donsutherland1

Yes, that is true. But it's still worth trying to identify those who routinely make irresponsibly extreme calls if the public is to be truly weather-aware.

Apparently the local NBC outlet called out one site that has been hyping coming extreme to historic cold for several weeks. Viewers were probably asking why the station wasn’t forecasting such cold. IMO, only when meteorologists start to call out their own peers for irresponsible claims will incentives for hyping events for clicks and engagement diminish. This is a welcome development.

There appears to be a significant disconnect between the snowfall forecast and QPF forecast on the National Blend of Models. Even where zero QPF is forecast, snow is forecast. I'm not aware of this issue having occurred with the prior version (4.1). I suspect that there is an adjustment algorithm concerning the edge of the snow shield that is leading to this disconnect. Taken literally, NYC would see 95:1 snow-liquid ratios. More than likely, either the QPF will prove to be higher or the snowfall will prove to be lower. Perhaps the disconnect will also disappear as the event grows nearer.

Phoenix Caps Off its Warmest Year with Its Warmest December on Record Phoenix capped off its warmest year on record with its warmest December on record. During 2024, Phoenix tied or broke 39 daily record high maximum temperatures, 42 daily record high minimum temperatures, and 43 record high mean temperatures. December has seen remarkable stability in the average monthly high temperatures. Its overall warming has been driven largely by increasing low temperatures. December 2024: Annual: During 2024, Phoenix also had an average high of 90.5° (old record: 89.8°, 1989) and an average low of 66.7° (old record: 65.5°, 2014).

A gradual transition toward sustained colder than normal weather is getting underway. Temperatures could fall to below normal readings during or after the coming weekend. The second and third weeks of January will likely feature widespread cold anomalies in much of the eastern half of the CONUS and Canada south of the Hudson and James Bays. The potential exists for widespread cold anomalies of 6°-10° below normal during that week in parts of that region, particularly the Southeast. Overall, January will likely be colder than normal in such cities as Philadelphia and New York City. Should the AO dive below -3.000, which now appears likely, the prospects for a significant or major snowfall in the New York City area could be reduced. Since 1950, a January AO ranging from -2.600 to -1.400 accounted for the largest share of 6" and 10" or above January snowfalls for storms that dumped 4" or more snow in New York City. For the 4" or above storms, 67% saw 6" or more while 56% went on to see 10" or more. When the AO was -3.000 or below, 60% of 4" or above snowstorms saw 6" or more snowfall, while 20% of those storms saw 10" or more. The exact synoptic details will be crucial to determining whether that potential will be realized. As a result, a storm that brings parts of the Middle Atlantic region a moderate snowfall Sunday night into Monday could bring only a light amount to the New York City area. It is possible that all of the snow could miss to the south of the City. Richmond will very likely see its current record streak of 1,081 days without daily 1" or greater snowfall come to an end. 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 was favored by the November run of the ECMWF for Winter 2024-2025. Even as the NAO outlook appears on course to be relatively accurate, Winter 2024-2025 will likely wind up being notably colder than the subset of winters listed above. The ENSO Region 1+2 anomaly was -0.2°C and the Region 3.4 anomaly was -1.1°C for the week centered around December 25. For the past six weeks, the ENSO Region 1+2 anomaly has averaged +0.10°C and the ENSO Region 3.4 anomaly has averaged -0.53°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 -1.97 today. The preliminary Arctic Oscillation (AO) was -1.282 today.

The AO is now forecast to drop toward -4.000 in coming days. That can lead to suppressed solutions. Indeed, the EPS 500 mb height anomalies at 132 hours illustrates the issue. I've compared the map with a cluster of 6" or greater January snowstorms for the NYC area during AO-/PNA+ regimes. That's why the best chance for accumulating snow--perhaps even a moderate snowstorm--will likely be from Philadelphia and southward. A light snowfall is possible in the NYC area, but one can't rule out the prospect that all of the snow misses to the south at this point. Put simply, the forecast pattern through at least January 10th is not conducive for KU snowstorms even as there will be sufficient cold. Richmond's ongoing record-breaking 1,081-day stretch without a 1" or above snowfall will likely end, perhaps on Sunday or Monday.

Final December numbers:

December is closing on a warmer than normal note, but a big change toward sustained colder weather lies ahead for January. The pattern will likely become more favorable for light or moderate snowfalls as the cold returns during the first week of January. The second and third weeks of January will likely feature widespread cold anomalies in much of the eastern half of the CONUS and Canada south of the Hudson and James Bays. The potential exists for widespread cold anomalies of 6°-10° below normal during that week in parts of that region, particularly the Southeast. Overall, January will likely be colder than normal in such cities as Philadelphia and New York City. Should the AO dive below -3.000, which now appears likely, the prospects for a significant or major snowfall in the New York City area could be reduced. Since 1950, a January AO ranging from -2.600 to -1.400 accounted for the largest share of 6" and 10" or above January snowfalls for storms that dumped 4" or more snow in New York City. For the 4" or above storms, 67% saw 6" or more while 56% went on to see 10" or more. When the AO was -3.000 or below, 60% of 4" or above snowstorms saw 6" or more snowfall, while 20% of those storms saw 10" or more. The exact synoptic details will be crucial to determining whether that potential will be realized. On account of a lack of snowfall, 2023-2024 will set new records for the lowest snowfall over a two-year period for Boston and New York City. Boston: 2023-2024 Total to Date: 26.9"; 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 was favored by the November run of the ECMWF for Winter 2024-2025. Even as the NAO outlook appears on course to be relatively accurate, Winter 2024-2025 will likely wind up being notably colder than the subset of winters listed above. The ENSO Region 1+2 anomaly was -0.2°C and the Region 3.4 anomaly was -1.1°C for the week centered around December 25. For the past six weeks, the ENSO Region 1+2 anomaly has averaged +0.10°C and the ENSO Region 3.4 anomaly has averaged -0.53°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 -7.58 today. The preliminary Arctic Oscillation (AO) was -0.855 today.

DCA -5.0 NYC -2.5 BOS -1.0 ORD -2.0 ATL -5.5 IAH -0.7 DEN +0.8 PHX + 3.2 SEA +3.0

Yes. It illustrates that even within a week, the ensembles can be incorrect.

The weekly outcome:

Today was an unseasonably mild day in the Mid-Atlantic region. High temperatures included: Atlantic City: 63° Baltimore: 65° Bridgeport: 56° Islip: 56° New York City: 60° Newark: 65° Norfolk: 72° Philadelphia: 66° Reading: 65° (old record: 64°, 1982) Richmond: 69° Trenton: 65° Washington, DC: 67° December will close with above to much above normal temperatures and additional 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 will likely become more favorable for moderate or perhaps larger snowfalls as the cold returns during the first week of January. The second week of January will likely feature widespread cold anomalies in much of the eastern half of the CONUS and Canada south of the Hudson and James Bays. The potential exists for widespread cold anomalies of 6°-10° below normal during that week in that region. Should the AO dive below -3.000, the prospects for a significant or major snowfall in the New York City area could be reduced. Since 1950, a January AO ranging from -2.600 to -1.400 accounted for the largest share of 6" and 10" or above January snowfalls for storms that dumped 4" or more snow in New York City. For the 4" or above storms, 67% saw 6" or more while 56% went on to see 10" or more. When the AO was -3.000 or below, 60% of 4" or above snowstorms saw 6" or more snowfall, while 20% of those storms saw 10" or more. The exact synoptic details will be crucial to determining whether that potential will be realized. On account of a lack of snowfall, 2023-2024 will set new records for the lowest snowfall over a two-year period for Boston and New York City. Boston: 2023-2024 Total to Date: 26.9"; 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 was favored by the November run of the ECMWF for Winter 2024-2025. Even as the NAO outlook appears on course to be relatively accurate, Winter 2024-2025 will likely wind up being notably colder than the subset of winters listed above. 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 +3.06 today. The preliminary Arctic Oscillation (AO) was +0.226 today. Based on sensitivity analysis applied to the latest guidance, there is an implied near 100% probability that New York City will have a colder than normal December (1991-2020 normal). December will likely finish with a mean temperature near 38.0° (1.1° below normal).

The fireworks of the December 29 0z ECMWF and GFS runs have now faded. Even as those runs aren't cast in stone, they provided a glimpse of the potential that lies ahead. A colder pattern will develop starting around January 2-3. As an AO-/PNA+ pattern develops, the potential for moderate or perhaps significant snowfalls will increase in the northern Mid-Atlantic region, including the New York City area. The cold will be in place. There will be some short waves that offer the possibility of blossoming into storms. Synoptic details will be crucial. From this far out, they can't be resolved with reliability. Individual ensemble member snowfall forecasts maintain a wide spread among dates (January 6-12). Typically, they converge on a single narrow timeframe in advance of a significant or major event. In the meantime, below are 500 mb clusters for New York City's January 6" or above snowstorms during AO-/PNA+ regimes, which are most favorable for significant events relative to climatology, for reference.

I believe we are now leaving the Holocene and perhaps have already left. It’s probably only a matter of time before geologists reach consensus.

Week ahead outlook: The coming week will be a transitional period. Very mild weather will give way to progressively colder weather. Snowfall will still likely be limited in the Mid-Atlantic and southern New England areas.

I suspect that it's a combination of both. It's too soon to be sure whether NYC is in the very early stages of a structural decline in snowfall from a warming climate. By the mid-2030s, it will probably be clear e.g., if NYC's seasonal snowfall has fallen to 20" or below (as suggested with regression analysis). Here's how NYC's 30-year mean snowfall stacks up against its 30-season winter mean temperatures: Here's Washington, DC's where seasonal snowfall has become structurally lower: Notice that both cities saw an increase as they approached mean winter temperatures of 36° that continued shortly afterward. NYC's decrease will likely be lower simply because NYC is closer to Canada and even in a warmer climate will see stronger shots of cold than Washington, DC. Both cities will remain capable of seeing big snowstorms, even as Washington's seasonal snowfall has declined and even if New York City's is in the early stages of a structural, non-cyclical decline. Both cities can still see very snowy winters. Winter 2009-10 in Washington, DC provides an example of multiple big snowstorms there and a very snowy winter despite a climate that had warmed by 1.4° over the prior 20 years.

Increasingly, it appears that credible meteorological organizations and meteorologists are being drowned out by Social Media hype by amateurs and some of their own peers. The amateurs may not necessarily know better, but one would expect that the professionals would. But exaggerated posts (snowstorms, SSWs, and severe cold) in recent years hints otherwise. Last night, the 12/28 0z ECMWF operational model forecast a historic-type Arctic blast. Several professional accounts were among Social Media accounts trumpeting the model verbatim. At least one even specifically referred to "historic cold." A turn toward colder weather is likely in early January and the second week of January could be much colder than normal. But there is a large distinction between much colder than normal, a significant Arctic blast, and a historic-type Arctic blast. If one examines the bigger picture one finds: 1. Historic-type Arctic blasts have become less common as the Arctic region has warmed and the Northern Hemisphere's deep cold pool has shrunk. The last true historic large-scale Arctic blast occurred in February 11-20, 2021. 2. The climate has warmed, particularly since 2000. The ongoing warming is a big reason why the Contiguous U.S. has not seen a winter where excessively cold minimum temperatures have exceeded areal coverage of excessively warm minimum temperatures (winter average) since 2013-2014: Here are the Northern Hemisphere temperature anomalies 2 weeks and 1 week before the start of the February 2021 historic Arctic outbreak: 2 weeks: 1 week: 3 days: And here's the latest map (December 26, 2024): Key Difference: There was much more very cold air, both on our side of the Northern Hemisphere and the Northern Hemisphere overall prior to the February 2021 Arctic outbreak. It is unclear whether those accounts have much understanding of how to use ensembles, even as they almost certainly have awareness of ensembles. IMO, those accounts would do well to visit and study WPC's outstanding ensemble training page: https://www.wpc.ncep.noaa.gov/ensembletraining/ The WPC guide notes of operational model runs: "...in a chaotic system like an atmospheric model, non linear errors (although inconsequential in short lead times) will grow - sometimes rapidly. Eventually these growing errors cause the model forecast ouput to eventually become useless." That lesson is ignored or not well-understood by the accounts hyping historic cold outbreaks some 10 days or more in the future. If one looks at the latest ECMWF Extreme Forecast Index, one sees significant, but not historic cold is currently forecast: The very cold ECMWF weekly outlook for January 6-13: That's very cold. But it doesn't match the coldest shots since 2000 in Boston, Chicago, Detroit, Indianapolis, Minneapolis, New York City, Philadelphia, and Washington, DC. All said, the recent ECMWF weeklies, including today's run, is plenty cold to communicate the message that it will likely turn significantly colder in the long-range with the potential of a severe shot of cold. Exaggeration and hype are not needed. There is no need to invoke historic Arctic outbreaks that still have very little support (occasional runs on a single model, no run-to-run continuity, no widespread ensemble or other model support), especially at timeframes when operational model skill scores are low. Speaking of very little support, the 12/28 12z ECMWF still contains an Arctic outbreak during the second week of January, but it is nowhere near as frigid as the 12/28 0z run featured and pushed on Social Media by multiple accounts. And for the Social Media accounts that hyped the 0z run, no mention whatsoever about the 12z run? What is likely? January 10-20, will likely see the temperature fall well into the teens and perhaps even single digits in New York City and Philadelphia. Boston will likely see single digits with perhaps a chance at a subzero low. Detroit , Chicago, and Indianapolis could see one or more subzero lows. None of those cities will likely see historic-type cold e.g., widespread subzero lows from Washington, DC to Boston and double-digit subzero lows in Chicago, Indianapolis, and Detroit. Some of those cities might see their coldest readings of the 2020s, but most very likely won't exceed their coldest readings since 2000. Most or all of those cities likely won't experience their coldest 7-day period since 2000. Historic-type low temperatures and 7-day mean temperatures are unlikely. And if the cold fails to measure up to the coldest Arctic outbreaks since 2000, one can expect the Social Media accounts to still claim that they were "correct" in their assessment. However, in fact, their assessment would be wrong, as the cold wasn't even three-decade cold, much less historic-type cold. The general public will then come away with yet another example that skews their perceptions of the meteorology profession, lumping in outstanding public and private sector meteorologists with those who seek Social Media clicks and engagement.

Warmer air began overspreading the region today. December will close with above to much above normal temperatures and additional periods of rain. The temperature will likely peak in the 60s in Washington, Baltimore, and Philadelphia 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. The second week of January will likely feature widespread cold anomalies in much of the eastern half of the CONUS and Canada south of the Hudson and James Bays. The potential exists for widespread cold anomalies of 6°-10° below normal during that week in that region. Should the AO dive below -3.000, the prospects for a significant or major snowfall in the New York City area could be reduced. Since 1950, a January AO ranging from -2.600 to -1.400 accounted for the largest share of 6" and 10" or above January snowfalls for storms that dumped 4" or more snow in New York City. For the 4" or above storms, 67% saw 6" or more while 56% went on to see 10" or more. When the AO was -3.000 or below, 60% of 4" or above snowstorms saw 6" or more snowfall, while 20% of those storms saw 10" or more. The exact synoptic details will be crucial to determining whether that potential will be realized. On account of a lack of snowfall, 2023-2024 will set new records for the lowest snowfall over a two-year period for Boston and New York City. Boston: 2023-2024 Total to Date: 26.9"; 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 was favored by the November run of the ECMWF for Winter 2024-2025. Even as the NAO outlook appears on course to be relatively accurate, Winter 2024-2025 will likely wind up being notably colder than the subset of winters listed above. 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 +4.72 today. The preliminary Arctic Oscillation (AO) was +0.373 today. Based on sensitivity analysis applied to the latest guidance, there is an implied near 100% probability that New York City will have a colder than normal December (1991-2020 normal). December will likely finish with a mean temperature near 37.7° (1.4° below normal).

The debate concerning the Medieval Warm Period and its comparison to the contemporary warming was largely put to rest in 2019. No period during the past 2,000 years even begins to compare to the magnitude and expanse of warmth seen during the current warm period. https://www.nature.com/articles/s41586-019-1401-2

Just so it's clear, my reference to a possible Arctic blast during the second week of January does not necessarily mean that it would be a historic shot of cold. It could still be the strongest shot of cold in parts of the Great Lakes region and Northeast, but that is not assured from this far out. Indeed, the 12/28 0z ECMWF backed off from the magnitude of cold shown on the 12/28 0z run. 12/28 0z ECMWF at 312 hours (850 mb anomalies °C): 12/28 12z ECMWF at 300 hours (850 mb anomalies °C): In terms of snowfall, a significant number of ensemble members show varying amounts of snowfall during January 6-12. If there will be a significant event, one would expect to see the ensemble members begin to converge on their timing for such an event. A large spread over dates typically favors lighter events in the short-range. In the medium- and long-range a large spread typically exists due to timing uncertainty.

Some updates on last week’s thoughts: 1. The eastern U.S. experienced its coldest weather so far this season. Lowest temperatures included: Albany: -5°, Allentown: 1°, Boston: 10°, Harrisburg: 10°, Hartford: 5°, New York City: 13°, Newark: 11°, Philadelphia: 11°, Poughkeepsie: -2°, Providence: 9°, and Washington, DC: 21°. This cold spell brought the first teens of the winter to New York City and Philadelphia. 2. Noticeably milder weather returned to the Great Lakes Region on Monday (in Chicago) and Tuesday (Detroit). Temperatures averaged more than 10° above normal in Chicago and Detroit on Thursday and Friday. Friday saw a high temperature of 52° in Chicago with a mean temperature that was 20.7° above normal. The milder air started moving into the Mid-Atlantic and southern New England regions on Friday and Saturday, which was somewhat delayed. 3. Snowfall remained limited from Washington, DC to Philadelphia. Snowfall totals for the week were: Baltimore: Trace; New York City: 1.0”; Philadelphia: 0.2”; and, Washington, DC: 0.1”. No additional snowfall is likely through the end of December in any of those cities. 4. The Pacific Northwest was warmer to much warmer than normal during the week. All days were above to much above normal in Portland. Seattle had a single below normal day (-0.1° below normal). It was also wet. The 1.11” that fell at Portland on December 25th was the second highest daily amount for that date. Five Thoughts Going Forward: 1. Detroit and Chicago will see 50° or above highs today and tomorrow, but a colder pattern will begin to develop on January 1 or 2. 2. Baltimore, Philadelphia, and Washington, DC will see highs that peak at 60° or above tomorrow and /or Monday. A colder pattern will begin to develop during January 2-3. 3. Snowfall prospects for the Great Lakes Region and Mid-Atlantic/southern New England regions will remain very limited for the week. 4. Phoenix will conclude its warmest year on record with an annual mean temperature of 78.6° (old record: 77.3°, 2017 and 2020) with its warmest December on record. Phoenix will tie its record for most consecutive lows of 40° or above (353 days, January 7 through December 25, 2014) on December 31st and then break that record the following day. 5. Blythe, CA will further extend its record 270-day stretch without measurable precipitation through the coming week. Longer-Range: A cold pattern will develop during the first week of January. The second week of January has the potential to feature widespread colder-than-normal readings before slow moderation develops near or after mid-month. An Arctic blast is possible during the second week of January. The pattern will likely become more conducive toward bigger snowfalls in the Great Lakes Region eastward to the Middle Atlantic and New England states. Whether there will be storminess to coincide with the cold will remain to be seen, as some of the long-range guidance keeps conditions relatively dry through at least the first week of January. Ensemble members hint that the January 6-12 timeframe might offer a window for storminess from the Middle Atlantic area into New England. The AO-/PNA+ pattern forecast up to at least January 20th on the latest guidance accounts for a disproportionate share of moderate or significant snowfalls in the Mid-Atlantic region. Some of the long-range guidance suggests that an EPO+/AO+/PNA- pattern could develop in late January. The change in teleconnections could coincide with the emergence of an AAM- regime. That would imply that the month of January could end with warmer than normal readings. Teleconnection forecasts beyond two weeks are not skillful.

For reference, 500 mb patterns associated with 6"+ January snowstorms in Philadelphia:

It will turn noticeably milder tomorrow as wetter weather moves in. New York City's northern and western suburbs could see some freezing rain late tonight or early tomorrow morning. By late in the day, the temperature will push into the lower and middle 40s in New York City December will close with above normal temperatures and additional 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. The second week of January will likely feature widespread cold anomalies in much of the eastern half of the CONUS and Canada south of the Hudson and James Bays. The potential exists for widespread cold anomalies of 6°-10° below normal during that week in that region. 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 -0.57 today. The preliminary Arctic Oscillation (AO) was +0.650 today. Based on sensitivity analysis applied to the latest guidance, there is an implied 99% probability that New York City will have a colder than normal December (1991-2020 normal). December will likely finish with a mean temperature near 37.4° (1.7° below normal).

It’s not a snow threat for the NYC area.

Its verification requires a major snowstorm. We’ll have to see if things come together. Such storms are uncommon.