donsutherland1

The teleconnections are forecast to move into a combination that has often been associated with moderate or significant snowstorms in New York City. Based on the 12/27 0z EPS and latest 46-day ECMWF forecast, the teleconnections could be in a favorable state through January 20th. Moderate or significant snowfalls are still infrequent events. Assuming that the favorable combination occurs and persists through January 20th, one will need to look for additional factors: - Sufficient cold: Likely through most of the period - Short waves that could become storms: Multiple candidates on the guidance through 15 days - Synoptic details: TBD (can't be reliably forecast beyond 5-7 days) With the ENSO being in a neutral-cool phase, the active subtropical jet stream that is conducive to the development of Miller A storms is less prominent. At present, the potential for at least moderate (4" or above) snowfalls will become more favorable than it has been during all of the winter so far. However, the potential still needs to be realized. Based on the statistics (1950-2024), here's what seems plausible right now for the January 1-20 period: - Measurable snowfalls: 2-4 days - 1" or more snowfall: 1-3 days - 2" or more snowfall: 1-2 days - 4" or more snowfall: 1 day Moderate snowfalls: 1 to perhaps 2 Significant snowfalls: Maybe 1

The cold will begin to recede toward the end of the week as wetter weather moves in. New York City's northern and western suburbs could see some freezing rain late tomorrow night or early Saturday morning. December will close with above normal temperatures and periods of rain. The temperature will likely peak in the 60s in Washington, Baltimore, and Philadelpia and the 50s in New York City and Boston. The opening days of January will likely also begin with above normal temperatures, but it will start to turn colder. Snowfall prospects will remain limited through the end of December. However, the pattern could become more favorable for moderate or perhaps larger snowfalls as the cold returns during the first week of January. There is growing potential for the second week of January to feature widespread cold anomalies in much of the eastern half of the CONUS and Canada south of the Hudson and James Bays. On account of a lack of snowfall, 2023-2024 will likely set a new records for the lowest snowfall over a two-year period for Boston and New York City. Boston: 2023-2024 Total to Date: 26.7"; Record: 38.2", 1979-1980 New York City: 2023-2024 Total to Date: 12.6"; Record: 17.4", 1997-1998 The NAO fell to a preliminary -2.751 on September 24th (all-time September record: -2.371, September 12, 1971). That was the 9th lowest value on record. La Niña winters following September cases where the NAO fell to -1.900 or below featured a predominantly positive NAO. The most recent such winters were 2016-2017 and 2022-2023. The mean temperatures for those winters in New York City were 39.3° and 41.0° respectively. The 1991-2020 normal value is 36.2°. A warmer to much warmer than normal outcome is favored by the November run of the ECMWF for Winter 2024-2025. The ENSO Region 1+2 anomaly was -0.2°C and the Region 3.4 anomaly was -0.8°C for the week centered around December 18. For the past six weeks, the ENSO Region 1+2 anomaly has averaged +0.17°C and the ENSO Region 3.4 anomaly has averaged -0.35°C. Neutral ENSO conditions may still evolve into a La Niña event during the winter. Uncertainty as to whether a La Niña will actually develop persists. On the December 19 outlook, 56% of dynamical models but 0% of the statistical models forecast the development of a La Niña. The SOI was +5.66 today. The preliminary Arctic Oscillation (AO) was +0.684 today. Based on sensitivity analysis applied to the latest guidance, there is an implied 97% probability that New York City will have a colder than normal December (1991-2020 normal). December will likely finish with a mean temperature near 37.2° (1.9° below normal).

Here's the data that includes percentages of January days with the select teleconnections.

An AO-/PNA+ pattern is forecast to prevail through at least the first 7-10 days of January. These patterns accounted for a disproportionate share of 6"+ snowstorms for New York City during January 1-31, 1950-2024. The AO -2.500 to 0.000/PNA 0.000 to +1.750 ranges account for 50% of such events in January. The teleconnections do not guarantee significant snowstorm. Things that will be critical: 1. Whether there are short waves that could become storms 2. The 500 mb pattern 3. Placement of synoptic features 4. A sufficiently cold air mass The potential for at least a moderate (4" or above) snowstorm will be greater than it has been during all of December. It remains to be seen whether the potential will be realized.

That's a good point. @bluewave. I just looked it up now.

Baltimore's 6"+ January Snowstorms (1950-2024):

NYC would drop 0.4° were December 2015 eliminated from the data.

I suspect that NYC's proximity to a warming ocean may be the larger driver than UHI. For example, Bridgeport has also seen a large increase in December temperatures during recent years. Apparently, the POU site has moved around a number of times. That may also impact the POU numbers. See @bluewave's post.

Yes, the clusters were only based off the 18 DCA cases. I was looking at significant snowfalls. Had I used the 4" cutoff, there would have been 24 cases.

1991-20 is much warmer than 1981-10. December 2015 played a big role in contributing to that outcome.

I will post BWI and PHL in the next day or two. I have company here.

The suburbs do better, as does IAD.

A cold but dry air mass covers the region. The cold will begin to recede toward the end of the week. December will close with above normal temperatures and periods of rain. The opening days of January will likely also begin with above normal temperatures, but it will start to turn colder. Snowfall prospects will remain limited through the end of December. However, the pattern could become more favorable for moderate or perhaps larger snowfalls as the cold returns during the first week of January. There is growing potential for the second week of January to feature widespread cold anomalies in much of the eastern half of the CONUS and Canada south of the Hudson and James Bays. On account of a lack of snowfall, 2023-2024 will likely set a new records for the lowest snowfall over a two-year period for Boston and New York City. Boston: 2023-2024 Total to Date: 26.7"; Record: 38.2", 1979-1980 New York City: 2023-2024 Total to Date: 12.6"; Record: 17.4", 1997-1998 The NAO fell to a preliminary -2.751 on September 24th (all-time September record: -2.371, September 12, 1971). That was the 9th lowest value on record. La Niña winters following September cases where the NAO fell to -1.900 or below featured a predominantly positive NAO. The most recent such winters were 2016-2017 and 2022-2023. The mean temperatures for those winters in New York City were 39.3° and 41.0° respectively. The 1991-2020 normal value is 36.2°. A warmer to much warmer than normal outcome is favored by the November run of the ECMWF for Winter 2024-2025. The ENSO Region 1+2 anomaly was -0.2°C and the Region 3.4 anomaly was -0.8°C for the week centered around December 18. For the past six weeks, the ENSO Region 1+2 anomaly has averaged +0.17°C and the ENSO Region 3.4 anomaly has averaged -0.35°C. Neutral ENSO conditions may still evolve into a La Niña event during the winter. Uncertainty as to whether a La Niña will actually develop persists. On the December 19 outlook, 56% of dynamical models but 0% of the statistical models forecast the development of a La Niña. The SOI was +14.22 today. The preliminary Arctic Oscillation (AO) was +0.284 today. Based on sensitivity analysis applied to the latest guidance, there is an implied 97% probability that New York City will have a colder than normal December (1991-2020 normal). December will likely finish with a mean temperature near 37.2° (1.9° below normal).

Since 1950, Washington, DC has seen 16 6" (15.2 cm) or greater snowstorms in January. Below are the composite 500 mb height anomalies, clusters, and teleconnection combinations for such storms for reference.

FYI, the 2002 storm saw rain transition to heavy wet snow, not the other way around.

A point worth repeating from last year, is that whether one is dealing with the MJO, teleconnections, etc., the coefficients of determination are low. Each variable has an impact on the pattern, but their explanatory power is sufficiently low that they can be overwhelmed by other variables.

The cold will begin to recede toward the end of the week. December will likely close with above normal temperatures and periods of rain. The opening days of January will likely also begin with above normal temperatures, but it will start to turn colder. Snowfall prospects will remain limited through the end of December. However, the pattern could become more favorable for moderate or perhaps larger snowfalls as the cold returns during the first week of January. There is growing potential for the second week of January to feature widespread cold anomalies in much of the eastern half of the CONUS and Canada south of the Hudson and James Bays. On account of a lack of snowfall, 2023-2024 will likely set a new records for the lowest snowfall over a two-year period for Boston and New York City. Boston: 2023-2024 Total to Date: 26.7"; Record: 38.2", 1979-1980 New York City: 2023-2024 Total to Date: 12.6"; Record: 17.4", 1997-1998 The NAO fell to a preliminary -2.751 on September 24th (all-time September record: -2.371, September 12, 1971). That was the 9th lowest value on record. La Niña winters following September cases where the NAO fell to -1.900 or below featured a predominantly positive NAO. The most recent such winters were 2016-2017 and 2022-2023. The mean temperatures for those winters in New York City were 39.3° and 41.0° respectively. The 1991-2020 normal value is 36.2°. A warmer to much warmer than normal outcome is favored by the November run of the ECMWF for Winter 2024-2025. The ENSO Region 1+2 anomaly was -0.2°C and the Region 3.4 anomaly was -0.8°C for the week centered around December 18. For the past six weeks, the ENSO Region 1+2 anomaly has averaged +0.17°C and the ENSO Region 3.4 anomaly has averaged -0.35°C. Neutral ENSO conditions may still evolve into a La Niña event during the winter. Uncertainty as to whether a La Niña will actually develop persists. On the December 19 outlook, 56% of dynamical models but 0% of the statistical models forecast the development of a La Niña. The SOI was +12.30 today. The preliminary Arctic Oscillation (AO) was -0.355 today. Based on sensitivity analysis applied to the latest guidance, there is an implied 96% probability that New York City will have a colder than normal December (1991-2020 normal). December will likely finish with a mean temperature near 37.0° (2.1° below normal).

LGA: 0.4"; JFK: 0.5"

The model support for cold in January has continued to increase. At the end of the 12z run of the GFS, the 500 mb pattern lies somewhat between Clusters 1 and 2 for multi-day outbreaks of severe cold during January 1-15. 12z GFS: The point is not to take the operational GFS verbatim, much less at the timeframe involved. The key point is that the operational GFS has taken a step toward the consistent cold being shown on the ECMWF weekly guidance. If the weekly guidance is correct, one should see the operational guidance move toward the weekly guidance. ECMWF Weeklies (12/23): As early as 240 hours, the EPS is evolving toward a colder pattern, though not a severely cold one. Source regions of the air masses will become important as the colder pattern evolves. It remains possible that the EPS is rushing the evolution. Finally, although the pattern shown is not a classic one for 6" or greater snowstorms for the first half of January in the NYC area, it is moving in a direction where the prospect of at least moderate snowfalls (4"+) will be greater than it was during all of December. Short waves and other synoptic details will be critical.

Five photos from this morning's snowfall:

The report hasn't been posted. It will likely be available after 1 pm.

From Central Park this morning: