donsutherland1

The final numbers:

Since December 1, 72% of days have seen a negative Arctic Oscillation (AO), including 47% during which it was -1.000 or below. The mean winter value to date is -0.871. As a result, both New York City and Philadelphia have seen their coldest start to winter since Winter 2017-2018. New York City has had a mean winter temperature of 36.5° (1.2° below normal) and Philadelphia has had a mean winter temperature of 36.5° (0.9° below normal). Tomorrow will be fair and pleasant. Temperatures will again top out in the upper 30s and lower 40s in New York City and Philadelphia. A cold front will then cross the region tomorrow night or early Tuesday morning, possibly with some snow flurries. In its wake, temperatures will again be below normal through at least Friday. An extended period of generally below normal temperatures is underway in the New York City area. The cold regime will likely last into at least the fourth week of January. The third week of January could see the month's first genuine Arctic outbreak around the the January 20-23 period. There is potential for some snow to accompany the arrival of the Arctic air. Moderation is possible during the days of January. The ENSO Region 1+2 anomaly was +0.1°C and the Region 3.4 anomaly was -0.7°C for the week centered around January 1. For the past six weeks, the ENSO Region 1+2 anomaly has averaged +0.02°C and the ENSO Region 3.4 anomaly has averaged -0.63°C. La Niña conditions are underway and will likely persist into the start of spring. The SOI was -20.82 today. The preliminary Arctic Oscillation (AO) was -1.367 today. Based on sensitivity analysis applied to the latest guidance, there is an implied 86% probability that New York City will have a colder than normal January (1991-2020 normal). January will likely finish with a mean temperature near 30.5° (3.4° below normal).

I stand corrected. They did.

With the 1/12 12z run of the ECMWF showing the possibility of another 1"+ snowfall in Atlanta (Days 9-10), it should be noted that the last winter that saw two 1" or more snowfalls in Atlanta was Winter 2017-18. For now, that's a reference point, and I have no comments on the actual amounts shown on what was an aggressive ECMWF output. We'll see how the pattern evolves.

Through January 11th, every high and low at JFK has been above that at Central Park.

Perhaps, but the long-term trend still favors wetter years. There will be internal variability on a year-to-year basis. Drier cycles will probably be wetter than they were in the past, though stuck patterns such as what occurred in October may also increase in frequency. I suspect that the difficulty using it for forecasting purposes likely precluded much discussion. There is literature that goes back to the 1980s that I'm aware of. I suspect improvement in modeling resolution, better understanding of ocean-atmosphere dynamics (including second order effects), and AI/ML may add to forecasting skill over the next decade or so. But there may still be real limits on forecasting capacity beyond 15 days even then.

I suspect that there is a cyclical component. That's part of the reason I have been cautious in noting that it is possible, but not yet certain, that NYC is in the early stages of a decline in seasonal snowfall from warming . The recent low snowfall winters are probably a combination of the two, but more time is needed. By the mid-2030s, it should be clearer as winter temperatures reach thresholds where cities such as Washington saw a decline in seasonal snowfall. Having said that, there is added moisture from the warming atmosphere, hence the big snowstorms are even bigger (1996-2016 period) than they were in the past. Moreover, there will still be snowy winters and big snowstorms for at least decades to come.

The pressure dipole that comprises the EPO is a functon of atmosphere-ocean forcing (both ways). Unfortunately, the processes are complex and not well-understood leading to forecasting challenges beyond the short-term. ENSO has an impact, but there is a lot of random variability (likely due to factors that have not been identified and/or are not well-understood). Beyond 10-14 days, EPO forecasts lack skill. This is why the long-range EPS, which has shown a shift to positive values, keeps failing when the timeframe draws closer.

Yes, 1963-64 was an El Niño winter.

And before the blizzard, December 31 1963-January 1, 1964 saw snow in the Deep South. Atlanta picked up 2.2" and Birmingham saw 8.4".

While the air mass that is likely to move into the Dakotas will likely be of Siberian origin, it is less clear whether the Siberian air will actually reach east of the Appalachians. Here's the latest Hysplit forecast for the NYC metro area:

The cold looks impressive, especially west of the Appalachians. Unlike the BAMWX 1/11-18 forecast for extreme cold, which will bust by > 20° for the forecast period, (both climo and a random number guess will easily beat its forecast), this cold shot looks to involve a genuine Arctic air mass. The previous cold has been largely from central and western Canada as per Hysplit. There are still some issues to work out about how could it gets in specific places (some disagreement between the prior 12z EPS and 0z EPS/GEFS vs. EPS). The sustained nature of the cold will lead to the eastern half seeing one of its colder Januaries in recent years. Unfortunately, anyone can throw up a social media account and claim to be a weather forecaster today. Based on the hype, it's clear that they don't understand what they are actually posting. For example, the BAM idea had Chicago with a mean temperature of -3° for the January 11-18 period. That's 1994 cold. Yet, had the site done minimal due diligence, it would have known that the cold would have been exceptional and it would also have seen that North America had been flooded with exceptionally frigid air well ahead of the Arctic outbreak that affected Chicago. This time around, there was much less frigid air on the maps. But it's easy to post models verbatim on social media, as the general public doesn't necessarily have the skill to discern junk from quality on the runs. No analysis was done, because analysis requires skill, knowledge, and expertise, which many of those sites lack. Indeed, the situation got so far out of hand that several NWS offices had to post advising the public to ignore maps being posted on social media. Finally, I'm not aware of a single such site that actually has weekly or monthly verifications. If they did, the results would be terrible. Not surprisingly, because of all the social media hype, the general public thinks meteorologists can't forecast (not actually true).

The EPS has a low of 8° in NYC and 10° in EWR. Suburbs could be below zero. The 0z EPS was notably colder than the preceding 12z run. The GEFS is not quite as cold (mid-teens) and is similar to the preceding run of the EPS.

The week ahead:

JFK: 0.4”; LGA: 0.3”

Dr. Swain is an outstanding and knowledgeable source. I'm glad to see that his work is gaining more attention and that even CNN gave him some time.

For World Weather Attribution's/Clmate Central's 2024 annual report: https://spiral.imperial.ac.uk/handle/10044/1/116443

Although it's possible, but not yet certain, that New York City is in the very early stages of a transition to lower snowfall from a warming climate, it should be noted that even in a warmer climate, both big snowstorms and snowy winters will remain possible for decades to come. Washington, DC's 7.2" snowfall on January 6 provides an example. Winters 2009-10, 2013-14, 2014-15, and 2015-16 provide examples of snowy winters there. The impacts of climate change will concern generally warmer winters, more "stuck patterns," and SST-forced changes from the increasing frequency of marine heatwaves. Nevertheless, internal variability will remain significant, even within the context of a warmer climate than the present one.

The storm that brought 2.1" of snow to Atlanta, its biggest snowstorm since January 16-17, 2018, also brought some light snow to the Northeast. Accumulations included: Allentown: 0.6" Atlantic City: 0.5" Boston: 1.5" Bridgeport: 1.2" New York City: 0.5" Newark: 0.5" Philadelphia: 0.1" Tomorrow and Monday will be fair and pleasant. Temperatures will top out in the upper 30s and lower 40s in New York City and Philadelphia. A cold front will then cross the region Monday night or early Tuesday morning, possibly with some snow flurries. In its wake, temperatures will again be below normal through at least Friday. An extended period of generally below normal temperatures is underway in the New York City area. Although this cold regime will likely extend through at least the first three weeks of January, the kind of severe cold that produces minimum temperatures below 10° in the Philadelphia to New York City areas is unlikely during that period. The cold could still peak with readings dropping into the teens and several subfreezing highs. The third week of January will likely feature a continuation of widespread cold anomalies in much of the eastern half of the CONUS and Canada south of the Hudson and James Bays. Those anomalies will likely result more from the prolonged nature of the cold than its severity. However, notable exceptions could be areas with fresh snow cover that experience strong radiational cooling. Moderation is possible during the closing week of the month. The ENSO Region 1+2 anomaly was +0.1°C and the Region 3.4 anomaly was -0.7°C for the week centered around January 1. For the past six weeks, the ENSO Region 1+2 anomaly has averaged +0.02°C and the ENSO Region 3.4 anomaly has averaged -0.63°C. La Niña conditions are underway and will likely persist into the start of spring. The SOI was -21.15 today. The preliminary Arctic Oscillation (AO) was -1.571 today. Based on sensitivity analysis applied to the latest guidance, there is an implied 79% probability that New York City will have a colder than normal January (1991-2020 normal). January will likely finish with a mean temperature near 30.7° (3.0° below normal).

Update through January 10th: Two Key Points: 1. None of the highlighted cities has seen their coldest low temperature or coldest 7-day period since 2020. The current lowest temperature and 7-day mean temperature could be surpassed later this month, but most or all areas likely won't see their coldest low temperature or coldest 7-day period of the 2020s. 2. The lack of a deep cold pool and, at least through January 10th, the failure to establish cross-polar flow has contributed to a warmer outcome than the Social Media calls for historic-type cold. In general, one should be wary of Social Media "meteorology" sites that hype extremes. There's a lot more involved than simply cutting and pasting model runs e.g., the due diligence involved in assessing the likelihood that the models will verify (in this case, the lack of an expansive pool of deep cold in the Northern Hemisphere was a glaring "red flag"). At present, I am not aware of any of the sites that had hyped coming historic-type cold even beginning to acknowledge their unfolding error. Unfortunately, as the general public was exposed to the hype, one can reasonably expect that the gap between the hype and what actually verifies will further skew public perceptions. Indeed, things are currently breaking somewhat warmer than I had anticipated in the initial post. The final numbers will be verified.

One sees the importance of bigger storms in Washington, DC where a warmer climate has reduced seasonal snowfall. For the 1999-00 through 2024-25 (through 1/10) period, days on which 4" or more snow fell accounted for 44% of seasonal snowfall. During 1999-00 through 2008-09, that figure was 31%. Since 2009-10, it has averaged 51%.

Some updates on last week’s thoughts: 1. Temperatures have averaged much below normal across the Great Lakes, Mid-Atlantic, and southern New England areas this week. Temperature anomalies from January 5-10 were as follows: Atlanta: -7.9°; Baltimore: -8.1°; Boston: -5.7°; Chicago: -3.9°; Detroit: -5.0°; Indianapolis: -9.0°; New York: -5.9°; Norfolk: -8.2°; Philadelphia: -6.6°; Raleigh: -8.7°; Richmond: -10.6°; Washington, DC: -8.0°. 2. A storm brought heavy snow from the Plains States to the Mid-Atlantic region during January 5-7. Snowfall totals included: Baltimore: 6.6”; Indianapolis: 7.8”; St. Louis: 8.5”; Richmond: 3.5”; and Washington, DC: 7.2”. These amounts were in line with what had been expected. A separate storm brought snow to the Southeast on January 10th. Amounts included: Atlanta 2.1”; Augusta: 1.0”; and Birmingham: 2.0”. The last time all three cities saw 1” or more in the same storm was February 12-13, 2014. That second storm also brought 3.0” to Richmond and 0.5” to New York City. 3. Indianapolis saw the temperature bottom out at 5° on January 9. Although Chicago saw a low temperature of 14°, Detroit saw the mercury dip to 7° on January 9. The low in Detroit was somewhat colder than had been expected in my discussion. Three Thoughts Going Forward: 1. Dry weather will continue in southern California through the week. Little or no rainfall is likely in such cities as Blythe, Camarillo, Lancaster, Los Angeles, and Palm Springs. 2. A significant (6”+) snowstorm is unlikely in the big cities of the Middle Atlantic and southern New England regions (Richmond to Boston) during the upcoming week. 3. A strong cold shot will affect the Great Lakes Region Tuesday through Thursday. Indianapolis could see the mercury dip to 0° or slightly below. Detroit and Chicago could see one or more single-digit low temperatures. This is very cold but does not rival what could reasonably be described as historic cold. Longer-Range: A slow moderation in temperatures is likely to commence late in the third week of January or during the fourth week of January. Precipitation could increase to above normal levels over the closing 7-10 days of January. The long-range guidance suggests that an EPO+/AO+/PNA- pattern could develop in early February. Initially, there will be an EPO-/AO+/PNA- pattern, which will likely close January. The change in teleconnections will coincide with the emergence of an AAM- regime. That would imply that the end of January or the start of February could see warmer than normal readings develop.

I see 1.2” at Mount Pocono for today.

The pennies, nickels, and dimes are adding up. Meanwhile, Petersburg, VA and James City, VA: 5.2".

Final season? Are you planning to move?