to afford opportunities for snowfall if the pattern evolves as currently shown on the EPS. The ENSO Region 1+2 anomaly was -1.1°C and the Region 3.4 anomaly was -0.9°C for the week centered around December 23. For the past six weeks, the ENSO Region 1+2 anomaly has averaged -0.70°C and the ENSO Region 3.4 anomaly has averaged -1.15°C. La Niña conditions will likely prevail at least through the winter. The SOI was +23.42 today. Today, the preliminary Arctic Oscillation (AO) figure was -2.437. On January 2 the MJO was in Phase 3 at an amplitude of 0.691 (RMM). The January 1-adjusted amplitude was 0.640. A significant stratospheric warming event is now in its early stages. The highest levels of the stratosphere will continue to warm through the first half of the first week of January. The mean zonal winds will likely reverse at 1 mb, 10 mb, and 30 mb making this a major warming event. Toward the end of the first week in January, the top layers of the stratosphere will likely begin to cool. The significant December 16-17 snowstorm during what has been a blocky December suggests that seasonal snowfall prospects have increased especially from north of Philadelphia into southern New England. At New York City, there is a high probability based on historic cases that an additional 20" or more snow will accumulate after December. Were blocking to disappear, snowfall prospects would diminish. For now, blocking appears likely to continue through at least the first half of January.

Morning thoughts... At 8 am, precipitation was advancing north and eastward through eastern Pennsylvania and central New Jersey. Rain was falling at such locations as Atlantic City and Philadelphia. Snow was falling just south of Allentown. Rain and sleet will move into Newark and New York City this morning and continue into the evening. Well north and west of those cities, there will be accumulating snow with 2”-4” and some locally higher amounts likely. Temperatures will likely reach the upper 30s and perhaps lower 40s in much of the region. Likely high temperatures around the region include: New York City (Central Park): 39° Newark: 40° Philadelphia: 42° Drier weather will return tomorrow.

Colder weather will return tonight into tomorrow. Tomorrow will see increasing clouds. A cold rain will overspread the Philadelphia, Newark, and New York City. Some sleet or wet snow is possible at the onset. North and west of the cities, there could be some accumulations. Poughkeepsie and Hartford could see 2"-4" snow. Boston could pick up 1"-2". Afterward, a generally mild regime will likely prevail. The likely continuation of Arctic blocking through at least the first 10 days of January would typically provide a higher than climatological probability for above normal snowfall. Ideally, an expansive block would be anchored across the Baffin Bay or Greenland, not south of the Davis Strait. Blocks that are anchored near Newfoundland and Labrador can inhibit opportunities for snowfall and result in warmer to much warmer than normal conditions in the Middle Atlantic and southern New England regions. This is now the most likely scenario for much of the first half of January. Under this scenario, the first 10-15 days of January will likely be much warmer than normal across the northeastern United States, Quebec, and much of eastern Canada. After January 10, the EPO continues to show a possible transition that could lead to a trough's moving into the East. Arctic air will likely shift mainly to Eurasia. However, the evolving pattern could be sufficiently cold to afford opportunities for snowfall if the pattern evolves as currently shown on the EPS. The ENSO Region 1+2 anomaly was -1.1°C and the Region 3.4 anomaly was -0.9°C for the week centered around December 23. For the past six weeks, the ENSO Region 1+2 anomaly has averaged -0.70°C and the ENSO Region 3.4 anomaly has averaged -1.15°C. La Niña conditions will likely prevail at least through the winter. The SOI was +18.05 today. Today, the preliminary Arctic Oscillation (AO) figure was -2.910. On January 1 the MJO was in Phase 3 at an amplitude of 0.640 (RMM). The December 31-adjusted amplitude was 0.568. A significant stratospheric warming event is now in its early stages. The highest levels of the stratosphere will continue to warm through the first half of the first week of January. The mean zonal winds will likely reverse at 1 mb, 10 mb, and 30 mb making this a major warming event. Toward the end of the first week in January, the top layers of the stratosphere will likely begin to cool. The significant December 16-17 snowstorm during what has been a blocky December suggests that seasonal snowfall prospects have increased especially from north of Philadelphia into southern New England. At New York City, there is a high probability based on historic cases that an additional 20" or more snow will accumulate after December. Were blocking to disappear, snowfall prospects would diminish. For now, blocking appears likely to continue through at least the first half of January.

I added the NAO, along with ISP.

The AO/PNA data for the most recent storm (December 16-17) will be added once the final numbers are available in a few days.

Morning thoughts... Today will be partly sunny and mild. Temperatures will likely reach the lower 50s in much of the region. Likely high temperatures around the region include: New York City (Central Park): 53° Newark: 53° Philadelphia: 54° Clouds will increase tomorrow as another storm approaches the region. Some accumulating snow is a possibility to the north and west of New York City and Newark. From Philadelphia to New York City, mainly or all rain is likely. Boston could see some accumulation of snow.

@LibertyBell, I have created a quick table for the 6" or greater snowstorms for the NYC area locations. JFK had no snow data until 1959. The table can be found at: https://public.tableau.com/profile/don.sutherland#!/vizhome/NYCArea6Snowstorms/Dashboard1

An area of sleet changing to rain moved into the big cities of the northern Middle Atlantic region this afternoon. Overnight, periods of rain are likely and the temperature will likely hold steady and then begin to rise. Tomorrow will become partly sunny and much milder. Readings will likely rise into the 50s in much of the region. The likely continuation of Arctic blocking through at least the first 10 days of January would typically provide a higher than climatological probability for above normal snowfall. Ideally, an expansive block would be anchored across the Baffin Bay or Greenland, not south of the Davis Strait. Blocks that are anchored near Newfoundland and Labrador can inhibit opportunities for snowfall and result in warmer to much warmer than normal conditions in the Middle Atlantic and southern New England regions. This is now the most likely scenario for much of the first half of January. Under this scenario, the first 10-15 days of January will likely be much warmer than normal across the northeastern United States, Quebec, and much of eastern Canada. After January 10, the EPO continues to show a possible transition that could lead to a trough's moving into the East. The ENSO Region 1+2 anomaly was -1.1°C and the Region 3.4 anomaly was -0.9°C for the week centered around December 23. For the past six weeks, the ENSO Region 1+2 anomaly has averaged -0.70°C and the ENSO Region 3.4 anomaly has averaged -1.15°C. La Niña conditions will likely prevail at least through the winter. The SOI was +15.27 today. Today, the preliminary Arctic Oscillation (AO) figure was -2.950. On December 31 the MJO was in Phase 3 at an amplitude of 0.566 (RMM). The December 30-adjusted amplitude was 0.460. A significant stratospheric warming event is now in its early stages. The highest levels of the stratosphere will continue to warm through the first half of the first week of January. The mean zonal winds will likely reverse at 1 mb, 10 mb, and 30 mb making this a major warming event. Toward the end of the first week in January, the top layers of the stratosphere could begin to cool. The significant December 16-17 snowstorm during what has been a blocky December suggests that seasonal snowfall prospects have increased especially from north of Philadelphia into southern New England. At New York City, there is a high probability based on historic cases that an additional 20" or more snow will accumulate after December. Were blocking to disappear, snowfall prospects would diminish. For now, blocking appears likely to continue through at least the first half of January. In large account due to a very warm start to the month, January will likely feature above to much above normal temperatures across the northern Middle Atlantic and southern New England regions.

I will have to work on that. It will require some time.

Morning thoughts... Clouds will increase this morning. The line of precipitation currently stretching from central Virginia northwestward into Indiana will reach the region this afternoon or evening. Some mixed or frozen precipitation is possible far north and west of New York City. Elsewhere, periods of rain are likely. Temperatures will likely reach the lower 40s across much of the region. Afterward, temperatures could hold steady or slowly rise overnight. Likely high temperatures include: New York City (Central Park): 43° Newark: 44° Philadelphia: 44° The first 10 days of January will likely feature much above normal temperatures. Afterward, a somewhat colder and potentially snowier pattern could evolve. 30-Day Verification: New York City (Central Park): Average daily forecast: 43.4° Average temperature: 43.8° Average error: 1.3° Newark: Average daily forecast: 44.6° Average temperature: 44.5° Average error: 1.2° Philadelphia: Average daily forecast: 45.1° Average temperature: 45.2° Average error: 1.3°

December is ending with a monthly mean temperature of 39.2° (1.7° above normal). The warmer than normal December was consistent with historic experience following an exceptionally warm November. Nevertheless, parts of the region are currently above normal in terms of seasonal snowfall. Seasonal snowfall amounts to date include: Albany: 27.4" (10.6" above normal) Baltimore: 1.6" (1.8" below normal) Binghamton: 51.6" (27.0" above normal) Boston: 17.3" (10.0" above normal) Bridgeport: 10.0" (4.2" above normal) Buffalo: 33.8" (2.4" below normal) Burlington: 10.9" (12.4" below normal) Caribou: 34.4" (0.7" below normal) Harrisburg: 11.7" (6.0" above normal) Islip: 7.5" (1.6" above normal) New York City: 10.5" (5.4" above normal) Newark: 11.9" (6.1" above normal) Philadelphia: 6.6" (2.9" above normal) Portland: 20.1" (5.0" above normal) Providence: 10.0" (0.2" below normal) Washington, DC: Trace (2.8" below normal) The preliminary AO average for December was -1.673. The AO was negative on 87% of days, at or below -1.000 on 77% of days, and at or below -2.000 on 35% of days. The likely continuation of Arctic blocking through at least the first 10 days of January would typically provide a higher than climatological probability for above normal snowfall. Ideally, an expansive block would be anchored across the Baffin Bay or Greenland, not south of the Davis Strait. Blocks that are anchored near Newfoundland and Labrador can inhibit opportunities for snowfall and result in warmer to much warmer than normal conditions in the Middle Atlantic and southern New England regions. This is now the most likely scenario for much of the first half of January. Under this scenario, the first 10-15 days of January will likely be much warmer than normal across the northeastern United States, Quebec, and much of eastern Canada. After January 10, there is some indication on the EPS that a transition that could lead to a trough's moving into the East could get underway. The ENSO Region 1+2 anomaly was -1.1°C and the Region 3.4 anomaly was -0.9°C for the week centered around December 23. For the past six weeks, the ENSO Region 1+2 anomaly has averaged -0.70°C and the ENSO Region 3.4 anomaly has averaged -1.15°C. La Niña conditions will likely prevail at least through the winter. The SOI was +32.12 today. Today, the preliminary Arctic Oscillation (AO) figure was -2.984. On December 30 the MJO was in Phase 3 at an amplitude of 0.457 (RMM). The December 29-adjusted amplitude was 0.356. A significant stratospheric warming event is now in its early stages. The highest levels of the stratosphere will continue to warm through the first half of the first week of January. The mean zonal winds will likely reverse at 1 mb, 10 mb, and 30 mb making this a major warming event. Toward the end of the first week in January, the top layers of the stratosphere could begin to cool. The significant December 16-17 snowstorm during what has been a blocky December suggests that seasonal snowfall prospects have increased especially from north of Philadelphia into southern New England. At New York City, there is a high probability based on historic cases that an additional 20" or more snow will accumulate after December. Were blocking to disappear, snowfall prospects would diminish. For now, blocking appears likely to continue through at least the first half of January. In large account due to a very warm start to the month, January will likely feature above to much above normal temperatures across the northern Middle Atlantic and southern New England regions.

In coming days, a positive to strongly positive EPO will coincide with a negative to strongly negative AO. Since 1950, there were 13 cases where the EPO was +1.000 or above while the AO was -1.500 or below for at least three consecutive days during the January 1-20 period. In 3 cases, the Arctic block extended southward into the Middle Atlantic region (January 1-4, 1955; January 15-17, 1998; and, January 1-3, 2003). The composite pattern is one that favors above to much above normal temperatures and little or no snowfall through at least the first 10 days of January in much or all of the Middle Atlantic Region and southern New England. Central and Upstate New York, along with central and northern New England would have greater opportunities for snowfall. Based on the latest guidance, there is a growing possibility that New York City’s Central Park could have a mean temperature of 40° or above during the January 1-10 period. There have been 20 prior cases since record-keeping began in 1869. It still appears possible that the January 10-15 period could mark a transition to a potentially snowier pattern. The key will be the continuation of Arctic blocking. Following such warm starts to January, 60% of the above cases saw less than 2” snow during the second half of January. However, in the 30% of cases with 4” or more snow during the second half of January, the AO was predominantly negative. Half of those cases saw 10” or more snow during the second half of January (1907, 1966, and 2005). Although a continuation of Arctic blocking cannot ensure a snowy second half of January—1998 is one such exception, largely on account of the super El Niño—the general absence of such blocking has seen little or no snowfall during the January 16-31 period following such warm starts to January. Things to watch for going forward if a snowy second half of January is likely: Continuation or reinforcement of the persistent AO- regime Development of a trough underneath the block that extends into the Middle Atlantic region The coldest air in the hemisphere will likely be focused on Europe on account of what increasingly looks like a polar vortex-splitting major stratospheric warming event. Severe cold’s migration to Europe does not mean that snowfall will be lacking. In the meantime, inspired by the work of Hooralph, here’s a sortable table of New York City’s 10” or greater snowstorms (1950-present): https://public.tableau.com/profile/don.sutherland#!/vizhome/NYC10Snowstorms1950-Present/Dashboard1