donsutherland1

Four quick thoughts on the upcoming pattern change: 1. The MJO's push into Phase 7 (amplitude > 2) should trigger a circulation response that favors cooler than normal temperatures during the January 1-10 period overall. 2. The magnitude of the cold and its duration remains uncertain. MJO forecasts aren't very skillful beyond a week. Additional factors influence the hemispheric circulation. There remains a risk that severe cold remains largely confined to northwestern/central Canada and the U.S. Northwest/Northern Plains and, if it comes eastward, remains largely north of the U.S.-Canada border. One likely won't have a firm idea as to whether the colder pattern will last closer to two weeks or closer to four weeks until late this month. 3. The December 21-31 period should be cooler than the December 11-20 period. It very likely won't be severely cold based on consistent teleconnections forecasts into the start of that period. 4. In January, an AO-/PNA+ pattern has accounted for a disproportionate share of significant Mid-Atlantic snowstorms. Teleconnections can't be reliably forecast beyond two weeks.

The data is only for December. Yes, as you noted, big storms have occurred as the NAO was rising. During January, an AO-/PNA+ pattern is most favorable for significant snowfalls. I always welcome any snow. Hopefully, we’ll have one or two before December ends.

One caveat concerning the NAO when the PNA is negative in December. Once the NAO falls to or below -1, snowfalls tend to be smaller (biggest daily snowfall: 2.7”, December 27, 1976). Measurable snow fell on 7.3% of days. Between-0.999 and -0.001, nearly 60% of daily snowfalls were 2” or more. The December 26-27, 2010 blizzard was the biggest such storm with 20.0”. This blizzard produced the only days with 6” or more snowfall for this NAO subset. Measurable snow fell on 8.6% of days. Data was from 1950-2020. There were 137 days in the earlier subset (NAO -1 or below) and 267 days in the latter one. Snowfall was from Central Park.

We had more than 3” of snow in December 2020.

Morning thoughts… Today will be mostly sunny, breezy, and mild. High temperatures will likely reach the lower and middle 50s in most of the region. Likely high temperatures around the region include: New York City (Central Park): 53° Newark: 55° Philadelphia: 57° Normals: New York City: 30-Year: 44.9°; 15-Year: 45.6° Newark: 30-Year: 45.4°; 15-Year: 46.2° Philadelphia: 30-Year: 46.6°; 15-Year: 47.5° The unseasonably mild weather will continue into the start of the weekend.

Temperatures rose into the 50s today across most of the region. Similar warmth is likely tomorrow. Parts of the Midwest could see daily and December-record temperatures. Des Moines has a shot at seeing its first ever 70° December day. Some of that warmth will affect the region late in the week before cooler air again returns. No Arctic blasts appear likely for the foreseeable future. Overall, through December 20th, there will likely be only some relatively short-lived cool shots. Afterward, the AO could go negative, increasing the opportunity for colder outcomes. In the Midwest, Chicago has yet to receive its first measurable snowfall through December 12. Only four prior years saw their first measurable snowfall on December 12 or later: 1. December 20, 2012 2. December 16, 1965 3. December 14, 2001 4. December 12, 1946 The base case is that the closing 10 days of December could turn cooler, though not necessarily cold. Since 1950, there have been 7 cases where the AO averaged +2.000 or above during the first week in December, as has been the case this year. The mean December 21-31 temperature in New York City was 40.2°. The median temperature was 41.5°. The coldest was 35.3° (1951) and the warmest was 44.0° (1979). In short, this historic experience would suggest that there will be no severe Arctic outbreaks in the East this month. It also suggests that New York City will likely have an average temperature of 40° or above this month. Afterward, if the small sample of cases where the MJO moved into Phase 7 at a high amplitude (1.75 or above) during the December 10-20 period, as occurred this month, is representative, the first 10 days of January could see below to perhaps much below normal temperatures. Both the magnitude and duration of the cold is uncertain, but the potential pattern change as support on the latest EPS weekly guidance. Following very wet July-September periods, winter (December-February) precipitation has typically been near or below normal. The most recent exception was winter 2018-19. The ENSO Region 1+2 anomaly was -1.4°C and the Region 3.4 anomaly was -1.1°C for the week centered around December 8. For the past six weeks, the ENSO Region 1+2 anomaly has averaged -1.00°C and the ENSO Region 3.4 anomaly has averaged -0.92°C. La Niña conditions will likely persist into at least late winter. The SOI was +12.92 today. The preliminary Arctic Oscillation (AO) figure was +0.395 today. On December 11 the MJO was in Phase 7 at an amplitude of 2.411 (RMM). The December 10-adjusted amplitude was 2.425 (RMM). Based on sensitivity analysis applied to the latest guidance, there is an implied 87% probability that New York City will have a warmer than normal December (1991-2020 normal). December will likely finish with a mean temperature near 42.4° (3.3° above normal).

I believe we will probably see a cooler period during the first 10 days of January given the atmospheric response to the MJO’s move into Phase 7 at a very high amplitude. I am not sure whether there will be severe cold nor whether such a pattern would persist more than 2 weeks. It’s possible most of the severe cold will remain confined to the west.

Building on yesterday's post concerning the pattern evolution, the prospects of a colder than normal start to January have continued to increase. The MJO has now moved into Phase 7 at a very high amplitude (2.000 or above). The number of cases where the MJO moved into Phase 7 at amplitudes of 2 or above (n=3) or 1.75 or above (n=4) during December 10-20 is small. However, those cases overwhelmingly saw January 1-10 wind up colder or perhaps much colder than normal. January 1-10 Temperatures for New York City and Philadelphia: New York City: Mean: 26.1° Lowest: 21.2°, 2018 Highest: 34.1°, 2002 1991-2020 Mean: 34.8° Philadelphia: Mean: 26.1° Lowest: 20.7°, 2018 Highest: 34.5°, 2002 1991-2020 Mean: 35.2°

Morning thoughts… Today will be mostly sunny, breezy, and mild. High temperatures will likely reach the lower and middle 50s in most of the region. Likely high temperatures around the region include: New York City (Central Park): 53° Newark: 56° Philadelphia: 56° Normals: New York City: 30-Year: 44.9°; 15-Year: 45.6° Newark: 30-Year: 45.4°; 15-Year: 46.2° Philadelphia: 30-Year: 46.6°; 15-Year: 47.5° The unseasonably mild weather will continue into the start of the weekend.

Another warmup is poised to unfold starting tomorrow. Parts of the Midwest could see daily and December-record temperatures. Des Moines has a shot at seeing its first ever 70° December day. Some of that warmth will affect the region late in the week before cooler air again returns. No Arctic blasts appear likely for the foreseeable future. Overall, through December 20th, there will likely be only some relatively short-lived cool shots. Afterward, the AO could go negative, increasing the opportunity for colder outcomes. In the Midwest, Chicago has yet to receive its first measurable snowfall through December 11. Only four prior years saw their first measurable snowfall on December 11 or later: 1. December 20, 2012 2. December 16, 1965 3. December 14, 2001 4. December 12, 1946 The base case is that the closing 10 days of December could turn cooler, though not necessarily cold. Since 1950, there have been 7 cases where the AO averaged +2.000 or above during the first week in December, as has been the case this year. The mean December 21-31 temperature in New York City was 40.2°. The median temperature was 41.5°. The coldest was 35.3° (1951) and the warmest was 44.0° (1979). In short, this historic experience would suggest that there will be no severe Arctic outbreaks in the East this month. It also suggests that New York City will likely have an average temperature of 40° or above this month. Following very wet July-September periods, winter (December-February) precipitation has typically been near or below normal. The most recent exception was winter 2018-19. The ENSO Region 1+2 anomaly was -1.1°C and the Region 3.4 anomaly was -0.9°C for the week centered around December 1. For the past six weeks, the ENSO Region 1+2 anomaly has averaged -0.87°C and the ENSO Region 3.4 anomaly has averaged -0.92°C. La Niña conditions will likely persist into at least late winter. The SOI was +12.40 today. The preliminary Arctic Oscillation (AO) figure was +1.290 today On December 10 the MJO was in Phase 6 at an amplitude of 2.423 (RMM). The December 9-adjusted amplitude was 2.539 (RMM). Based on sensitivity analysis applied to the latest guidance, there is an implied 85% probability that New York City will have a warmer than normal December (1991-2020 normal). December will likely finish with a mean temperature near 42.3° (3.2° above normal).

The long-range guidance is looking somewhat more promising. However, through the 20th, readings remain likely to average above normal with any cold shots being transient and modest. During the closing 10 days of the month, a somewhat cooler but not very cold regime could begin to unfold. If a period of sustained below normal temperatures will develop, one might need to wait for the first week in January. Then, we’ll have to see whether such a pattern could be sustained or would wind up breaking down within two weeks or so. We’ll also have to wait to see if the severe cold from Alaska/NW Canada moves into the region or remains largely confined to Canada as it spreads eastward. For perspective, below are the mean temperatures for NYC for 12/21-25 for the last four runs of the EPS: 12/11 0z: 37.7 12/11 0z: 37.0 12/12 0z: 36.7 12/12 12z: 37.9 That’s not much of a change. It’s also somewhat warmer than normal.

He might be referring to winter 2018-19 and March 2019. 2019-20 was among the least snowy winters on record.

Morning thoughts… Today will be partly sunny, breezy, and noticeably cooler. High temperatures will likely reach the upper 40s and lower 50s in most of the region. Likely high temperatures around the region include: New York City (Central Park): 49° Newark: 52° Philadelphia: 51° Normals: New York City: 30-Year: 45.2°; 15-Year: 45.8° Newark: 30-Year: 45.7°; 15-Year: 46.5° Philadelphia: 30-Year: 46.9°; 15-Year: 47.7° Milder air will begin to return tomorrow.

59. It was well short of its daily record due to a persistent onshore wind.

Although it was mostly cloudy throughout the region, daily record high temperatures were matched or broken in many parts of the region. Those records included some dusty 19th century antique marks. Record temperatures through 7 pm included: Allentown: 63° (old record: 61°, 1952 and 1979) Atlanta: 75° (tied record set in 2007) Baltimore: 70° (old record: 66°, 1971) Buffalo: 67° (old record: 61°, 1899) Harrisburg: 68° (old record: 63°, 1897) New York City-LGA: 67° (old record: 62°, 1971) New York City-NYC: 66° (old record: 64°, 1879) Newark: 68° (old record: 65°, 1966 and 1971) Philadelphia: 68° (old record: 65°, 1899 and 1971) Poughkeepsie: 64° (old record: 63°, 1966) Rochester: 64° (tied record set in 2015) Scranton: 64° (tied record set in 1979) Syracuse: 64° (old record: 62°, 1979) Toronto: 64° (old record: 56°, 1979) Trenton: 65° (tied record set in 1911) Washington, DC: 70° (old record: 68°, 1897, 1971 and 1979) Wilmington, DE: 67° (old record: 66°, 1971) Wilmington, NC: 80° (old record: 79°, 2007) Baltimore's 70° temperature was that city's record 189th such day. The previous record was 187 days, which was set in 2017. A cold front will move across the region this evening and tonight. It could bring some heavy showers and thundershowers, damaging winds, and perhaps some hail. This cold front will bring a transient shot of somewhat cooler air to the region. Another warmup is possible beginning next week. No Arctic blasts appear likely for the foreseeable future. Overall, through December 20th, there will likely be only some relatively short-lived cool shots. Afterward, the AO could go negative, increasing the opportunity for colder outcomes. In the Midwest, Chicago has yet to receive its first measurable snowfall through December 10. Only five prior years saw their first measurable snowfall on December 10 or later: 1. December 20, 2012 2. December 16, 1965 3. December 14, 2001 4. December 12, 1946 5. December 10, 2003 The base case is that the closing 10 days of December could turn cooler, though not necessarily cold. Since 1950, there have been 7 cases where the AO averaged +2.000 or above during the first week in December, as has been the case this year. The mean December 21-31 temperature in New York City was 40.2°. The median temperature was 41.5°. The coldest was 35.3° (1951) and the warmest was 44.0° (1979). In short, this historic experience would suggest that there will be no severe Arctic outbreaks in the East this month. It also suggests that New York City will likely have an average temperature of 40° or above this month. Following very wet July-September periods, winter (December-February) precipitation has typically been near or below normal. The most recent exception was winter 2018-19. The ENSO Region 1+2 anomaly was -1.1°C and the Region 3.4 anomaly was -0.9°C for the week centered around December 1. For the past six weeks, the ENSO Region 1+2 anomaly has averaged -0.87°C and the ENSO Region 3.4 anomaly has averaged -0.92°C. La Niña conditions will likely persist into at least late winter. The SOI was +14.79 today. The preliminary Arctic Oscillation (AO) figure was +1.368 today On December 9 the MJO was in Phase 6 at an amplitude of 2.539 (RMM). The December 8-adjusted amplitude was 2.194 (RMM). Based on sensitivity analysis applied to the latest guidance, there is an implied 88% probability that New York City will have a warmer than normal December (1991-2020 normal). December will likely finish with a mean temperature near 42.4° (3.3° above normal).

Some photos from this morning’s passage of the warm front:

Phone apps, if this is an app, may not necessarily use the Central Park reading.

NWS New York NY @NWSNewYorkNY · 16m Central Park has also broken the high temperature record for 12/11 with a 65° reading. This breaks the old record of 64° that was set in 1879. #NYCwx #NYwx

It really depends where the warm air is pushing. Usually LGA and JFK respond fairly quickly. Elsewhere, Boston rose 14 degrees in the past hour from 47 to 61.

Newark has now reached 66. The old record was 65, which was set in 1966 and tied in 1971.

Morning thoughts… Today will be mostly cloudy and very warm. Temperatures will approach or break daily records. Showers and strong to perhaps severe thunderstorms are likely later in the day or at night. It will also become very windy. High temperatures will likely reach the lower and middle 60s in most of the region. Likely high temperatures around the region include: New York City (Central Park): 62° Newark: 66° Philadelphia: 67° Normals: New York City: 30-Year: 45.5°; 15-Year: 46.1° Newark: 30-Year: 46.0°; 15-Year: 46.8° Philadelphia: 30-Year: 47.1°; 15-Year: 48.0° Tomorrow will be partly sunny, breezy and cooler. Daily records for December 11: Allentown: 61°, 1952 and 1979 Baltimore: 69°, 1979 New York City: 64°, 1879 Newark: 65°, 1966 and 1971 Philadelphia: 65°, 1899 and 1971 Washington, DC: 68°, 1897, 1971, and 1979

1st measurable snow in Denver and record-tying number of days without measurable snow. https://twitter.com/NWSBoulder/status/1469513290044764160?s=20

It’s been a terrible night. A nursing home took a direct hit. Waiting on the news, but there were probably numerous casualties.

Temperatures will likely soar to near record and record levels tomorrow in the Middle Atlantic region in advance of another cold front. The air mass that will send temperatures reaching for records resulted in numerous records including: Greenville, MS: 84° (old record: 82°, 1918) ***2nd highest December temperature*** Little Rock: 78° (tied record set in 1889) Shreveport: 84° (old record: 78°, 2020) ***Tied December Record*** Passage of the front could be marked by strong winds and strong to perhaps severe thunderstorms. The front will bring a transient shot of somewhat cooler air to the region. A significant warmup is possible beginning after the middle of next week. No Arctic blasts appear likely for the foreseeable future. Overall, through December 20th, temperatures will likely be warmer than normal in the means with some short-lived cool shots. Afterward, the AO could go negative, increasing the opportunity for colder outcomes. Out West, Denver finally picked up its first measurable snowfall of the season. The previous record latest first measurable snowfall occurred on November 21, 1934. The progression of Denver's latest first measurable snowfall of the season is as follows: November 11, 1882 November 16, 1894 November 19, 1931 November 21, 1934 December 10, 2021 The base case is that the closing 10 days of December could turn cooler, though not necessarily cold. Since 1950, there have been 7 cases where the AO averaged +2.000 or above during the first week in December, as has been the case this year. The mean December 21-31 temperature in New York City was 40.2°. The median temperature was 41.5°. The coldest was 35.3° (1951) and the warmest was 44.0° (1979). In short, this historic experience would suggest that there will be no severe Arctic outbreaks in the East this month. It also suggests that New York City will likely have an average temperature of 40° or above this month. Following very wet July-September periods, winter (December-February) precipitation has typically been near or below normal. The most recent exception was winter 2018-19. The ENSO Region 1+2 anomaly was -1.1°C and the Region 3.4 anomaly was -0.9°C for the week centered around December 1. For the past six weeks, the ENSO Region 1+2 anomaly has averaged -0.87°C and the ENSO Region 3.4 anomaly has averaged -0.92°C. La Niña conditions will likely persist into at least late winter. The SOI was +9.13 today. The preliminary Arctic Oscillation (AO) figure was +1.143 today On December 8 the MJO was in Phase 6 at an amplitude of 2.189 (RMM). The December 7-adjusted amplitude was 2.014 (RMM). Based on sensitivity analysis applied to the latest guidance, there is an implied 84% probability that New York City will have a warmer than normal December (1991-2020 normal). December will likely finish with a mean temperature near 42.3° (3.2° above normal).

NWS Boulder: Denver: 0.3” snow