donsutherland1

The 0z EPS rolls the cold forward pretty much as one would expect with a WPO-/EPO-/AO-/PNA- pattern evolution. One sees how the Great Lakes/Upper Midwest is the focus of the cold while warmth proves very persistent in the Southeast. 288 hours: 312 Hours: 336 Hours: 360 Hours: The usual caveats concerning skill apply that these timeframes. Moreover, how the stratospheric warming propagates will influence the pattern evolution for the second half of the month.

I wanted to illustrate that CPC isn’t panicking. This map at that timeframe is along the lines of what many of us are thinking. It’s very close to my baseline scenario.

The latest week 3-4 CPC outlook:

That's a great map.

A generally milder than normal pattern will likely continue through next Wednesday. However, exceptional warmth appears unlikely. The closing days of November will likely turn colder. Meanwhile, today will be Central Park's 1,392nd consecutive day without daily snowfall of 4" or more. The record of 1,394 days was set during February 22, 1929 through December 16, 1932. That stretch ended with 6.7" daily snowfall on December 17, 1932. The ENSO Region 1+2 anomaly was -0.7°C and the Region 3.4 anomaly was -0.7°C for the week centered around November 12. For the past six weeks, the ENSO Region 1+2 anomaly has averaged -0.16°C and the ENSO Region 3.4 anomaly has averaged -0.65°C. La Niña conditions will likely continue through at least mid-winter. The SOI was +26.47 today. The preliminary Arctic Oscillation (AO) was +0.707 today. Based on sensitivity analysis applied to the latest guidance, there is an implied 83% probability that New York City will have a cooler than normal November (1991-2020 normal). November will likely finish with a mean temperature near 46.6° (1.4° below normal). Supplemental Information: The projected mean would be 1.1° below the 1981-2010 normal monthly value.

A number of boundary conditions e.g., SSTAs, and teleconnections this year differ from those in recent La Niña winters that saw extremely low snowfall. None of this guarantees a “big” winter, but it does mean the range of plausible outcomes is perhaps broader than what we’ve seen the last few years.

Interesting. You should ask it to follow up with links to related scientific papers on which its assessment was based.

Yes. That’s true.

He’s probably right regarding social media. But it has been discussed fairly widely here.

Yes. There were near misses.

The probabilistic maps from the latest CFSv2 monthly forecasts (just outside its skillful range) appear to be consistent with my baseline thinking (Upper Midwest/Great Lakes-focused cold that spreads eastward, above normal snowfall in the Upper Midwest-Great Lakes Region ( including Chicago to Toronto). Finally, there continues to be no evidence of the kind of buildup of expansive severe cold in the Northern Hemisphere that would produce a severely cold December in the CONUS. This does not preclude the possibility of 1-2 Arctic outbreaks, but those are synoptic events that can't be forecast from this far out. But the path toward an extremely cold month is one that is statistically very unlikely and for which there is no evidence currently to support such claims. Therefore, the Social Media chatter toward that end is pure speculation. The idea that December would rival 1983 is nonsensical. December 1983 (CONUS mean temperature of 25.48°) was the coldest December on record in the CONUS. The last December with a CONUS mean temperature below 30° was December 2009 (29.64°) and that outcome was made possible by extraordinary and persistent blocking in the WPO/EPO/AO domains. Both those frigid Decembers were preceded by Novembers with a much larger deep cold pool in the Northern Hemisphere. So, a logical question would be how such cold would materialize if the deep cold pool is small and there is no indication of 2009-style extreme blocking on the guidance (which can't reliably be forecast from this far out)? If the ingredients aren't present or can't yet be determined to be present, one can't credibly call for such outcomes, especially when they are rare statistical events. Finally, the odds are further tilted against such an outcome by the warming that has occurred in the Northern Hemisphere (especially the Arctic) since 1983. Below are the GISS Arctic region temperature anomalies since 1980.

Simon is highly credible with deep expertise. He doesn't make outlandish statements for clicks or subscriptions. He has done important research. I am aware of his concerns and take them seriously. With regard to the upcoming SSWE, I have outlined what is my current baseline thinking. Overall, I have three general scenarios: Scenario 1: Great Lakes Focused Cold, East Gets a Window (EPO-/AO-/PNA-) -- My Baseline Scenario 2: Colder/Blockier; Classic Eastern Winter Period (EPO-/AO-/PNA+) Scenario 3: Delayed or Short Impact/Persistent SE Ridge; Cold Underperforms in the East; reduced snow opportunities in the Mid-Atlantic Region (EPO-/AO+/PNA-) Under my current baseline, cold would first move into the Great Lakes Region and then spread farther east (except for the Southeast; the cold will be fleeting there). The late November cold shot is unrelated to the stratospheric event. Should the forecast AO- break down relatively quickly, the odds of Scenario 3 would increase. Given guidance skill (lack thereof) at long timeframes, I am sticking with the baseline until there is credible evidence it is going off track. Interestingly, during Winter 1996-1997, January was the coldest month relative to normal for such cities as Detroit and New York. That outcome was suggested by my final winter analog set.

It will turn milder tomorrow. Once in place, the generally milder than normal pattern will likely continue into the closing days of November. However, exceptional warmth appears unlikely. The closing days of November could turn cooler. Meanwhile, today will be Central Park's 1,391st consecutive day without daily snowfall of 4" or more. The record of 1,394 days was set during February 22, 1929 through December 16, 1932. That stretch ended with 6.7" daily snowfall on December 17, 1932. The ENSO Region 1+2 anomaly was -0.7°C and the Region 3.4 anomaly was -0.7°C for the week centered around November 12. For the past six weeks, the ENSO Region 1+2 anomaly has averaged -0.16°C and the ENSO Region 3.4 anomaly has averaged -0.65°C. La Niña conditions will likely continue through at least mid-winter. The SOI was +31.43 today. The preliminary Arctic Oscillation (AO) was -0.316 today. Based on sensitivity analysis applied to the latest guidance, there is an implied 78% probability that New York City will have a cooler than normal November (1991-2020 normal). November will likely finish with a mean temperature near 46.9° (1.1° below normal). Supplemental Information: The projected mean would be 0.8° below the 1981-2010 normal monthly value.

It's something we should be watching closely. The SSWE is imminent. Considering a typical 10-30-day lag, I suspect that the December 10-25 period might see the coldest anomalies relative to normal for such cities as Chicago, New York, and Philadelphia. That's still far out and we'll have to see how things evolve (does the PV split, where do the twin vortices wind up, etc.).

Yes. Since 2020, Pittsburgh has had 7 such days while New York City has had 6. Temperatures have not warmed so sharply and abruptly that such storms are precluded. I suspect that this winter will see at least one such day in both cities. It should also be noted that New York City has gone through two long stretches where 4" or above snow days were infrequent.

There have been some subtle shifts in the guidance. The combination of subtle shifts and long timeframes can lead to big changes. But the timeframe involved is speculative and skill scores at that timeframe are essentially non-existent. What remains extremely likely is that a sudden stratospheric warming event (SSWE) is imminent. Zonal winds will slacken dramatically during the next 5-7 days. A full reversal can't be ruled out. There is typically a lag of 10-30 days for the impact of an SSWE to propagate to the troposphere. So, even as a cold shot appears increasingly likely from the Great Lakes Region to the Northeast to close November, that cold shot will almost certainly not be the result of the imminent SSWE. What happens with the polar vortex (split and location of the pieces) will be crucial. For now, things still appear on a path toward an EPO-/WPO-/AO-/PNA- pattern development. Initially the most significant cold appears likely to dump into the Plains States before pushing eastward. The Great Lakes Region still seems primed for a possible multi-week period of below normal temperatures coupled with above normal precipitation. That should lead to an increase in snowfall totals in such cities as Chicago, Detroit, Windsor, and Toronto. Pieces of the cold should begin to bleed into the East, but perhaps after the first 7-10 days of December. If things evolve along this baseline scenario, the December 10-25 period might see the coldest anomalies relative to normal for such cities as Chicago, New York, Philadelphia. The Southeast could see some intrusions of cold, but the PNA- could promote an unwelcome and persistent tendency for SE ridging. Newer guidance suggests an increased probability of a negative NAO, so that could flatten the SE ridge at times. This is my baseline thinking. IMO, the Week 3-4 CPC Outlooks capture the temperature idea of kind of pattern I expect to prevail during the first half of December. Despite social media chatter 1983-style Arctic outbreaks, a lot would need to change for such an outbreak to become likely. Currently, the Northern Hemisphere's cold pool is much smaller than it was at this time in 1983: 2025: 1983: In the very long range, some of the subtle shifts in the teleconnections e.g., dissipation of the WPO-, could translate into the trough's migrating back to the West and a Southeast Ridge reviving in the closing week of December. That's not shown on the weekly ECMWF guidance. But the December 22-29 period's 500 mb forecasts should be monitored for hints of change. It should be noted that neither the MJO nor teleconnections can be forecast with skill at such a forecast horizon. In sum, wintry opportunities should increase in December, first in Plains States and Great Lakes and then farther East. The Great Lakes Region and Ohio Valley look primed for above normal snowfall during December. The Southeast could have the most difficult time seeing the cold try to gain traction, but some cold shots should eventually break through. The closing week of December looks uncertain. Much depends on how the SSWE's impacts will evolve and other variables that cannot be forecast with skill at that range. Typical SSWE lags would argue that the breakdown in the pattern might occur later. Then there's always the wild card of additional warming events.

I used the NE as an example, because it seemed that a lot of the commentary had been focused on the NE U.S.

Below normal temperatures will prevail through tomorrow. Highs will be mainly in the middle and upper 40s in New York City with lows in the middle and upper 30s. A milder pattern will then develop afterward. Some rain or rain showers are possible. Once in place, the milder pattern will likely continue into the closing days of November. However, exceptional warmth appears unlikely. The closing days of November could turn cooler. Meanwhile, today will be Central Park's 1,390th consecutive day without daily snowfall of 4" or more. The record of 1,394 days was set during February 22, 1929 through December 16, 1932. That stretch ended with 6.7" daily snowfall on December 17, 1932. The ENSO Region 1+2 anomaly was -0.7°C and the Region 3.4 anomaly was -0.7°C for the week centered around November 12. For the past six weeks, the ENSO Region 1+2 anomaly has averaged -0.16°C and the ENSO Region 3.4 anomaly has averaged -0.65°C. La Niña conditions will likely continue through at least mid-winter. The SOI was +38.30 today. That is the highest SOI value since December 23, 2022 when the SOI reached +50.96. The preliminary Arctic Oscillation (AO) was -1.027 today. Based on sensitivity analysis applied to the latest guidance, there is an implied 74% probability that New York City will have a cooler than normal November (1991-2020 normal). November will likely finish with a mean temperature near 47.1° (0.9° below normal). Supplemental Information: The projected mean would be 0.6° below the 1981-2010 normal monthly value.

The idea of an imminent SSW/MSW event is a high-confidence one. However, there is often a tendency to treat forecast developments (“SSW → PV split → EPO-/WPO-/AO-/PNA- → brutal NE weather”) as if it were an inevitable, linear, cause-and-effect chain. If such logic were reliable, forecasting accuracy at multi-week stages would be high. That isn't the case. I personally believe that there will be an increase in wintry effects, especially from near mid-December into at least late December based on typical 1-3 week lags and the currently forecast teleconnection evolution. That's my baseline thinking at present. However, that thinking isn't cast in stone. Reality is messier. For example, not every SSW leads to a prolonged deep AO-. Not every AO- period results in severe cold and/or excessive snowfall. From this far out, model skill is poor to non-existent on critical synoptic factors e.g., future storm tracks, the emergence of North Pacific jet streaks, exact ridge-trough placement, etc. A bad pattern coupled with a well-timed phase can produce a big snowstorm; a great pattern but badly-timed phases or absence of shortwaves can result in a lack of snowfall. Seemingly favorable ensemble means can also disguise large differences among ensemble members. Clusters can provide insight into some scenarios. Here are the forecast 500 mb anomalies at 360 hours: Here are the latest 500 mb and 1000 mb ECMWF clusters: 500 mb: 1000 mb: For now, potential is on the table. But nothing is locked in, just yet, in terms of specific details.

A weak system could bring a few scattered rain and/or snow showers tonight into tomorrow. No measurable snowfall is likely in New York City. Since daily snowfall and temperature records were kept, just 1 out of 55 (1.8%) systems with minimum temperatures of 38° or above had measurable snowfall in Central Park. Afterward, tomorrow will be another cool day with highs topping out in the 40s. Below normal temperatures will prevail through at least Thursday. Highs will be mainly in the middle and upper 40s in New York City with lows in the middle and upper 30s. A milder pattern will likely develop during the latter part of the week. Some rain or rain showers are possible. Once in place, the milder pattern could continue for a week or longer. Meanwhile, today will be Central Park's 1,389th consecutive day without daily snowfall of 4" or more. The record of 1,394 days was set during February 22, 1929 through December 16, 1932. That stretch ended with 6.7" daily snowfall on December 17, 1932. The ENSO Region 1+2 anomaly was -0.7°C and the Region 3.4 anomaly was -0.7°C for the week centered around November 12. For the past six weeks, the ENSO Region 1+2 anomaly has averaged -0.16°C and the ENSO Region 3.4 anomaly has averaged -0.65°C. La Niña conditions will likely continue through at least mid-winter. The SOI was +27.87 today. The preliminary Arctic Oscillation (AO) was -1.686 today. Based on sensitivity analysis applied to the latest guidance, there is an implied 61% probability that New York City will have a cooler than normal November (1991-2020 normal). November will likely finish with a mean temperature near 47.4° (0.6° below normal). Supplemental Information: The projected mean would be 0.3° below the 1981-2010 normal monthly value.

I'm well. I hope you're doing well. Hopefully, this coming winter will produce a lot of snowy days. It would be nice to turn back the clock to the kind of winters that made this site grow.

The Earth would typically need to see a shift of 0.1° (about 7 miles) or more for an impact on its climate through changes in solar insolation. The reported shift is far less than that. It's essentially meaningless from a climate standpoint.

The following morning:

Tomorrow will be another cool day with highs topping out in the 40s. Below normal temperatures will prevail through at least Wednesday and possibly Thursday. Highs will be mainly in the middle and upper 40s in New York City with lows in the middle and upper 30s. A milder pattern will likely develop during the latter part of the week. Some rain or rain showers are possible. Once in place, the milder pattern could continue for a week or longer. Meanwhile, today will be Central Park's 1,388th consecutive day without daily snowfall of 4" or more. The record of 1,394 days was set during February 22, 1929 through December 16, 1932. That stretch ended with 6.7" daily snowfall on December 17, 1932. The ENSO Region 1+2 anomaly was -0.7°C and the Region 3.4 anomaly was -0.7°C for the week centered around November 12. For the past six weeks, the ENSO Region 1+2 anomaly has averaged -0.16°C and the ENSO Region 3.4 anomaly has averaged -0.65°C. La Niña conditions will likely continue through at least mid-winter. The SOI was +19.47 today. The preliminary Arctic Oscillation (AO) was -2.297 today. Based on sensitivity analysis applied to the latest guidance, there is an implied 62% probability that New York City will have a cooler than normal November (1991-2020 normal). November will likely finish with a mean temperature near 47.5° (0.5° below normal). Supplemental Information: The projected mean would be 0.2° below the 1981-2010 normal monthly value.