donsutherland1

Morning thoughts... Following this morning’s light snow and flurries, it will become partly sunny. Temperatures will likely reach the lower 40s in most of the region. Likely high temperatures around the region include: New York City (Central Park): 41° Newark: 43° Philadelphia: 43° A strong cold front could bring another period of light snow or flurries on Friday.

A quick video of this morning’s light snow:

Through the first 50 days of meteorological winter, the AO has averaged -1.900. It has been negative on 96% of days. It has been at or below -1.000 on 84% of days and at or below -2.000 on 50% of days. This blocking will likely continue into at least the closing days of January. Overnight into tomorrow morning, some snow showers and show flurries are likely. Parts of the region could pick up a coating of snow. There could be some additional opportunities for snowfall during the remainder of January, as blocking continues. However, significant or major snowstorms are probably not very likely. There continues to be ensemble support for some light snow or flurries in parts of 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 -0.3°C and the Region 3.4 anomaly was -1.2°C for the week centered around January 13. For the past six weeks, the ENSO Region 1+2 anomaly has averaged -0.73°C and the ENSO Region 3.4 anomaly has averaged -1.08°C. La Niña conditions will likely prevail at least through meteorological winter. The SOI was +22.99 today. Today, the preliminary Arctic Oscillation (AO) figure was -2.012. On January 18 the MJO was in Phase 4 at an amplitude of 0.636 (RMM). The January 17-adjusted amplitude was 1.007. 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 87% probability that New York City will have a warmer than normal January. January will likely finish with a mean temperature near 35.2°.

A quick video clip from a short time ago:

There are some differences from the pattern shown in that late December post concerning January 1-20. In this case, there is model consensus that the EPO will go negative for a time before returning to positive levels. That opens the door for some snowfall potential for the Middle Atlantic region, but that’s not a good pattern for significant (6” or above) snowfalls. It will be interesting to see what the ECMWF shows today after the 0z run had a sizable snow event.

Morning thoughts... Today will be partly sunny. Temperatures will likely reach the lower 40s in most of the region. Likely high temperatures around the region include: New York City (Central Park): 43° Newark: 44° Philadelphia: 45° A weak cold frontal passage could bring a few snow flurries tomorrow. A strong cold front could move across the region late in the week bringing a period of light snow or flurries.

No. It’s happened before. Here’s one discussion I posted concerning the January 1-20 period: https://www.americanwx.com/bb/topic/54083-december-2020-general-discussions-observations-thread/?do=findComment&comment=5773757 Through January 18, the January mean temperature is 37.9° in New York City.

New England could have some opportunities. The problem for the New York City area is the positioning of the block. It’s too far south (just as has been the case for much of this month). Of course, beyond two weeks the weeklies are little better than climatology.

Under partly sunny skies, the temperature rose into the lower and middle 40s across the region today. Tomorrow will be somewhat cooler. Meanwhile, parts of California experienced record warmth. High temperatures included: Oakland: 83° (old record: 67°, 2014) ***new January record*** Sacramento: 74° (old record: 69°, 2014) San Francisco: 74° (old record: 68°, 1948) ***tied January record*** Stockton: 78° (old record: 69°, 2009) ***new January record*** Oakland's previous earliest 80° temperature on record occurred on February 6, 2011 when the temperature reached 81°. That was Oakland's only 80° temperature on record in February. The previous earliest date on record for an 83° or above temperature was March 10, 2004 when the mercury reached 86°. Records at Oakland go back to 1948. 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 some light snow or flurries in parts of 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 -0.3°C and the Region 3.4 anomaly was -1.2°C for the week centered around January 13. For the past six weeks, the ENSO Region 1+2 anomaly has averaged -0.73°C and the ENSO Region 3.4 anomaly has averaged -1.08°C. La Niña conditions will likely prevail at least through meteorological winter. The SOI was +22.66 today. Today, the preliminary Arctic Oscillation (AO) figure was -1.507. On January 17 the MJO was in Phase 4 at an amplitude of 1.001 (RMM). The January 16-adjusted amplitude was 1.145. 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 87% probability that New York City will have a warmer than normal January. January will likely finish with a mean temperature near 35.2°.

The 12z GFS notwithstanding, a 6” or greater snowfall in the forecast pattern is not very likely. Until one is within 48-72 hours and there is much greater model consensus, the base case remains a lighter accumulation scenario.

This week’s -1.3C figure of Region 4 was the coldest since the week centered around January 25, 2012 when the anomaly was also -1.3C.

We disagree. If you don’t wish to read a thread, you are not compelled to do so. I, for one, enjoy reading well-reasoned messages. Walt Drag’s posts are outstanding (as were his AFDs for those who recall his tenure at the National Weather Service). One can see both his expertise and passion for the weather.

In December New York City received 10.5” snow. In January, just a trace of snow has fallen. The lowest January snowfall figures following a December with 10.0” or more snow were 0.1” during winter 1933-34 and 0.3” during winter 1912-13. In addition, there have been 10 cases where January received less than 6.0” snow following a December with 10.0” or more snow. In 40% of cases, the remainder of winter saw less than 10.0” snow. In 50% of cases, the remainder of the snow season saw 20.0” or more snow. In all cases during which the remainder of winter picked up more than 10.0” snow, February saw 10.0” or more snow.

The information on social media concerning such events is typically quite poor. Although a lot is still not well understood, there is a large body of evidence that displacement events typically favor North America for cold while vortex-splitting events typically favor Eurasia with the cold. This SSW fell into the latter category. Parts of Asia and Europe have seen some severe cold. Much of North America hasn’t.

First, it’s weather. Second, there is educational value e.g., Walt Drag, explained, “A NAM TSection check is showing the cold pool aloft and the RH spike but only a smattering of measurable around the NYC forum so odds favor no occurrence of 0.1" snowfall in CP.” If one goes to Bufkit, among other places, one can better see what a top meteorologist sees and learn to evaluate potential events in a fashion that can only increase one’s own skill. Third, it’s fun and interesting to read such discussions, if one enjoys meteorology.

Morning thoughts... Today will be partly to mostly sunny. Temperatures will likely reach the lower and middle 40s in most of the region. Likely high temperatures around the region include: New York City (Central Park): 45° Newark: 47° Philadelphia: 47° A strong cold front could move across the region late in the week bringing a period of light snow or flurries.

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°.