donsutherland1

March 1-2, 1980 might have an intellectual property claim against the AIFS.

Through tomorrow, highs will generally reach the 40s during the daytime and 30s for lows in New York City. Some light precipitation is possible tomorrow evening into Thursday. Rain showers could transition to a period of snow or snow showers, especially well north and west of New York City where a light accumulation is possible. Afterward, temperatures will "step down" with highs mainly in the middle and upper 30s in New York City and lows in the lower and middle 20s. Some teens are likely outside of New York City. Flurries and perhaps a heavier snow shower are possible on Saturday and Sunday as a renewed flow of cold air moves across the region. Temperatures will remain below normal through at least early next week. After January 20th, conditions might become more favorable for both cold and snowfall, especially if the PNA remains predominantly positive, as has often occurred following the breakdown of long-duration PNA- regimes. PNA-related developments would have larger implications for snowfall. A persistently positive PNA would have above climatological risk of moderate or significant snowfalls. A mainly negative PNA would favor mainly small snowfalls. It will likely be another day or two before the guidance reaches the high-skill timeframe for teleconnection forecasts related to closing days of January. The ENSO Region 1+2 anomaly was -0.7°C and the Region 3.4 anomaly was -0.8°C for the week centered around January 7. For the past six weeks, the ENSO Region 1+2 anomaly has averaged -0.47°C and the ENSO Region 3.4 anomaly has averaged -0.67°C. La Niña conditions will likely continue into at least late winter. The SOI was +8.91 today. The preliminary Arctic Oscillation (AO) was -0.667 today. Based on sensitivity analysis applied to the latest guidance, there is an implied near 58% probability that New York City will have a cooler than normal January (1991-2020 normal). January will likely finish with a mean temperature near 33.3° (-0.4° below normal). Supplemental Information: The projected mean would be 0.7° above the 1981-2010 normal monthly value.

Historically, about 30% of winters with similar or less snowfall than 2025-2026 through January 12th went on to see 25" or more snow. My thinking coming into this winter was 15"-25". I still think that's realistic. In any case, here's the historical data for Central Park.

Here's how New York City has fared when it has had less than 8" of seasonal snowfall through January 12th (n=88 cases). The 2025-2026 figure through January 12th is 7.7".

This morning's preliminary value of the PNA was +0.707. That's the highest the PNA has been since November 20, 2025 when the PNA reached +0.738. The PNA will remain positive for several more days before it is forecast to go somewhat negative for a short period of time. Afterward, the GEFS show the PNA rebounding. It remains plausible that a regime change (20+ days where the PNA>0 during the January 12-February 11 period or the 30-day period following the end of the recent long-duration PNA- regime) can occur. If so, perhaps the best opportunity for a moderate or larger snowstorm in the Middle Atlantic Region or Northeast could be in the January 25-February 15 timeframe. For such potential to be realized, the synoptic pieces would need to become available. So far, the subtropical jet has been largely quiet this winter. Should the forecast strong WWB materialize, that could lead to the subtropical jet's becoming more active across the southern tier of the U.S. some 10-14 days later. Whether that would align during a favorable longwave pattern remains to be seen. In the near-term, lighter snows are likely in parts of the Great Lakes Region and Northeast. The lake effect belts could see greater snowfalls, especially as Arctic air could try to get involved next week.

I have a list of Southeast Region snowstorms and just checked the dates last night. The date range is where the Southeast was receiving snow.

Yes, the PNA is far more important to Atlanta's January snowstorms than the NAO. Since 1950, the PNA was positive for 84.2% of Atlanta's 1" or greater snowstorms. The NAO was negative for 63.2% of such storms.

Bridgeport, Islip, Central Park, JFK Airport, LaGuardia Airport, and White Plains all had highs of 41F (5.0C) today. If that holds, it would be the first time since November 21, 1998 that all six locations had identical high temperatures.

Through Wednesday, highs will generally reach the 40s during the daytime and 30s for lows in New York City. Somewhat colder readings are likely outside the City and in areas where strong radiational cooling takes place. After the middle of next week, temperatures will "step down" with highs mainly in the middle and upper 30s in New York City and lows in the middle and upper 20s. Some light precipitation is possible on Friday. Rain showers could transition to a period of snow. A light accumulation is possible. Some additional precipitation could arrive on Sunday. No significant Arctic blasts or significant snowfalls are likely through at least mid-January. Afterward, conditions might become more favorable for both cold and snowfall, especially if the PNA remains predominantly positive, as has often occurred following the breakdown of long-duration PNA- regimes. PNA-related developments would have larger implications for snowfall. A persistently positive PNA would have above climatological risk of moderate or significant snowfalls. A mainly negative PNA would favor mainly small snowfalls. It will likely be another day or two before the guidance reaches the high-skill timeframe for teleconnection forecasts. The ENSO Region 1+2 anomaly was -0.7°C and the Region 3.4 anomaly was -0.8°C for the week centered around January 7. For the past six weeks, the ENSO Region 1+2 anomaly has averaged -0.47°C and the ENSO Region 3.4 anomaly has averaged -0.67°C. La Niña conditions will likely continue into at least late winter. The SOI was +12.16 today. The preliminary Arctic Oscillation (AO) was -1.040 today. Based on sensitivity analysis applied to the latest guidance, there is an implied near 55% probability that New York City will have a cooler than normal January (1991-2020 normal). January will likely finish with a mean temperature near 33.5° (-0.2° below normal). Supplemental Information: The projected mean would be 0.9° above the 1981-2010 normal monthly value.

PSV88, Rest assured, I have a thick skin. I don't take it personally. I hope he also remains here, too.

For those who want a highly simplified but easy-to-understand description of sensitivity analysis, one can reference the following: https://thedecisionlab.com/reference-guide/statistics/sensitivity-analysis. And for those who want insight into the estimated probability, applying multiple variations to the model value, assessing the probability against a benchmark (1991-2020 normal value) using a normal distribution.

The January 15-16 event was highly unlikely to be a big snowstorm from the onset even if some social media accounts warned of a "big one." Aside from occasional operational GFS runs (unsupported by the other guidance and the various ensembles), no big event was on the table. Three important reasons apply: 1) The AO-/PNA+ pattern is just getting established. The trough was not likely to be sufficiently sharp for January 15-16. 2) There are numerous areas of vorticity competing with one another. The probability that the various areas of vorticity will develop into a single consolidated low that takes an ideal track for a classic NE snowstorm is low. Large splashes of color on vorticity maps don't always translate into surface potential. Neither do deep 500 mb lows. There's a lot involved for the upper levels and surface to become aligned. 3) The realistic scenarios of a light impact had been available for some time, even as the exact solution was outside the range of the guidance regarding the ability to resolve synoptic details. During the 1/11 0z EPS cycle, a single ensemble member had 6"+ snow (none had 10"+) and during the 1/11 12z EPS cycle, no ensemble members had 6"+ snowfall in New York City. For Boston, the figures were 6 and 4 members respectively. Bottom line: the probability of a significant NE snowstorm was low; the probability of a major NE snowstorm was extremely low. Based on the above three reasons, I never incorporated the idea of a significant or major snowstorm into my daily posts regarding the January 15-16 timeframe. If one is constructing a checklist, one needs both a favorable pattern and favorable synoptic details to get a KU-type snowstorm. If either is lacking, the probability of such an outcome is low. When both are lacking (as is the case regarding January 15-16), the odds are close to zero.

For those who are not familiar with it, sensitivity analysis incorporates uncertainty into an assessment. It is not deterministic in nature. It is not a point estimate. After the first 11 days of the month, the probability of a colder than normal January was just 55%. That means that there is still a lot of uncertainty. One sees it in the varying ensembles and weeklies and the lack of run-to-run continuity in cases. That's the key takeaway from any sensitivity analysis. It's capturing the large amount of uncertainty quite well, assuming one knows what one is looking at with the probabilities. For perspective, back in December, the estimated probability of a below normal monthly anomaly was 89% on December 7th. That was about as close to a "slam dunk" as one can get at such a long lead time. The estimated monthly mean temperature then was 34.0° (December finished at 33.8°). The major weakness is that the analysis assumes a Gaussian curve (normal distribution). Not everything is normally distributed. This assumption is necessary, because the kind of detailed model verification data that would be needed to construct a more robust curve is not publicly available. Thus, the simplifying assumption of a normal distribution is used. Finally, I include the estimated monthly mean temperature only because it's nice to have. But one should know what one is looking at. The estimated mean is similar to an ensemble mean, while the probability of an outcome plays the role akin to an ensemble spread (low probability reflects a large spread in outcomes due to high uncertainty). IMO, the probability of an outcome (I just use below or above normal) is really the more useful element of the piece concerning sensitivity analysis, especially at long lead times.

After 34 consecutive days during which it was negative, the PNA went positive today (+0.173). Whether a persistent PNA+ regime develops will have important medium- and long-range implications. Following this evenings snow squall and snow showers, modestly cooler air is returning to the region. Through midweek, highs will generally reach the 40s during the daytime and 30s for lows in New York City. Somewhat colder readings are likely outside the City and in areas where strong radiational cooling takes place. After the middle of next week, temperatures will "step down" with highs mainly in the middle and upper 30s in New York City and lows in the middle and upper 20s. Some light precipitation is possible on Friday. Rain showers could transition to a period of snow. A light accumulation is possible. Additional precipitation could arrive on Sunday. No significant Arctic blasts or significant snowfalls are likely through at least mid-January. Afterward, conditions might become more favorable for both cold and snowfall, especially if the PNA remains predominantly positive, as has often occurred following the breakdown of long-duration PNA- regimes. PNA-related developments would have larger implications for snowfall. A persistently positive PNA would have above climatological risk of moderate or significant snowfalls. A mainly negative PNA would favor mainly small snowfalls. It will likely be another day or two before the guidance reaches the high-skill timeframe for teleconnection forecasts. The ENSO Region 1+2 anomaly was -0.7°C and the Region 3.4 anomaly was -0.5°C for the week centered around December 31. For the past six weeks, the ENSO Region 1+2 anomaly has averaged -0.37°C and the ENSO Region 3.4 anomaly has averaged -0.63°C. La Niña conditions will likely continue into at least late winter. The SOI was +20.69 today. The preliminary Arctic Oscillation (AO) was -1.499 today. Based on sensitivity analysis applied to the latest guidance, there is an implied near 55% probability that New York City will have a cooler than normal January (1991-2020 normal). January will likely finish with a mean temperature near 33.5° (-0.2° below normal). Supplemental Information: The projected mean would be 0.9° above the 1981-2010 normal monthly value.

Three photos from Armonk during this evening's snow squall and a short video: