donsutherland1

So far, things have gone pretty much as expected in December. The December 1-10 idea is verifying. The big question concerning late December is whether the WPO- will weaken allowing unfavorable teleconnections to reshape the pattern. That is a possibility, but isn't certain. Other possibilities also exist.

Statistical tidbit from 1990-91 through 2024-25: 14/15 (93%) of winters with above normal seasonal snowfall had a least one day with 8" or more snow (72% prior to 1990-91) 17/18 (94%) of winters with below normal seasonal snowfall did not have any 8" or above daily amounts (75% prior to 1990-91) 14/17 (82%) of winters with at least one day with 8" or above snowfall had above normal seasonal snowfall (63% prior to 1990-91) 2014-15 with 50.3" seasonal snowfall was the lone exception for seasons with above normal snowfall with a maximum daily amount of 7.5" since 1990-91. This data suggests that in the contemporary warmer climate, a big snowstorm has become relatively more important to seasonal snowfall outcomes than in the past. Both subsets are longer than 30 seasons in length suggesting that the difference provides some insight. Moreover, this is what would be expected in a warmer climate with somewhat fewer snowy days.

Below is why a relaxation is possible during December 20-31. The WPO is forecast to become less negative while a PNA-, EPO+,AO+, NAO+ regime is largely in place. The WPO would no longer be sufficiently negative to offset the impact of unfavorable teleconnections. Fortunately, that's still far out where skill is low, so it's a plausible but not yet certain outcome.

Do the best you can during these difficult times. Don’t lose hope. Both of you are in my thoughts and prayers.

A fresh surge of cold air will arrive tonight. Tomorrow will likely see subfreezing temperatures across much of the region and Tuesday morning could rival or even surpass the cold of December 5th at some locations. The ongoing stretch of below normal temperatures will likely continue into or through the second week of December. December 1-10 will be a solidly colder than normal period. The potential exists for the coldest first 10 days of December since at least 2007 (33.4°, 5th coldest December 1-10 since 2000). The five coldest December 1-10 periods since 2000 were: 1. 30.6°, 2002 2. 32.2°, 2003 3. 32.4°, 2000 4. 33.1°, 2005 5. 33.4°, 2007 All 5 of these cases had measurable snowfall in Central Park. The WPO is forecast to become strongly negative beyond December 10th. That would likely contribute to the December 10-20 period also being colder to perhaps much colder than normal overall. The probability that December 2025 will have a maximum monthly temperature below 60° is increasing. The last time that happened was in 2019 when the monthly high was 58°. If 2025 has a monthly high below 60°, that would be only the fifth such occurrence since 2000 (2003, 2004, 2005, and 2019 are the cases since 2000). The ENSO Region 1+2 anomaly was -0.1°C and the Region 3.4 anomaly was -0.6°C for the week centered around November 26. For the past six weeks, the ENSO Region 1+2 anomaly has averaged -0.18°C and the ENSO Region 3.4 anomaly has averaged -0.67°C. La Niña conditions will likely continue through at least mid-winter. The SOI was -7.11 today. The preliminary Arctic Oscillation (AO) was -2.202 today. Based on sensitivity analysis applied to the latest guidance, there is an implied near 89% probability that New York City will have a cooler than normal December (1991-2020 normal). December will likely finish with a mean temperature near 34.0° (5.1° below normal). Supplemental Information: The projected mean would be 3.5° below the 1981-2010 normal monthly value.

Here's the data for Boston:

If the WPO relaxes from its forecast values of -2.000 or below, other teleconnections can gain influence over the pattern. The EPS currently forecasts an EPO+/AO+/PNA-/NAO+ regime toward the end of its run. If the WPO rises, that could allow ridging to expand across the CONUS with warmth following after a few days lag. December 30-31, 1999: The December 30-31, 1999 composite 500 mb map is one example of how unfavorable teleconnections overwhelmed a weaker WPO-. Then, the WPO was still impressive (below -1.000) but it was not at the extreme values necessary to overwhelm the pattern. Milder conditions rapidly spread into the East. Despite much above normal temperatures to start January 2000, the month wound up colder than normal. Late January (January 24-27 timeframe) saw a major snowstorm in the Southeast and lower Mid-Atlantic region. For now, it looks to remain generally colder than normal through around December 20th. Nothing is cast in stone for the remainder of the month, though some temporary relaxation is plausible. IMO, the odds remain against a complete breakdown of the pattern and the onset of a sustained warm pattern during the closing 10-11 days of December. Still, it's worth watching the evolution of the guidance. I suspect that there could be an increased risk of a pattern breakdown after mid-January, which often happens during La Niña winters, but that's in the speculative range right now. The PNA could play a larger role in how January evolves.

The Department of Sanitation was in its own insular bubble that day with no idea of the imminent storm, even as Philadelphia was seeing 1/4-mile visibilities for hours. Maybe they could have followed observations here and learned about the snow.

This morning's snowfall totals: Bridgeport: Trace Central Park: Trace LaGuardia Airport: Trace Newark: 0.1"

Parts of the region received dustings and even coatings from bursts of light snow that fell overnight into the early morning due to pockets of instability. Newark picked up 0.1". The weekend will end on an unseasonably cool note. A fresh surge of cold air will arrive tomorrow night. Monday will likely see subfreezing temperatures across much of the region and Tuesday morning could rival or even surpass the cold of December 5th. The ongoing stretch of below normal temperatures will likely continue into or through the second week of December. December 1-10 will be a solidly colder than normal period. The potential exists for the coldest first 10 days of December since at least 2007 (33.4°, 5th coldest December 1-10 since 2000). The five coldest December 1-10 periods since 2000 were: 1. 30.6°, 2002 2. 32.2°, 2003 3. 32.4°, 2000 4. 33.1°, 2005 5. 33.4°, 2007 All 5 of these cases had measurable snowfall in Central Park. The WPO is forecast to become strongly negative beyond December 10th. That would likely contribute to the December 10-20 period also being colder to perhaps much colder than normal. The probability that December 2025 will have a maximum monthly temperature below 60° is increasing. The last time that happened was in 2019 when the monthly high was 58°. If 2025 has a monthly high below 60°, that would be only the fifth such occurrence since 2000 (2003, 2004, 2005, and 2019 are the cases since 2000). The ENSO Region 1+2 anomaly was -0.1°C and the Region 3.4 anomaly was -0.6°C for the week centered around November 26. For the past six weeks, the ENSO Region 1+2 anomaly has averaged -0.18°C and the ENSO Region 3.4 anomaly has averaged -0.67°C. La Niña conditions will likely continue through at least mid-winter. The SOI was -23.41 today. The preliminary Arctic Oscillation (AO) was -1.756 today.

My comment regarding snowfall only goes through December 20th. I think if things grow more favorable for the East Coast, it would be during the December 20-31 period as things stand now. Things can still change beforehand, because teleconnections forecasts lose skill beyond 10-14 days.

Today's PNA value was -0.355 with five of the first six days of December seeing negative values. The forecast calls for a continuation of the negative PNA: Nevertheless, the WPO is forecast to dive to below -2.000 on the EPS and to -3.000 or below on the GEFS. As a result, a foundation is being laid for much of eastern North America to wind up colder to perhaps even much colder than normal during the December 11-20 period. This pattern would tend to focus the snows on the Great Lakes region while the East Coast sees lesser snows. PNA- setups typically favor lighter snows on the East Coast. The single exception during December since 1980 was the Boxing Day Blizzard of 2010. Such strongly negative WPO cases also see warmer than normal conditions in the Southwest.

I haven't seen any messages as of now.

Some brief periods of light snow produced a dusting in Larchmont in southern Westchester County.

Washington, D.C.'s distribution of December days with measurable snowfall and the highest daily amount for each date. Highest percentage of 1" or above amounts: December 10 5.7% days (8 cases) Highest percentage of 6" or above amounts: December 24 1.4% days (2 cases)