donsutherland1

Today was partly sunny and breezy. Temperatures generally topped out in the lower and middle 40s across the region. Tomorrow will be a similar day. During the second half of January, there will be some potential for snow events in the Middle Atlantic and southern New England regions, even as the forecast AO-/PNA- pattern is typically not a very snowy one. There continues to be ensemble support for a possible light snow event in the region during the January 21-23 timeframe during the passage of a strong cold front. Another timeframe highlighted by the ensembles is January 25-28. The latter period may have greater potential. However, neither period is likely to produce a significant snowfall (6" or above) for the Washington, DC to Boston corridor. AO-/PNA- patterns are typically not snowy. The frequency of measurable snowfall is just over 90% of climatology in Boston and Philadelphia and around 80% of climatology in New York City for the January 21-31, 1950-2020 period. The frequency of 2" or more daily snowfall was just above 90% of climatology for Philadelphia, but fell sharply to 50% of climatology in New York City and 65% of climatology in Boston. For daily snowfall amounts in excess of 2", the frequency fell sharply for Philadelphia. As a result, such patterns typically have produced significant snowstorms (6" or above snowfall) in the northern Middle Atlantic and southern New England regions during late January. The biggest snowfalls during an AO-/PNA- pattern during the January 20-31, 1950-2020 period were as follows: Boston: 7.3", January 21, 2011; New York City: 4.2", January 21, 2011; and, Philadelphia: 3.0", January 20, 2000. Afterward, the evolution of the AO will determine whether potential for measurable snow events will continue into February. The ENSO Region 1+2 anomaly was -0.8°C and the Region 3.4 anomaly was -1.1°C for the week centered around January 6. 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 -1.07°C. La Niña conditions will likely prevail at least through the winter. The SOI was +20.69 today. Today, the preliminary Arctic Oscillation (AO) figure was -1.579. On January 16 the MJO was in Phase 4 at an amplitude of 1.143 (RMM). The January 15-adjusted amplitude was 1.148. Following a significant stratospheric warming event, the stratosphere is now cooling. The cooling will likely accelerate during the second half of January. As is typical for vortex-splitting events, the major piece of the polar vortex migrated to Eurasia. The end result has been an absence of severe cold in much of North America. 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. Based on sensitivity analysis applied to the latest guidance, there is an implied 83% probability that New York City will have a warmer than normal January. January will likely finish with a mean temperature near 35.2°.

For another look, below is the percentage of days for select AO/PNA states and the percentage of days with 4" or greater snowfalls for New York City during the January 20-31, 1950-2020 period for each of those states: AO-/PNA+: 39% days, 67% of daily 4" or greater snowfalls AO-/PNA-: 19% days, 5% of daily 4" or greater snowfalls AO+/PNA+: 20% days, 24% of daily 4" or greater snowfalls AO+/PNA-: 22% days, 5% of daily 4" or greater snowfalls

Here you go:

All days in January or all cases? The latter would lead to a noisier outcome on account of differing wave lengths.

Still positive (+0.523). However, it is forecast to fall sharply. There is strong consensus on the guidance for the PNA to go negative over the next 5-7 days and then strongly negative afterward.

Below is a scatter diagram for New York City's daily snowfall of 4" or more during the January 21-31, 1950-2020 period based on the AO/PNA:

A few things, from my perspective: 1. I didn’t believe that the last week of January would be frigid. It will likely be solidly colder than normal, but if one is looking for a genuine Arctic blast, that does not appear to be likely. 2. There will likely be some opportunities for snowfall. But in late January, an AO-/PNA- pattern generally does not produce major snowstorms for the Philadelphia to Boston region. Once wave lengths shorten, one sees such outcomes on a more frequent basis (typically during the second half of February and onward). 3. The modeled pattern on some of the guidance is unusual for late January in that some ensemble members suggest a significant snowfall. I’m skeptical of that idea from this far out. If one were less than 72 hours out, that might be different. For purposes of illustration, below is a scatter diagram for NYC's days with 4" or more snowfall during the January 20-31, 1950-2020 period for the AO/PNA:

Morning thoughts... Today will be partly cloudy. Temperatures will likely reach the lower and perhaps middle 40s in most of the region. Likely high temperatures around the region include: New York City (Central Park): 44° Newark: 46° Philadelphia: 46° A strong cold front could move across the region late in the week bringing a period of light snow or flurries.

The storm responsible for the most recent rainfall continues to pull away from the region. Storm total rainfall amounts included: Allentown: 0.56" Boston: 1.03" Bridgeport: 0.72" Islip: 0.82" New York City: 1.16" Newark: 1.23" Philadelphia: 0.23" Providence: 1.33" Tomorrow will be partly sunny and somewhat cooler. However, additional potential for storms exists through at least the next two weeks. During the second half of January, there will be some potential for snow events in the Middle Atlantic and southern New England regions, even as the forecast AO-/PNA- pattern is typically not a very snowy one. There continues to be ensemble support for a possible snow event in the region during the January 21-23 timeframe. Another timeframe highlighted by the ensembles is January 25-28. The latter period may have greater potential. AO-/PNA- patterns are typically not snowy. The frequency of measurable snowfall is just over 90% of climatology in Boston and Philadelphia and around 80% of climatology in New York City for the January 21-31, 1950-2020 period. The frequency of 2" or more daily snowfall was just above 90% of climatology for Philadelphia, but fell sharply to 50% of climatology in New York City and 65% of climatology in Boston. For daily snowfall amounts in excess of 2", the frequency fell sharply for Philadelphia. As a result, such patterns typically have produced significant snowstorms (6" or above snowfall) in the northern Middle Atlantic and southern New England regions during late January. The biggest snowfalls during an AO-/PNA- pattern during the January 20-31, 1950-2020 period were as follows: Boston: 7.3", January 21, 2011; New York City: 4.2", January 21, 2011; and, Philadelphia: 3.0", January 20, 2000. Neither event is a certainty at this point in time. Afterward, the evolution of the AO will determine whether potential for measurable snow events will continue into February. The ENSO Region 1+2 anomaly was -0.8°C and the Region 3.4 anomaly was -1.1°C for the week centered around December 30. 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 -1.07°C. La Niña conditions will likely prevail at least through the winter. The SOI was +20.26 today. Today, the preliminary Arctic Oscillation (AO) figure was -2.042. On January 15 the MJO was in Phase 4 at an amplitude of 1.140 (RMM). The January 14-adjusted amplitude was 1.222. Following a significant stratospheric warming event, the stratosphere is now cooling. The cooling will likely accelerate during the second half of January. The mean zonal winds have reversed at 1 mb and 10 mb. They have all but died at 30 mb and might still reverse for a brief period. In the wake of this warming event, the polar vortex will split with the dominant piece will, as is typical for vortex-splitting 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. Blocking appears likely to continue into at least the last week of January. Based on sensitivity analysis applied to the latest guidance, there is an implied 80% probability that New York City will have a warmer than normal January. January will likely finish with a mean temperature near 35.2°.

Both 1997-98 and 2001-02 had only two measurable snow events.

Morning thoughts... Today will be mostly cloudy and still mild. Temperatures will likely reach the upper 40s in most of the region. Likely high temperatures around the region include: New York City (Central Park): 47° Newark: 49° Philadelphia: 48° Somewhat cooler air will arrive for tomorrow and Monday.

Readings across the Middle Atlantic and southern New England regions were much above normal during the first 15 days of January. At New York City, the mean temperature was 37.4° (4.7° above normal). A storm will bring showers and periods of rain tonight into tomorrow. A general 0.50"-1.00" is likely across the region. Parts of Long Island and New England could see 1.00"-1.50" rain. This system could mark the beginning of a more active weather pattern. During the second half of January, there will be some potential for snow events in the Middle Atlantic and southern New England regions. There has been persistent ensemble support during the January 21-23 timeframe for at least some snowfall in the region. Another timeframe highlighted by the ensembles is January 26-28. The latter period may have greater potential. Nevertheless, neither event is a certainty at this point in time. Afterward, the evolution of the AO will determine whether such potential continues into February. The ENSO Region 1+2 anomaly was -0.8°C and the Region 3.4 anomaly was -1.1°C for the week centered around December 30. 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 -1.07°C. La Niña conditions will likely prevail at least through the winter. The SOI was +22.38 today. Today, the preliminary Arctic Oscillation (AO) figure was -2.824. On January 14 the MJO was in Phase 3 at an amplitude of 1.216 (RMM). The January 13-adjusted amplitude was 1.232. Following a significant stratospheric warming event, the stratosphere is now cooling. The cooling will likely accelerate during the second half of January. The mean zonal winds have reversed at 1 mb and 10 mb. They have all but died at 30 mb and might still reverse for a brief period. In the wake of this warming event, the polar vortex will split with the dominant piece will, as is typical for vortex-splitting 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. Blocking appears likely to continue into at least the last week of January. Based on sensitivity analysis applied to the latest guidance, there is an implied 80% probability that New York City will have a warmer than normal January. January will likely finish with a mean temperature near 35.3°.

Winter 1912-13 saw just 0.3" snow following 11.4" in December (December 24, 1912). 0.1" fell during January 1-15. That's the benchmark winter for least snowfall following a December that saw 10" or more snow.

Morning thoughts... Today will be mostly cloudy and mild. Showers could arrive late in the day. Temperatures will likely reach the upper 40s in much of the region. A few locations could top out in the lower 50s. Likely high temperatures around the region include: New York City (Central Park): 48° Newark: 50° Philadelphia: 52° A storm will bring showers or periods of rain overnight into tomorrow morning.

A relatively quiet weather pattern remains in place. The dry weather could last through much of this week before a storm impacts the region late Friday or Saturday with some showers or perhaps periods of rain. The first 15 days of January are well on track toward finishing generally warmer than normal across the northeastern United States, Quebec, and much of eastern Canada overall. During the second half of January, there will be some potential for snow events in the Middle Atlantic and southern New England regions. There has been persistent ensemble support during the January 21-23 timeframe for at least some snowfall in the region. Afterward, the evolution of the AO will determine whether such potential continues into February. Uncertainty about the long-range has increased. There had been emerging ensemble guidance showing that the AO could go positive in the closing week of January, but more recent guidance shows a continuation of Arctic blocking. The ENSO Region 1+2 anomaly was -0.8°C and the Region 3.4 anomaly was -1.1°C for the week centered around December 30. 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 -1.07°C. La Niña conditions will likely prevail at least through the winter. The SOI was +20.26 today. Today, the preliminary Arctic Oscillation (AO) figure was -1.620. On January 13 the MJO was in Phase 3 at an amplitude of 1.232 (RMM). The January 12-adjusted amplitude was 1.259. Following a significant stratospheric warming event, the stratosphere is now cooling. The mean zonal winds have reversed at 1 mb and 10 mb. They could still reverse at 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. Blocking appears likely to continue into at least the last week of January. Based on sensitivity analysis applied to the latest guidance, there is an implied 82% probability that New York City will have a warmer than normal January. January will likely finish with a mean temperature near 35.5°.