donsutherland1

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:

HRRR for tomorrow morning:

It’s unfortunate that such an accident occurred.

Scranton -2 (tied record from 1960) and Mount Pocono -9 (old record: -6, 1989).

I didn’t.

It was a turboprop.

I believe that reference to a single measurement pertained to the measurement of snow depth for a white Christmas.

The day got off to a frigid start. The low temperature in New York City was 13° while it was 11° in Philadelphia. Outside the cities, widespread single-digit readings were recorded. Low temperatures included: Albany: -4° Allentown:1° Atlantic City: 8° Boston: 10° Bridgeport: 9° Danbury: 2° Farmingdale: 11° Groton: 7° Hartford: 5° Islip: 10° Meriden: 6° Montgomery: -5° Mount Pocono: -9° New Haven: 10° New York City-Central Park: 13° New York City-JFK Airport: 12° New York City-LaGuardia Airport: 12° Newark: 11° Oxford: 0° Philadelphia: 11° Poughkeepsie: -2° Providence: 9° Reading: 8° Trenton: 5° Westhampton: 1° White Plains:6° Wilmington, DE: 9° Worcester: 4° Tomorrow will be variably cloudy. Snow showers are likely as a clipper passes north of the region. Parts of the region could experience a heavier snow shower or snow squall that could briefly create low visibilities and drop a coating to an inch of snow with a few locally higher amounts. The cold will begin to recede late in the week. December will likely close with above normal temperatures. 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. 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: 11.6"; Record: 17.4", 1997-1998 In past days, an occasional run of the operational GFS showed a significant snowstorm from Washington, DC to New York City. However, the pattern makes such an event very unlikely for this region. Since 1950, there were 5 December snowstorms that brought 6" or more snow to all three of these cities. Four (80%) occurred with a PNA+/NAO- pattern. The NAO is forecast to be positive. In addition, three (60%) occurred when the MJO was in Phase 8, which is not likely over the next 10 days. Only the December 23-25, 1966 event produced 6" or more snow in all three cities with a positive NAO, but the AO was strongly negative (< -2.000), which is not likely during the next 10 days. In sum, the interior sections will be far more favored for an appreciable or perhaps greater snowfall than the Washington-Baltimore-Philadelphia-New York City area over the next 10 days. A smaller snowfall remains plausible, as occurred during December 20-21 and is possible from tomorrow's snow showers or snow squall. 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 -0.73 today. The preliminary Arctic Oscillation (AO) was -0.590 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).

So far, the GEFS continues to suggest that the strongest shots of cold during the evolution of a colder pattern in January will dump into the West. There remain questions about the timing of the onset of the colder pattern in the East. The EPS (through 0z) had remained faster than the GEF (through 12z). Both support the development of a pattern that could become more favorable for moderate (4"+) or, if the PNA+ persists, significant (6"+) snowstorms than has been the case all winter so far. Whether there will be short waves present to produce the storminess remains to be seen. Below are cases for severe multi-day cold shots that reached the East during the first half of January (1980-2024). Finally, the cold start to December and 1.8" snowfall to date in New York City make it unnecessary to post "winter futility charts" at this time. Indeed, out of 156 winters (which includes 2024-25), Winter 2024-25 ranks 65th worst in terms of cold and snow (standardized basis) through December 22nd for New York City.

It would be nice to see a decent snow squall give NYC enough snow to assure the 1" snow cover at 7 am 12/25. Hopefully, the high-res models will provide good insight into the intensity and duration of the possible snow squall line.