bluewave

Break out the snow shovels if a pattern like this starts showing up day 8-10. The composite below is the last 10 December 4”+ snowfalls in NYC since 2002. The two most important features are a -AO and Rockies Ridge. I am judging the +PNA by a ridge axis near the Rockies. The raw PNA numbers aren’t as important. But they are usually neutral -0.5 to +0.5 and higher with a ridge in the Rockies. A trough just off the West Coast or near Vancouver can be fine. We just don’t want a big digging trough over the Rockies. Last 10…4”+ December snows in NYC since 2002

The -PNA is more of a December issue. So we won’t get much snow this month if the Pacific pattern change keeps getting pushed back. But it’s less of an issue in JFM. So root for one of those day 11-15 forecast to finally verify.

It’s been tough to get colder patterns later in December since that period is warming more quickly than the early part of the month since 1981. The late December Arctic cold of 2017 was one of the greatest temperature outliers of recent times. This is also why we have seen so much warmth around the solstice to Christmas in recent years.

The reason we are seeing the models push things back is that the useful skill days 11-15 is often too low to detect a pattern change. A useful skill score is defined as 0.6 or greater. So the best that the EPS can do in most cases is about 10.5 days. The GEFS and GEPS are about a day behind at 9.5. So even the highest scoring EPS day 11-15 is still too low skill to detect a pattern change from 1-5 and 6-10 with certainty. So this is why a pattern change showing up day 11-15 needs to make it to 6-10 to be believable. It’s also why we start to see big jumps sometimes right around day 8-10. It’s just the way these models are constructed. But that isn’t to say that a pattern change on the Pacific side can’t eventually happen. Just that you want to see it survive to day 8-10 in order to lock in the specific date. https://www.emc.ncep.noaa.gov/users/verification/headlines/ Description: An Anomaly Correlation Coefficient (ACC) score of 1.0 indicates that the forecast was highly accurate (i.e., essentially perfect) across the Northern Hemisphere. A model is said to have "useful skill" when the ACC score is greater than or equal to 0.6. This plot shows the average forecast day (i.e., forecast length) when the ACC score falls below 0.6 and the GFS loses useful skill EPS in green and GEFS black and GEPS red

Over the last 10 years the average high for the whole month has been 64. There was a slow but steady rise from the 20s to the 80s. But a big jump in the last 10 years of December record warmth. Monthly Highest Max Temperature for NY CITY CENTRAL PARK, NY Click column heading to sort ascending, click again to sort descending. Year Dec Season Mean 64 64 2021 66 66 2020 62 62 2019 58 58 2018 61 61 2017 61 61 2016 60 60 2015 72 72 2014 65 65 2013 71 71 2012 62 62 2011 62 62 Monthly Highest Max Temperature for NY CITY CENTRAL PARK, NY Click column heading to sort ascending, click again to sort descending. Year Dec Season Mean 61 61 1980 64 64 1981 58 58 1982 72 72 1983 59 59 1984 70 70 1985 55 55 1986 59 59 1987 60 60 1988 60 60 1989 53 53 Monthly Highest Max Temperature for NY CITY CENTRAL PARK, NY Click column heading to sort ascending, click again to sort descending. Year Dec Season Mean 60 60 1959 57 57 1958 55 55 1957 59 59 1956 67 67 1955 53 53 1954 61 61 1953 63 63 1952 59 59 1951 64 64 1950 60 60 Monthly Highest Max Temperature for NY CITY CENTRAL PARK, NY Click column heading to sort ascending, click again to sort descending. Year Dec Season Mean 59 59 1929 56 56 1928 60 60 1927 68 68 1926 49 49 1925 58 58 1924 61 61 1923 64 64 1922 57 57 1921 59 59 1920 58 58

It was the only 30” one of our major stations. Maximum 2-Day Total Snowfall for JFK INTERNATIONAL AIRPORT, NY Click column heading to sort ascending, click again to sort descending. Rank Value Ending Date Missing Days 1 30.5 2016-01-23 0 Maximum 2-Day Total Snowfall for LAGUARDIA AIRPORT, NY Click column heading to sort ascending, click again to sort descending. Rank Value Ending Date Missing Days 1 28.2 2016-01-24 Maximum 2-Day Total Snowfall for NEWARK LIBERTY INTL AP, NJ Click column heading to sort ascending, click again to sort descending. Rank Value Ending Date Missing Days 1 27.8 1996-01-08 0 Maximum 2-Day Total Snowfall for NY CITY CENTRAL PARK, NY Click column heading to sort ascending, click again to sort descending. Rank Value Ending Date Missing Days 1 27.5 2016-01-23 0 Maximum 2-Day Total Snowfall for ISLIP-LI MACARTHUR AP, NY Click column heading to sort ascending, click again to sort descending. Rank Value Ending Date Missing Days 1 27.8 2013-02-09 0 Maximum 2-Day Total Snowfall for Philadelphia Area, PA (ThreadEx) Click column heading to sort ascending, click again to sort descending. Rank Value Ending Date Missing Days 1 30.7 1996-01-08 0 Maximum 2-Day Total Snowfall for Mount Pocono Area, PA (ThreadEx) Click column heading to sort ascending, click again to sort descending. Rank Value Ending Date Missing Days 1 32.5 1978-02-07 0 Maximum 2-Day Total Snowfall for ALLENTOWN LEHIGH VALLEY INTERNATIONAL AIRPORT, PA Click column heading to sort ascending, click again to sort descending. Rank Value Ending Date Missing Days 1 31.9 2016-01-23 0 Maximum 2-Day Total Snowfall for Albany Area, NY (ThreadEx) Click column heading to sort ascending, click again to sort descending. Rank Value Ending Date Missing Days 1 42.2 1888-03-13 0 Maximum 2-Day Total Snowfall for Binghamton Area, NY (ThreadEx) Click column heading to sort ascending, click again to sort descending. Rank Value Ending Date Missing Days 1 40.0 2020-12-17 0 Maximum 2-Day Total Snowfall for Boston Area, MA (ThreadEx) Click column heading to sort ascending, click again to sort descending. Rank Value Ending Date Missing Days 1 27.6 2003-02-18 0 Maximum 2-Day Total Snowfall for Burlington Area, VT (ThreadEx) Click column heading to sort ascending, click again to sort descending. Rank Value Ending Date Missing Days 1 35.3 2010-01-03 0 Maximum 2-Day Total Snowfall for Worcester Area, MA (ThreadEx) Click column heading to sort ascending, click again to sort descending. Rank Value Ending Date Missing Days 1 34.5 2015-01-27 0

We will probably make a run on 60° this week which has become the norm in recent years.

The average first 1” in NYC since the super El Niño has been 12-17. But the spread is very wide between 11-15 and 1-23. First/Last Summary for NY CITY CENTRAL PARK, NY Each section contains date and year of occurrence, value on that date. Click column heading to sort ascending, click again to sort descending. Year Last Value First Value Difference Minimum 01-18 (2020) 11-15 (2018) 226 Mean 03-01 12-17 290 Maximum 04-02 (2018) 01-23 (2016) 332 2021 02-19 (2021) 1.2 01-07 (2022) 5.8 321 2020 01-18 (2020) 2.1 12-16 (2020) 6.5 332 2019 03-04 (2019) 2.0 12-02 (2019) 1.3 272 2018 04-02 (2018) 5.5 11-15 (2018) 6.4 226 2017 03-14 (2017) 7.6 12-09 (2017) 4.6 269 2016 02-15 (2016) 1.4 12-17 (2016) 2.8 305 2015 03-20 (2015) 4.5 01-23 (2016) 27.3 308

The primary low looks to cut around the 12th. The models pushed the more favorable pattern back by a few days. So it often takes time to see PNA improvement in a La Niña pattern. New run Old day 11-15 run

Another GFS upgrade that’s actually a downgrade.

Yeah, getting a favorable Pacific isn’t that important for snowfall in Northern New England like it is for us. Some of their snowiest seasons have been out least snowy. They can do great with teleconnections that don’t work for us. Top 10 snowiest seasons in CAR and NYC snowfall Time Series Summary for Caribou Area, ME (ThreadEx) - Oct through Sep Click column heading to sort ascending, click again to sort descending. Rank Season Total Snowfall NYC Snowfall 1 2007-2008 197.8 11.9 2 1954-1955 181.1 11.5 3 2018-2019 165.4 20.5 4 1981-1982 159.8 24.6 5 1972-1973 153.0 2.8 6 2019-2020 151.9 4.8 7 1968-1969 151.6 30.2 8 2013-2014 150.7 57.4 9 1962-1963 147.5 16.3 10 1976-1977 145.9 24.5

December and February have been the toughest winter months to get a cold departure since the super El Niño. NYC Feb 22….+1.4 Jan 22….-3.2 Dec 21….+4.7 Feb 21….-1.1 Jan 21….+2.2 Dec 20…+1.7 Feb 20…+4.8 Jan 20….+6.5 Dec 19….+0.8 Feb 19….+0.9 Jan 19….-0.1 Dec 18…+2.6 Feb 18…+6.7 Jan 18….-0.9 Dec 17…..-2.5 Feb 17…..+6.3 Jan 17….+5.4 Dec 16….+0.8 Feb 16….+2.4 Jan 16….+1.9 Dec 15….+13.3

We have had only 1 colder than average December since 2011. Time Series Summary for NY CITY CENTRAL PARK, NY - Month of Dec Click column heading to sort ascending, click again to sort descending. Year Mean Avg Temperature Departure 2021 43.8 +4.7 2020 39.2 +1.7 2019 38.3 +0.8 2018 40.1 +2.5 2017 35.0 -2.5 2016 38.3 +0.8 2015 50.8 +13.3 2014 40.5 +3.0 2013 38.5 +1.0 2012 41.5 +4.0 2011 43.3 +5.8 2010 32.8 -4.5

The hope is that the longer we sustain a -AO-NAO, the better a chance that we start to get a coastal storm track instead of a cutter. But we’ll probably have to be patient. The signal of the pattern change is when the 11-15 day colder forecast survives to the 6-10.

We didn’t have the record warm pool off the East Coast in 2010 so the SE Ridge wasn’t an issue back then. Notice how models haven’t been able to see the SE Ridge day 11-15 recently. So the colder pattern keeps getting pushed back. I think there is more going on here than the typical errors handling the Pacific Jet. It’s an potential underestimation of warm water feedback process off the East Coast in the long range. SSTs much warmer than 2010 to our east New 6-10 colder gets pushed back Old 11-15 missed the SE Ridge

This may be the first time we get a 6 sigma Greenland Block with a Southeast Ridge. I believe this is the only one since December 16,2010. That one was the all-time blocking record for the Northern Hemisphere. The big difference in 2010 was that there was no SE Ridge and it was much colder. So it follows the trend of warmer -NAO patterns.

Yeah, quite a bit of Pacific variability days 11-15 among the big 3. But I guess this is to be expected. Getting the Pacific Jet right that far out isn’t a model strength.

You can see why the GEFS and GEPS link the Greenland block up with the SE Ridge on todays runs. Notice how they are showing more of a MJO 5-6 than they were a few days ago. This is why the cutter storm track is showing up early in the month. It’s also another example of how day 11-15 forecasts can be so uncertain especially with the data sparse Pacific. So it takes patience with Pacific improvement when we have a La Niña background state.

Peak gust to 66 mph so far in Westchester. https://nwschat.weather.gov/p.php?pid=202211302208-KOKX-NOUS41-PNSOKX LARCHMONT HARBOR 66 MPH KINGS POINT 55 MPH FIRE ISLAND CG 55 MPH KEW GARDEN HILLS 51 MPH 1 ESE NORWALK 57 MPH

Long Island could see some peak gusts in the 50-60 mph range with the heavier downpours later. There isn’t much of an inversion to prevent the 975mb 50KT LLJ from mixing down. So this should be one of our stronger frontal passages in a while.

You are thinking of 1779-1780 when Philly may have had one day above freezing in January which hasn’t happened since then.

Yes.

They can’t since model skill quickly degrades beyond the 1-5, 6-10, and 11-15 day intervals. The study below is only noting the increase in Greenland blocking. We have seen similar record blocks near Alaska over the same period. Plus other regions have seen record blocking. Also notice the range of increasing highs and lows of the NAO with more amplitude to the index. https://rmets.onlinelibrary.wiley.com/doi/full/10.1002/joc.4673 Greenland Blocking Index 1851–2015: a regional climate change signal We present an extended monthly and seasonal Greenland Blocking Index (GBI) from January 1851 to December 2015, which more than doubles the length of the existing published GBI series. We achieve this by homogenizing the Twentieth Century Reanalysis version 2c-based GBI and splicing it with the NCEP/NCAR Reanalysis-based GBI. More recently, since 1981 there are significant GBI increases in all seasons and annually, with the strongest monthly increases in July and August. A recent clustering of high GBI values is evident in summer, when 7 of the top 11 values in the last 165 years – including the two latest years 2014 and 2015 – occurred since 2007. Also, 2010 is the highest GBI year in the annual, spring, winter and December series but 2011 is the record low GBI value in the spring and April series. Moreover, since 1851 there have been significant increases in GBI variability in May and especially December. December has also shown a significant clustering of extreme high and low GBI values since 2001, mirroring a similar, recently identified phenomenon in the December North Atlantic Oscillation index, suggesting a related driving mechanism. We discuss changes in hemispheric circulation that are associated with high compared with low GBI conditions. Our GBI time series should be useful for climatologists and other scientists interested in aspects and impacts of Arctic variability and change.

Still a top 5 and 10 warmest November with a few days to go. Time Series Summary for WESTCHESTER CO AP, NY - Month of Nov Click column heading to sort ascending, click again to sort descending. Rank Year Mean Avg Temperature Missing Count 1 1994 49.2 2 2 2006 48.8 0 3 2011 48.7 0 4 2022 48.5 4 - 2015 48.5 0 - 2009 48.5 0 5 2001 48.0 0 - 1975 48.0 0 6 2020 47.9 0 7 1963 47.5 0 8 2016 46.6 0 9 2003 46.3 0 - 1964 46.3 0 10 1999 46.2 9 - 1966 46.2 0 Time Series Summary for NY CITY CENTRAL PARK, NY - Month of Nov Click column heading to sort ascending, click again to sort descending. Rank Year Mean Avg Temperature Missing Count 1 2020 53.0 0 2 2015 52.8 0 3 2001 52.7 0 4 1979 52.5 0 5 1948 52.4 0 6 1975 52.3 0 7 2011 51.9 0 - 2006 51.9 0 - 1994 51.9 0 - 1931 51.9 0 8 2022 51.5 3 9 1902 51.4 0 10 2009 51.1 0 Time Series Summary for JFK INTERNATIONAL AIRPORT, NY - Month of Nov Click column heading to sort ascending, click again to sort descending. Rank Year Mean Avg Temperature Missing Count 1 1975 52.7 0 2 2015 52.5 0 3 2009 51.0 0 - 2001 51.0 0 4 2022 50.9 3 - 2020 50.9 0 - 1994 50.9 0 5 2011 50.8 0 - 2006 50.8 0 6 1948 50.7 0 7 2016 50.6 0 8 1982 50.4 0 9 1985 50.1 0 10 1999 50.0 0

Record number of 15”+ snowstorms in recent years at Islip. Maximum 3-Day Total Snowfall for ISLIP-LI MACARTHUR AP, NY Click column heading to sort ascending, click again to sort descending. Rank Value Ending Date Missing Days 1 27.8 2013-02-10 0 - 0 2 25.9 1978-02-08 0 - 0 3 24.9 2015-01-28 0 - 0 4 24.7 2022-01-30 0 - 0 5 23.9 2009-12-21 0 - 0 6 23.7 2016-01-25 0 - 0 0 0 7 20.1 1983-02-13 0 - 0 8 19.9 2006-02-13 0 - 0 9 18.4 2018-03-23 0 - 0 10 18.0 2003-02-18 0 11 17.8 1978-01-21 0 - 0 0 12 17.1 1996-01-09 0 0 - 0 - 0 13 17.0 1969-02-11 0 - 0 14 17.0 1967-03-23 0 - 0 0 - 0 0 15 16.0 2018-01-06 0 - 0 - 0 16 16.0 1982-04-08 0 - 0 - 0 1 0 17 15.2 2011-01-13 0 - 0 18 15.2 2005-01-24 0 0 19 15.0 1969-02-09 0 - 0