donsutherland1

I suspect that the recent evidence of declining albedo on account of cloud-related changes has essentially put the debate to rest about the impact of clouds. Cloud-related changes will have a positive feedback (amplify warming). The earlier hypothesis that clouds could offset some of the warming is being proved incorrect by the most recent evidence.

Tomorrow will be a mild day with readings rising into the lower and middle 50s across the region. Temperatures could peak in the upper 50s and lower 60s as far north as southern New England on Wednesday. A larger storm will affect the region late tomorrow night into Thursday. The storm will likely bring a general 1"-2" rainfall. Some places could see locally higher amounts of up to 3" of rain. Following this storm, it will turn briefly noticeably colder Thursday and Friday before milder air starts to return during the weekend. 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 +0.1°C and the Region 3.4 anomaly was -0.3°C for the week centered around December 4. For the past six weeks, the ENSO Region 1+2 anomaly has averaged +0.12°C and the ENSO Region 3.4 anomaly has averaged -0.20°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 continues to increase. Currently, 47% of dynamical models and 22% of the statistical models forecast the development of a La Niña. The SOI was +13.34 today. The preliminary Arctic Oscillation (AO) was -1.846 today. Based on sensitivity analysis applied to the latest guidance, there is an implied 59% 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).

Thanks. Yes, that’s true.

On ERA-5, global Temperature Anomalies are currently the second highest for 12/7 (most recent data for 2024). They are well above the 3rd highest value for this time of year.

Yes. I also, felt odds leaned cold in the East. From 11/24 in this thread: "Therefore, the odds are now tilted toward a cooler than normal December in the eastern third of the U.S. including such cities as Philadelphia, New York City, Buffalo, Chicago, Detroit, and Indianapolis, among others. Toronto could also wind up colder than normal."

Final Outcomes: The period was colder than normal but warmer than the guidance had implied.

Milder air surged back into the region to close the weekend. High temperatures included 55° in New York City and 59° in Philadelphia. Tomorrow and Tuesday will be somewhat cooler, but still on the mild side of normal. Temperatures could peak in the upper 50s and lower 60s into southern New England on Wednesday. A series of two storms will bring rain to accompany the return of milder temperatures. Tomorrow will likely see periods of rain with a general 0.25"-0.75" storm total. A larger storm will affect the region Wednesday into Thursday. At present, this storm could be capable of bringing widespread 1"-2" rainfall. Some places could see locally higher amounts of up to 3" of rain. Following two storms, it will turn briefly noticeably colder late in the week before milder air starts to return during the weekend. 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 +0.3°C and the Region 3.4 anomaly was -0.3°C for the week centered around November 27. For the past six weeks, the ENSO Region 1+2 anomaly has averaged +0.07°C and the ENSO Region 3.4 anomaly has averaged -0.23°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 continues to increase. Currently, 47% of dynamical models and 22% of the statistical models forecast the development of a La Niña. The SOI was +17.07 yesterday. The preliminary Arctic Oscillation (AO) was -1.286 today. Based on sensitivity analysis applied to the latest guidance, there is an implied 64% probability that New York City will have a colder than normal December (1991-2020 normal). December will likely finish with a mean temperature near 37.8° (1.3° below normal).

The last 7-10 days of December has remained a question mark. The 12/7 ECMWF weeklies were close to normal in the eastern half of the CONUS/Canada and warm in the western half. The CFSv2 was warmer than normal across almost all of North America. Nevertheless, some accounts on Social Media were spiking the proverbial football this afternoon for a much colder pattern even before anything had actually verified. Meanwhile, less than an hour after the festivities celebrating a dramatic turn toward a colder pattern for the Christmas/Hanukkah holiday had gotten underway, the ECMWF weeklies attempted to take away the punch bowl. Let's have a look: ECMWF 12/7 Run for 12/23-30: ECMWF 12/8 Run for 12/23-30: And how about for the following week? ECMWF 12/7 Run for 12/30-1/6: ECMWF 12/8 Run for 12/30-1/6: In reality, nothing much has changed in the larger forecasting scheme since the 0z runs. Some of the guidance has shifted colder, but the ECMWF weeklies went in the opposite direction. All of that could be noise prior to the models ultimately coming into agreement. All said, there's no major reason to move away from the idea that it could turn colder during the closing days of the month, while respecting that there is uncertainty concerning the timing of any shift should it occur. IMO, until there is sustained model commitment in one direction or the other, one should avoid prematurely verifying forecasts that may yet fail to verify. It's better to allow the passage of some time to get things right than to pre-verify an outcome that might never actually occur.

The cold start to December is on track, although readings in some places are milder than what had been shown on the guidance prior to the start of December. The first week of December saw temperatures in numerous locations in the East and Midwest average 6°-10° below normal. Some updates on last week's thoughts. 1. A clipper system brought a trace of snow to Washington, DC, New York City, and Boston. 2. Following the clipper, a number of cities in the eastern third of the U.S. experienced their lowest temperatures so far this season including Chicago, Cleveland, Detroit, Indianapolis, Norfolk, and Richmond. 3. British Columbia experienced much above normal temperatures. Five thoughts going forward: 1. A pattern change to milder weather still appears on track for mid-month. It will turn briefly very mild in the East on Tuesday and Wednesday, before another sharp cold shot brings much below normal temperatures for several days. 2. A storm will bring heavy rain to the Eastern Seaboard during late Tuesday into Thursday. An area running from Richmond to Boston could see widespread 1"-2" rainfall amounts with locally higher amounts of 3". Temperatures could surge to 60° or above in Washington, DC, Philadelphia, New York City, and perhaps Boston. Snowfall opportunities for the East Coast will remain limited through at least mid-month. 3. Minneapolis could see its first subzero low of the season on Thursday. Chicago and Milwaukee will likely experience their first single-digit temperatures of the season on Thursday. Detroit has a chance to drop below 10°. 4. After a short push of cooler air, Phoenix will see temperatures rebound into the 70s. Phoenix remains on track for a 78.3° annual mean temperature, which would surpass the existing mark of 77.3° from 2017 and 2020. 5. Overall, parts of the eastern third of the U.S. remain on course for a colder than normal December, even as the outcome of the closing week of the month remains uncertain (ECMWF weeklies are close to normal in the eastern half of the CONUS and Canada while the CFSv2 is warmer than normal across almost all of North America). Long-Range: There currently is a consensus among both long-range weekly tools that it could turn colder in early January (slower timing on the CFSv2). Supporting a faster arrival of colder air, the PNA is forecast to go positive around or just after mid-month. However, the EPO, NAO, and AO are forecast to remain largely neutral. That predominantly neutral state could persist into the start of January. The major fly in the ointment for the start of January is the risk that the PNA could go negative as shown on the 46-day EPS forecast. A PDO- supports a predominantly negative PNA. Were that outcome to verify, one could see the long-range guidance begin to shift the forecast area of cold westward as the late December period approaches. Finally, there is some disagreement among the extended GEFS and ECMWF concerning the dominant pattern regime from late December into January. The GEFS favors an Alaskan Ridge during the first week of January, which would feature colder weather in the East and warmer weather in the West. The extended ECMWF is split between an Alaskan Ridge and Pacific Ridge into mid-January. A Pacific Ridge favors cold in the West and warmth in the East. Based on the current conflicting guidance, I suspect that the first week of January could see cold redevelop, possibly even during the last few days of December, but rather than locking in initially, the pattern could feature variability. Whether the cold pattern will lock in or yield to a milder one afterward remains to be seen.

A wet week lies ahead. Midweek will be very mild before it turns sharply colder. Snowfall prospects will remain limited.

The first week of December concluded with a mean temperature of 34.7° in New York City. That was the coldest first week of December since 2007 when the mean temperature was 31.3°. Since 1980, every year with a first week December mean temperature below 38°, wound up with a monthly mean temperature below 39°. Since recordkeeping began in 1869, just 6 cases (9%) saw a monthly mean temperature of 39° or above after a first week mean below 38°. The warmest case in the period of record was 1971. The first week of December mean temperature was 34.6°. December finished with a monthly average temperature of 40.8°. Overall, the first week outcome suggests that December 2024 is on track to finish with a monthly average temperature below the normal figure of 39.1°. Baltimore, Boston, Philadelphia, and Washington, DC also saw their coldest first week of December since 2007. Richmond, which shivered under an 18° low this morning, experienced its coldest first week of December since 2002. Unlike in 2002 when Richmond saw 5.0" of snow during the first week of December, its 2024 chill occurred without any snowfall. Milder air will return to the region tomorrow to close the weekend. Temperatures could reach or exceed 50° in the northern Mid-Atlantic and southern New England areas by early next week. In addition, rainfall will likely accompany the return of milder temperatures. Monday night through Wednesday night looks particularly wet. Following the rainfall, it could turn briefly colder late in the week before milder air again returns. 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 +0.3°C and the Region 3.4 anomaly was -0.3°C for the week centered around November 27. For the past six weeks, the ENSO Region 1+2 anomaly has averaged +0.07°C and the ENSO Region 3.4 anomaly has averaged -0.23°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 continues to increase. Currently, 47% of dynamical models and 22% of the statistical models forecast the development of a La Niña. The SOI was +17.07 today. The preliminary Arctic Oscillation (AO) was -0.761 today. Based on sensitivity analysis applied to the latest guidance, there is an implied 61% 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).

Cold enough for snow works for me.

That map should not have been posted. Were it 1 to maybe 2 weeks out, then things would be different.

It seems that it will turn colder for the start of January based on the latest guidance. But that doesn't mean that there necessarily will be the kind of historic outbreak of cold that BAMWX is calling for or the severe Arctic outbreak that Bastardi is mentioning for mid or late January. Even if a colder pattern seems likely, source regions will be critical, as will the degree of blocking to sustain it.

It seems that every year he calls for major Arctic outbreaks in the very distant future (often calling for zero temperatures in NYC). Maybe he saw the BAMWX map from a few days ago and rolled it into the second half of January? What those involved in hyping on Social Media for clicks and views fail to understand is that the atmosphere is chaotic. This greatly limits model skill, especially beyond 10 days. Models, themselves, are also limited by their resolution, which further constrains model skill. Having said that, the increases in skill for seasonal (3-month) anomalies is impressive, but such skill is nowhere close to being able to consistently call out the timing of distant events and their magnitude.

Despite sunshine, the temperature topped out at 34° in Central Park. The last time New York City saw a 34° or below high temperature was January 21st when the mercury peaked at 31°. The current cold shot will be fairly shortlived. Milder air will return to the region to close the weekend. Temperatures could reach or exceed 50° in the northern Mid-Atlantic and southern New England areas by early next week. In addition, rainfall will likely accompany the return of milder temperatures. Monday night thrugh Wednesday night looks particularly wet. Following the rainfall, it could turn briefly colder late in the week before milder air again returns. 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 +0.3°C and the Region 3.4 anomaly was -0.3°C for the week centered around November 27. For the past six weeks, the ENSO Region 1+2 anomaly has averaged +0.07°C and the ENSO Region 3.4 anomaly has averaged -0.23°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 continues to increase. Currently, 47% of dynamical models and 22% of the statistical models forecast the development of a La Niña. The SOI was +23.98 today. The preliminary Arctic Oscillation (AO) was -0.167 today.

Reduced aerosols appear to have a modest impact given recent studies. But one can't rule out dynamic ECS where ECS increases at some point at higher levels of atmospheric CO2 largely due to cloud-related feedbacks. https://www.science.org/doi/10.1126/sciadv.aax1874 I suspect that at least some of the early cloud-related changes that seem to be occurring i.e., reduced lower level clouds/increased higher level clouds and the shift of such clouds northward, may actually be due to what the authors of the 2019 paper found when researching the Early Eocene warming. Aerosol reduction contributes, but more may be involved. It's easy to attribute the changes to reduced aerosols (easily identifiable "smoking gun"). It would be more worrisome if the changes are resulting largely as a consequence from the extent of humanity's carbon pollution. The former would fit within what's currently understood about the climate. The latter would raise serious questions about the limits of current understanding of climate dynamics and the potential for a change in those dynamics at some threshold of atmospheric CO2.

I think that's a fair point. Were the general public more information literate, my point would have less relevance. But issues exist. There is the public perception that even short-range forecasts are wrong. And one also sees such sentiments in news coverage of events i.e., recent claims that the devastating floods from Helene were "unexpected", comments that forecasters didn't provide sufficient warning that led to tremendous traffic jams in parts of PA, NY, and Ontario from the recent lake effect storm, etc. In such cases, the forecasts were on the mark. People had ample warning and ample time to avoid some of what took place. They chose not to respond appropriately. In cases, people don't respond, because of perceptions that forecasters exaggerate the threats or had been wrong previously. Indeed, the NWS is struggling to grapple with such matters. That's part of the reason they keep refining and revising the kinds of advisories, watches, warnings, and other products they put out. The NWS is not solely concerned with forecasting accuracy. It is also concerned with how people perceive and respond to their forecasts. The map in question was posted later in the day on X. When I came across it, I posted it here, as it provided a good example of my concerns. IMO, there is no credible basis that a map showing unprecedented cold more than 5 weeks in advance should be posted (the same would apply for extreme rainfall, snowfall, heat, etc., at such a timeframe). Posting that map was unprofessional. It provided zero public or commercial benefit. Even worse, should the map not verify--which is very likely given the extreme nature of what was depicted and low probability associated with such an extreme event--I fully expect only silence on that matter from BAMWX. BAMWX won't revisit the map, much less highlight what could be an enormous forecasting error. The average error for the four cities will likely be much larger than if one simply chose climatology for that period. Further, to show the absurdity of the map, I asked AI (GPT-4o) to generate a random anomaly at tenths of degree fahrenheit using the following prompt: "Generate a random one-week temperature anomaly in tenths of a degree Fahrenheit. The mean long-term anomaly is 0. Assume daily anomalies could range from -50 to +50. The deviations are normally distributed." The random 7-day mean output: -1.7°. I suspect what amounts to a simple guess will also do better. It may well be colder than normal in some or even all of the highlighted cities (though a warmer outcome can't be dismissed either right now). But an entire week of 20F-30F or more below normal over a large part of the northern U.S. is extremely unlikely (historic climate, warmer climate, inherent error of the guidance at 5 week or longer timeframes). Thus, even a large error will be only part of the problem. The avoidable nature of that error will also be important. As noted previously, I will post the verification here and on X.

This is an example of the hype that I was criticizing earlier: Now, let's take a look at the BAMWX extreme forecast and historic data for four cities shown in the more extreme parts of the map: Chicago, Great Falls, Indianapolis, and Madison. In three cases, the cold would be unprecedented for the period in question. While it could be colder than normal, the probability of the kind of cold shown on the map is extremely low. Moreover, one is dealing with a timeframe more than five weeks into the future where model skill is far less than climatology. Considering the timeframe, the historic data, and the smaller pool of Northern Hemisphere deep cold in the contemporary area, the kind of widespread extreme weekly anomalies shown on the map are exceptionally unlikely. Posting such a map is reckless. Moreover, even as BAMWX focuses on Indiana, the map is disconnected from Indianapolis' historic climate data. I suspect that the BAMWX forecast will be off by an average of 10° or more for these four cities and can't rule out a miss by more than 20°. I also expect that BAMWX will never verify its extreme idea. This outlook will be verified here and on X.

In the wake of today's clipper system that brought New York City and Newark their first snowfall of the season (just a trace), it will turn much colder. The temperature will struggle just to reach and exceed freezing in New York City tomorrow. The post-clipper cold shot will be fairly shortlived. Milder air will return to the region to close the weekend. Temperatures could reach or exceed 50° in the northern Mid-Atlantic and southern New England areas by early next week. The latest ECMWF weeklies have moved into agreement with the CFSv2 in showing generally above normal temperatures through much of the remainder of December. The CFSv2 remains more aggressive with the magnitude of wrmth. Beyond two weeks, skill scores are low, so the persistent warmth isn't cast in stone just yet. Moreover, short-duration cold shots remain possible. 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 +0.3°C and the Region 3.4 anomaly was -0.3°C for the week centered around November 27. For the past six weeks, the ENSO Region 1+2 anomaly has averaged +0.07°C and the ENSO Region 3.4 anomaly has averaged -0.23°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 continues to increase. Currently, 47% of dynamical models and 22% of the statistical models forecast the development of a La Niña. The SOI was +28.70 today. The preliminary Arctic Oscillation (AO) was +0.143 today.

I don't agree. Even language similar to this would be helpful: "The outcome represents our best judgment of how the pattern will evolve, but at such time frames significant changes are still possible..."

No. If one wants to forecast, one should. IMO, making the effort is worth it, as it can lead to insights and breakthroughs over time. However, forecasters who provide information to the general public should explicitly state the degree of uncertainty that is inherent in long-range forecasts. We, here, are aware of model limitations, the general public isn't. They should also verify their forecasts. The gap between the public's perceptions of forecasting skill and actual forecasting skill results from factors including the public's unfamiliarity with risk. Thus, if someone posts on, let's say X, that a very snowy pattern or blowtorch pattern will occur in late December and the outcome falls somewhere in between, the public only recalls the forecast that failed. It's even worse if the opposite outcome occurs. And because the forecasting language was definitive, the public makes no allowances for forecasting risk. They simply assume that meteorologists can't accurately forecast. In particular, the social media accounts that hype events--hype leads to greater social media engagement--are particularly damaging to the profession. By definition, every event can't be notable, much less extreme. Such events are low probability or very low probability events. Portraying events as extreme or referencing extreme events without providing sufficient context does a lot of damage. I believe the CPC has chosen to stick with probabilistic forecasts, because such forecasts convey the degree of uncertainty involved with various outcomes. Deterministic forecasts provide concrete numbers for outcomes but sacrifice the degree of risk. One can bridge the gap by conveying information about uncertainty when making a deterministic forecast. My point applies to those who are actually forecasting professionally for the public on a professional basis.

Absolutely. Much can still change.

I agree. With such low skill scores at that timeframe, they are being exceptionally bold. Even beyond two weeks, the ECMWF weeklies can have very large errors. The operational model has been jumping wildly between solutions on a run-to-run basis for the extended timeframe. The week 4 forecast has also seen significant changes in the forecast pattern over North America in recent runs. There's a lot of uncertainty. Forecasters risk big error by pouncing on the appearance of patterns they like and then assuming that nothing will change between now and the distant forecast period.

Toronto picked up 6.6 cm (2.6") of snow yesterday (the daily record of 15.2 cm/6.0" was set in 1898). It's encouraging to see parts of the Great Lakes region starting to build snow totals. It's also encouraging to see the guidance beginning to be less warm for January for that region, as it reinforces the idea of possible near to somewhat above normal snowfall there (Chicago to Toronto).