donsutherland1

Thanks. I thought I had loaded the CLE local storm reports, but didn’t.

So far, the ideas expressed last Sunday remain in good shape. 1. The first half of December continues to look cold with a weekly anomaly of 6°-10° below normal likely during that period. In fact, New York City could have its coldest December 1-10 period since 2002. 2. A significant lake effect snow event is underway. Several locations have seen excessive lake effect snow so far. Cassadaga, NY (31.6") and Mayville, NY (30.0") have the highest amounts so far. Buffalo has received a trace of snow, but as the lake effect snow bands move northward today, accumulating snow is likely there. Chicago (2.9"), Detroit (1.7"), and Toronto (0.2 cm) have all seen measurable snow. No measurable snow has fallen in Boston, New York City, or Philadelphia. 3. The potential for a colder than normal December has increased in parts of the eastern third of the U.S. Since 1980, all four cases where New York City had a mean temperature of 36.5° or below, wound up having a colder than normal December. The latest guidance shows New York City with a December 1-10 mean temperature near 32.5°. The outcome farther west in such cties as Chicago, Detroit, and Indianapolis remains less certain and will depend on the timing of the pattern change. The farther east one is, the more likely that the month will come out with a colder anomaly. 4. The CFSv2 is pushing a warmup around mid-month. The November 29 12z ECMWF weeklies are holding it off for an additional week. As noted previously, the guidance has tended to rush the timing of pattern changes. Four thoughts going forward: 1. The EPO is forecast to head toward neutral levels toward mid-month. The AO and PNA are also forecast to head toward neutral levels. Therefore, a pattern change seems likely, but probably with a lag that could favor the timing shown on the ECMWF weeklies. 2. Even as the pattern in the East is likely to be dry for much of the first week of December, a clipper system could bring some light snow or flurries to the northern Mid-Atlantic/southern New England areas late Tuesday night and Wednesday. Boston might have a chance to pick up an inch of snow. Philadelphia and possibly New York City might only see some flurries. 3. Following the clipper, the coldest air so far this season will move into the eastern third of the U.S. 4. Out West, British Columbia could see a period of near record and record warmth develop for Tuesday through Thursday (December 3-5). Overall, the exceptional warmth in BC and the cold in the East showed up quite well on the November 29 12z ECMWF Weeklies.

DCA _ NYC _ BOS __ ORD _ ATL _ IAH __ DEN _ PHX _ SEA 0.0 -0.5 -0.3 1.2 0.2 1.7 3.6 3.6 4.4 DCA _ NYC _ BOS __ ORD _ DTW _ BuF __ DEN _ SEA _ BTV 8.0 16.5 35.0 40.0 45.0 95.0 55.0 8.0 75.0

Enjoy them. Yes, growing season will be ending now. I hope you had a great Thanksgiving Day.

A colder regime is now settling into place and will likely persist through at least mid-December. There will be some sprinkles or flurries this evening. Afterward, the skies wil clear. New York City's Central Park will very likely experience its first freeze of the season tomorrow morning. The average first freeze occurs on November 21st. That's 10 days later than the 1961-1990 average. On account of successive waves of cold, the first two weeks of December will likely feature mainly below normal temperatures. The long-range guidance remains in good agreement for a cold first half of December. Significant lake effect snow is likely. At least through much of the first week of December, precipitation will likely be below to much below normal in the region. 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 +0.8°C and the Region 3.4 anomaly was -0.1°C for the week centered around November 20. For the past six weeks, the ENSO Region 1+2 anomaly has averaged 0.00°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. The SOI was +6.49 today. The preliminary Arctic Oscillation (AO) was -1.544 today. Based on sensitivity analysis applied to the latest guidance, there is an implied near 100% probability that New York City will have a warmer than normal November (1991-2020 normal). November will likely finish with a mean temperature near 51.4° (3.4° above normal). November 2024 will be the third November since 2020 with a monthly mean temperature of 50° or above. In addition, Fall 2024 will likely finish with a seasonal mean temperature of 60.4°. That would tie Fall 2017 for the 6th warmest Fall on record.

I run the sensitivity analysis daily. The AO and SOI values are usually available each day.

The storm responsible for today's rain is now moving away from the region. In its wake, noticeably colder air will begin to move into the region. Below normal temperatures are likely for the remainder of November. On account of successive waves of cold, the first two weeks of December will likely feature mainly below normal temperatures. The long-range guidance remains in good agreement for a cold first half of December. Significant lake effect snow is likely. At least through much of the first week of December, precipitation will likely be below to much below normal in the region. 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 +0.8°C and the Region 3.4 anomaly was -0.1°C for the week centered around November 20. For the past six weeks, the ENSO Region 1+2 anomaly has averaged 0.00°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. The SOI was +19.91 today. The preliminary Arctic Oscillation (AO) was -1.196 today. Based on sensitivity analysis applied to the latest guidance, there is an implied near 100% probability that New York City will have a warmer than normal November (1991-2020 normal). November will likely finish with a mean temperature near 51.4° (3.4° above normal). November 2024 will be the third November since 2020 with a monthly mean temperature of 50° or above.

December 1-10 will very likely have a mean temperature below 40° (likely in the 37.5°-38.5° range based on the guidance). The Week 4 CFSv2 shows much above normal temperatures for the week that ends with Hanukkah and Christmas. Here's how NYC has fared since 1980 for following various mean temperatures for the December 1-10 period: Considering that 76% of cases following the December 1-10 value have averaged either below 35° or 40° or above for the December 25 +/-3 days period, the odds are probably tilted toward the latter given the CFSv2 forecast and EPS weeklies. The first half of December and possibly first three weeks could have a cold anomaly before the pattern breaks.

A cooler pattern is now in its early stages of developing. Rain will arrive late tonight. The rain will continue into tomorrow night. Some of the distant northern and western suburbs could see some snow mix in. A general 0.50"-1.00" rainfall is likely. Colder air will begin to move into the region following the Thanksgiving Day storm. On account of successive waves of cold, the first two weeks of December will likely feature mainly below normal temperatures. The long-range guidance remains in good agreement for a cold first half of December. Significant lake effect snow is likely. 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 +0.8°C and the Region 3.4 anomaly was -0.1°C for the week centered around November 20. For the past six weeks, the ENSO Region 1+2 anomaly has averaged 0.00°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. The SOI was +21.06 today. The preliminary Arctic Oscillation (AO) was +0.187 today. Based on sensitivity analysis applied to the latest guidance, there is an implied near 100% probability that New York City will have a warmer than normal November (1991-2020 normal). November will likely finish with a mean temperature near 51.4° (3.4° above normal). November 2024 will be the third November since 2020 with a monthly mean temperature of 50° or above.

In theory, yes. But a lot would have to happen for such a pattern to actually develop.

A cooler pattern is now imminent. It will turn cooler and increasingly cloudy tomorrow. Rain will arrive late tomorrow night or Thursday morning. The rain will continue into Thursday night. Distant northern and western suburbs could see some snow mix in. Colder air will begin to move into the region following the Thanksgiving Day storm. On account of successive waves of cold, the first two weeks of December will likely feature mainly below normal temperatures. The long-range guidance is in good agreement for a cold first half of December. Significant lake effect snow is 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 +0.8°C and the Region 3.4 anomaly was -0.1°C for the week centered around November 20. For the past six weeks, the ENSO Region 1+2 anomaly has averaged 0.00°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. The SOI was +24.37 today. The preliminary Arctic Oscillation (AO) was +1.555 today. Based on sensitivity analysis applied to the latest guidance, there is an implied near 100% probability that New York City will have a warmer than normal November (1991-2020 normal). November will likely finish with a mean temperature near 51.2° (3.2° above normal).

It was a cold winter. The highlight was late December into early January, which featured extreme cold. NYC saw the temperature fall to -1° on December 25th.

Tomorrow will be the warmest day of the week and likely for some time to come. Temperatures will top out in the middle and perhaps upper 50s, even as showers and a period of rain are likely. A storm will bring additional rain on Thursday into Thursday night. Colder air will begin to move into the region following the Thanksgiving Day storm. On account of successive waves of cold, the first two weeks of December will likely feature mainly below normal temperatures. The long-range guidance is in good agreement for a cold first half of December. Significant lake effect snow is 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 +0.8°C and the Region 3.4 anomaly was -0.1°C for the week centered around November 20. For the past six weeks, the ENSO Region 1+2 anomaly has averaged 0.00°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. The SOI was +17.62 today. The preliminary Arctic Oscillation (AO) was +1.120 today. Based on sensitivity analysis applied to the latest guidance, there is an implied near 100% probability that New York City will have a warmer than normal November (1991-2020 normal). November will likely finish with a mean temperature near 51.0° (3.0° above normal).

I suspect that the strengthening PV and lagged response to the development of an AO+/NAO+ will increase the risk for warming late in December. It will take some time to scour out the cold that will dominate during the first half of the month, especially when the PNA is positive.

I agree with his assessment. The MJO is currently in Phase 3 at a high amplitude. As it moves into and through the Maritime Continent, one would generally expect warmth in the East. The MJO's impact can be offset by other variables.

Even if the two-thirds or so of December is cold, there is no assurance that the pattern would lock in. Indeed, I suspect that it will begin to transition toward a milder pattern around the Solstice. Even very cold Decembers have been followed by generally mild conditions during the rest of the winter.

Currently, 7 of the 9 statistical models and 9 of the 17 dynamical models are forecasting neutral ENSO conditions for the winter. Over the past 6 weeks, the Region 3.4 anomaly has averaged -0.23°C. The latest weekly figure for the week centered around November 20th is -0.1°C.

Tomorrow and Tuesday will be the warmest days of the week and likely for some time to come. Temperatures will top out in the middle and perhaps upper 50s, especially on Tuesday. Afterward colder air will begin to move into the region. On account of successive waves of cold, the first two weeks of December will likely feature mainly below normal temperatures. The long-range guidance is in good agreement for a cold first half of December. Significant lake effect snow is 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 +0.2°C and the Region 3.4 anomaly was 0.0°C for the week centered around November 13. For the past six weeks, the ENSO Region 1+2 anomaly has averaged -0.20°C and the ENSO Region 3.4 anomaly has averaged -0.30°C. Neutral ENSO conditions may evolve into a La Niña event during the late fall. Uncertainty as to whether a La Niña will develop has increased. The SOI was +21.82 today. The preliminary Arctic Oscillation (AO) was +0.130 today. Based on sensitivity analysis applied to the latest guidance, there is an implied near 100% probability that New York City will have a warmer than normal November (1991-2020 normal). November will likely finish with a mean temperature near 50.9° (2.9° above normal).

Five thoughts on the upcoming colder pattern triggered by a developing EPO block and forecast AO-/PNA+ pattern: 1. The first half of December looks cold in much of the East. A one-week period with a temperature anomaly of 6°-10° below normal is plausible. 2. Initially snowfall options could be limited due to the source region of the air masses. It remains to be seen whether the recent rainfall in the East and the upcoming storm to the Great Lakes region later this week were exceptions rather than the beginning of the end of the ongoing drought in the Northeast. Until a persistently wetter pattern emerges, my operating assumption remains that the drought will persist. That raises the bar for big snowfall events even as cold should be sufficient to allow for opportunities through at least the first half of December. The Great Lakes region and LES belts should be in good shape. For snowfall, I'd rather be in such cities as Chicago, Detroit, Buffalo and Toronto than Philadelphia, New York City, or Boston. 3. In most cases following exceptional November warmth and a colder first half of December, the second half of the month was not much warmer than normal. 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. 4. The long-range guidance might rush the break in the colder pattern. I suspect that timing closer to the winter solstice than mid-month might be more realistic for the onset of any pattern change. 5. These developments do not necessarily mean that winter won't be warmer than normal as per the seasonal guidance (the seasonal guidance usually does better with three month assessments than month-to-month ones). They do reinforce the idea that the coming winter won't be as abnormally warm as the last two winters have been. A potential wildcard remains ENSO. The probability of a full-fledged La Niña event (tri-monthly average) has decreased. A neutral-cold outcome remains possible. The relative ENSO Index (RONI) will be consistent with La Niña.

2024 remains on track to become the hottest year on record on all of the major climate data sets. To avoid setting a new record, November 23-December 31 would have to see global temperatures that were last seen in 2000. Climate change played a major role in the exceptional heat in the Sahel region in April, the April-May heat in Asia, the sustained extreme heat in Mexico during May and June, the Mediterranean heatwave in July, and the unprecedented autumn heatwave in the Southwestern United States. The 2024 emissions gap report revealed that the world remains on track for 2.6°C-3.1°C warming by 2100. It's cover pleaded with those who would gather for COP 29, "No more hot air...please!" If one wondered what inaction would look like, one saw it at COP 29. The conference, which featured some late-moment drama, was as close to a total failure as it could have been. Despite spin coming from some quarters that it made at least some progress, the reality is that it made no progress. Instead of agreements, declarations, or binding commitments, nations were urged, called upon or encouraged to act. No mention of fossil fuels, responsible for the climate-warming greenhouse gas pollution, was made in any of the four concluding documents. Instead, in an act of cynicism borrowed from COP 28, "transitional fuels," meaning such fossil fuels as natural gas, were embraced as helpful for the "energy transition." Perhaps in the insular world of COP 29, the participants believe rhetoric alone is sufficient to address problems. Just maybe, they believe that one can simply wish away anthropogenic climate change. Outside COP 29, there is broad consensus that credible goals and commitments are specific and measurable. They come with clear targets to guide progress. The most effective ones come with mechanisms to address gaps, be they cost overruns or production shortfalls, when they arise. None of these attributes made it into any of the four COP 29 documents. If anything, COP 29 delivered the last rites for the Paris Goal of holding warming to no more than 1.5°C. Below is a summary of the failed COP 29 conference.

A colder pattern will begin to settle in over the next week. But snowfall prospects for the big cities of the East will remain low. Interior sections, especially the lake effect belt, central/upstate New York into central and northern New England could see a moderate or significant snowfall.

Tomorrow will see temperature begin to turn milder with the temperature reaching 50° or somewhat higher. Monday and Tuesday will be the warmest days. Temperatures will top out in the middle and perhaps upper 50s. Afterward colder air will begin to move into the region. On account of successive waves of cold, the first two weeks of December will likely feature mainly below normal temperatures. The long-range guidance is in good agreement for a cold first half of December. 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 +0.2°C and the Region 3.4 anomaly was 0.0°C for the week centered around November 13. For the past six weeks, the ENSO Region 1+2 anomaly has averaged -0.20°C and the ENSO Region 3.4 anomaly has averaged -0.30°C. Neutral ENSO conditions may evolve into a La Niña event during the late fall. Uncertainty as to whether a La Niña will develop has increased. The SOI was +19.02 today. The preliminary Arctic Oscillation (AO) was -0.658 today. Based on sensitivity analysis applied to the latest guidance, there is an implied 99% probability that New York City will have a warmer than normal November (1991-2020 normal). November will likely finish with a mean temperature near 51.0° (3.0° above normal).

Overnight, colder air rushed into the region. Rain changed to wet snow for a time even in nearby suburbs where there was a slushy coating of snow in many places. White Plains picked up 2" of snow. The highest amount in the region was 20.0" at High Point, NJ, but that figure was from 8:30 am. The departing storm will likely be followed by a short period of below normal but not exceptionally cold temperatures before it turns milder early next week. A stronger shot of cold could arrive late in the month. The first week of December will likely feature generally below normal temperatures. 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 +0.2°C and the Region 3.4 anomaly was 0.0°C for the week centered around November 13. For the past six weeks, the ENSO Region 1+2 anomaly has averaged -0.20°C and the ENSO Region 3.4 anomaly has averaged -0.30°C. Neutral ENSO conditions may evolve into a La Niña event during the late fall. Uncertainty as to whether a La Niña will develop has increased. The SOI was +12.40 today. The preliminary Arctic Oscillation (AO) was -0.976 today. Based on sensitivity analysis applied to the latest guidance, there is an implied 97% probability that New York City will have a warmer than normal November (1991-2020 normal). November will likely finish with a mean temperature near 51.2° (3.2° above normal).

From Milford, PA from my sister:

Three photos from this morning. White Plains: West Harrison: