bluewave

Ridiculously strong 6SD+ southerly jet streak with the record warmth pushing into Canada.

The best SSW outcomes for us were when the Pacific has cooperated. You can run down the list and see which years worked for us. As has been the case in recent years, it will probably come down to how the Pacific responds. Full list of events https://csl.noaa.gov/groups/csl8/sswcompendium/majorevents.html

POU sets a new December 25th record high of 65°. This makes it the greatest 140 hr temperature rise there for December. The low between hours on the 19th was -3°missing the record low by 1°. So this would make a 68° temperature rise. The chart below only does hourly readings. https://mesonet.agron.iastate.edu/plotting/auto/?_wait=no&q=169&network=NY_ASOS&zstation=POU&hours=140&month=dec&dir=warm&dpi=100&_fmt=png RECORD EVENT REPORT NATIONAL WEATHER SERVICE ALBANY NY 835 AM EST FRI DEC 25 2020 ...RECORD HIGH TEMPERATURE SET AT POUGHKEEPSIE NY... A RECORD HIGH TEMPERATURE OF 65 WAS SET AT POUGHKEEPSIE NY TODAY AT 400 AM. THIS BREAKS THE OLD RECORD OF 63 SET IN 1964. CLIMATE REPORT NATIONAL WEATHER SERVICE ALBANY NY 435 PM EST SAT DEC 19 2020 ................................... ...THE POUGHKEEPSIE NY CLIMATE SUMMARY FOR DECEMBER 19 2020... VALID TODAY AS OF 0400 PM LOCAL TIME. CLIMATE NORMAL PERIOD: 1981 TO 2010 CLIMATE RECORD PERIOD: 1931 TO 2020 WEATHER ITEM OBSERVED TIME RECORD YEAR NORMAL DEPARTURE LAST VALUE (LST) VALUE VALUE FROM YEAR NORMAL ................................................................... TEMPERATURE (F) TODAY MAXIMUM 26 3:08 PM 60 1931 39 -13 25 MINIMUM -3 7:39 AM -4 1989 21 -24 14 AVERAGE 12 30 -18 20

Yeah, the Pacific Jet will continue to dominate into late December. It will be interesting to see if the SSW verifies. If it does, then we’ll have to wait and see if it benefits Eurasia or North America.

First December for NYC with 10”+ of snow and a 60°Christmas. It was also the first 7 year period with 3 years reaching 60° or warmer on Christmas. Data for December 25 - NY CITY CENTRAL PARK, NY Click column heading to sort ascending, click again to sort descending. Date Max Temperature Min Temperature Precipitation Dec Snowfall 2015-12-25 66 57 0.01 T 1982-12-25 64 41 0.02 3.0 1889-12-25 64 43 0.00 6.0 2014-12-25 62 44 0.09 1.0 1940-12-25 62 38 0.00 3.0 1979-12-25 61 50 0.87 3.5 2020-12-25 61 10.5 1964-12-25 60 49 T 3.1

Yeah, the Wantagh mesonet gusted to 53 mph on the South Shore at 58°. Further north in Westchester the Somers station gusted to 71mph while at 61°.

The strongest gusts in the 63 to 78 mph range were in the areas that got to 60° or above. https://mesonet.agron.iastate.edu/wx/afos/p.php?pil=PNSOKX&e=202012251003 Greenwich 71 MPH 1131 PM 12/24 CWOP Stamford 70 MPH 0328 AM 12/25 CWOP Teterboro Airport 67 MPH 0151 AM 12/25 ASOS NYC/La Guardia 63 MPH 0251 AM 12/25 ASOS Jackson Heights 67 MPH 0152 AM 12/25 CWOP Eatons Neck 76 MPH 1248 AM 12/25 WXFLOW Brookhaven 64 MPH 0445 AM 12/25 CWOP Somers 71 MPH 0330 AM 12/25 NYSM Robbins Reef, NJ 78 MPH 0242 AM 12/25 NOS-PORTS

The Queens College sensor at 179 ft gusting to 46 mph. LaGuardia Arpt CLOUDY 58 49 72 S17G29 29.98F Queens College N/A 57 52 82 S22G46 N/A

It helped having the 4 coldest days of the month follow the snowstorm.

The oddity this month for NYC is how mild it has been for a December with a 10”+ snowstorm. Most other Decembers were much colder. But warm and snowy has been a new theme that has emerged since the mid 2000’s. 2020...39.3...so far 2010...32.8 2009...35.9 2003...37.6 2000...31.1 1960...30.9 1948...38.3 1947...34.0 1933....32.7 1916....34.0 1912....39.3 1872....26.7

Yeah, that is a lot of water ready to be released from the snowpack. It should be noted, that while snow depth has markedly decreased across the area since the big winter storm last week; it has really only settled and compressed. Most of the water content is still there; for example at NWS Binghamton the depth is now only 19 inches - now under half what it was - yet it contains slightly more than 3 inches of water. There is a lot of water ready to be released from the dense snowpack, especially for the Susquehanna Basin and Upper Delaware Basin.

The BGM AFD really highlights how extreme an event this is. 645 AM Update... Just adding an extra word to stress, that this is no ordinary Flood Watch; flooding is not just possible but indeed expected, and it will likely be quite significant for much of the area - both the initial flash flood/small stream phase late today into tonight, and the main stem river phase late tonight through Friday. Some of the signals that we look for in the models for flood potential, such as mean integrated water vapor transport, precipitable water, and southerly component of 850 mb winds; are either off-the-charts or nearly so for this time of year. This is a rare set up. This would be a problem even in the absence of snow cover, but unfortunately was also have plenty of water that will be released from deep snowpack in the warm moist and windy conditions later today through tonight - especially the Susquehanna and Upper Delaware basins. Anyone living in a flood- prone area should have a plan and know what to do in the event high water threatens.

The south based blocking has been a theme this month. Notice the warmer than normal temperatures pushing down into the Northeast. This may be related to the record SSTs over the NW Atlantic and cold pool south of Iceland.

We only needed one storm this month for many areas to get to above normal snowfall. That was when the +PNA combined with the -AO-NAO. It really came down to that supercharged 50/50 low we got. Otherwise, the tucked in storm on the 16-17th would have been a warmer event. As it was my area only got 4” of snow due to the WAA aloft and quick flip to sleet. The month will end milder than models were expecting just several days ago. You mentioned the trade wind surge a few days ago. That may be related to why we are getting the Niña ridge showing up north of Hawaii. But this is still occurring with other more Niño-like features. We would definitely need more help from the PNA in January to counter the +EPO and fast Pacific Jet. But those short term details usually don’t show up on the longer range forecasts. Just a little +PNA can go a long way with -AO -NAO. Slight Niña Ridge poking up north of Hawaii allowing more of a trough out West

That’s why we have to wait for the individual short waves. We will definitely need help from the PNA with such a strong PAC Jet and +EPO. But models won’t show those fine details until we get within about a week of the actual forecast period.

Clash of the Titans pattern on the EPS 11-15 day mean. Firehose Pacific Jet vs one of the strongest -NAO -AO blocks that we have seen in early January. We need to get a nice retrogression of the Greenland block back toward the PNA region. A small +PNA rise can go a long way with a North Atlantic look like that. So some interesting tracking coming up in January when the individual short waves come into better focus.

This would be a new record for this time of year.

That’s the challenge with the raw 2m temperatures. They are often too low with surface temperatures during very strong WAA events. The NAM MOS is 61 at EWR instead of 55 raw. KEWR NAM MOS GUIDANCE 12/23/2020 1200 UTC DT /DEC 23/DEC 24 /DEC 25 /DEC 26 HR 18 21 00 03 06 09 12 15 18 21 00 03 06 09 12 15 18 21 00 06 12 N/X 41 59 53 53 27 TMP 44 46 44 42 42 43 45 50 53 54 55 59 61 61 59 53 51 47 42 32 28 Raw TSRA 008OVC389 0.0 2.3 45 12/25 09Z 55 54 159 29 0.27 0.01 559 558 11.0 -13.1 998 100 -TSRA 006OVC387 0.0 8.3 48 12/25 12Z 55 54 196 12 0.75 0.06 557 556 7.4 -12.9 999 100

South Florida and New England will have similar temperatures for a time Christmas morning.

We just need the trough out West to shift east under the block after New Years. But you can see how the models are showing more ridge in the East now than 3 days ago to close out the year. The wave break and record block south of Greenland is too south based next week with no room for cold 50/50 low pattern. New run Old run

Flood watch issued to our north. && .HYDROLOGY... Flood Watch in effect for much of the region (except Herkimer, Hamilton, Fulton and northern Warren counties) from 6 PM Thursday to 6 PM Friday... A storm system and cold front approaching from the west will bring the threat for moderate to heavy rain to the region late Thursday into early Friday morning. In addition, there is the possibility for a several hour period of strong winds and above freezing temperatures, which may allow for significant snowmelt. Rainfall amounts of 1-3 inches are expected Thursday afternoon and night, with greatest amounts expected across the SE Catskills. The extent of snowmelt will depend on how slow the front moves through the region, with slower movement allowing for a greater length of time for warm temperatures and strong winds to ripen and potentially melt out the snowpack. This potential for melting currently appears greatest across western New England, extending into the mid Hudson Valley and SE Catskills, however could occur farther north if the front moves slower. Due to this potential for heavy rain, and possible significant snow melt, a flood watch has been issued for much of the region from Thursday evening through Friday afternoon. Trends will be watched closely, especially regarding snowmelt potential, over the next few days to determine potential extent of flooding. Minor to possibly moderate river flooding will be possible along with urban and small stream flooding, especially where storm drains remain clogged from snow and ice.

The block starts out too far south next week on the latest EPS. So the EPS doesn’t leave room for a cold 50/50 low pattern. It looks like milder temperatures this run in the 6-10 day period.

Not sure how much snowpack will be left even at the ski resorts by Christmas morning. The Euro has 50° Dewpoints and 2.00”+ heavy rains around the Catskills and Poconos.

Widespread 60-70 mph gusts on the 12z NAM and GFS.

The warming state of the planet has been the ultimate competing influence.