bluewave

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.

We started to see these ENSO disconnects when the 15-16 super El Niño California rainfall got delayed into the 16-17 La Niña. Then it was off to the races when the El Niño didn’t couple in 18-19. Last winter we saw weak El Niño conditions produce an 11-12 style La Niña pattern. So it’s no surprise we are getting an El Niño-like pattern with a moderate La Niña.

We have seen these strong trade wind surges and Niño 3.4 dipping temperatures back to the fall. All the competing influences have resulted in a more Niño-like pattern. Notice how the PNA is forecast to stay positive right into January. Beyond early January, it will be interesting to see which type ENSO pattern prevails.

Another El Niño-like feature that we are experiencing this month is the mild average temperature combined with the 10”+ snow in NYC . Since 1995 , all the 35.9° or warmer Decembers with 10”+ were warmer ENSO years. The snowy La Niña Decembers all had a monthly average around 32° degrees. This month is already 39.1° before the big coming solstice warm up. An interesting question to ask is how long can we keep this Niño-like pattern going? I looks like January will at least start out more Niño-like. So it will be interesting to see which ENSO type pattern shows up in February. Warmest Decembers highlighted...NYC snowfall....average temperature....Niño 3.4 temperature.... Time Series Summary for NY CITY CENTRAL PARK, NY - Month of Dec Click column heading to sort ascending, click again to sort descending. Rank Year Total Snowfall Temp/ Niño 3.4 1 2010 20.1 32.8/-1.6 2 2003 19.8 37.6/+0.4 3 2000 13.4 31.1/-0.7 4 2009 12.4 35.9/+1.6 5 1995 11.5 32.4/-1.0 6 2002 11.0 36.0/+1.1 7 2020 10.5 39.1/-1.2

NYC is on track for its first Christmas with a morning high of 55-60 and an evening low in the 20s. Our new era of big temperature swings continues. The previous coldest temperature on Christmas with such a warm high was 33° in 2008. 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 Snowfall Snow Depth 2015-12-25 66 57 0.01 0.0 0 1982-12-25 64 41 0.02 0.0 0 1889-12-25 64 43 0.00 0.0 M 2014-12-25 62 44 0.09 0.0 0 1940-12-25 62 38 0.00 0.0 0 1979-12-25 61 50 0.87 0.0 0 1964-12-25 60 49 T 0.0 0 1994-12-25 59 41 T 0.0 0 1965-12-25 59 47 0.65 0.0 0 1932-12-25 59 47 0.13 0.0 0 1893-12-25 58 45 0.00 0.0 M 2008-12-25 57 33 0.13 0.0 0 1936-12-25 56 40 0.00 0.0 0 1933-12-25 55 34 0.00 0.0 0 1915-12-25 55 38 0.01 0.0 0

It’s been a big year for squall lines. This could be one of the most intense low topped squall lines that we have seen on Christmas. I wonder what the annual record number is for all types of squall lines in the region?

Yeah, this month looks like a continuation of the atmospheric coupling weirdness of recent years. The 500 mb pattern is much more El Niño-like. Especially the deep Aleutian Low and +PNA. I guess that this makes up for the last 2 winters which were technically El Niño with La Niña-like 500 mb patterns.

I am not sure why my original post was quoted so many times. All that I said is that the interior areas with the deepest snowpack would have to watch the shorter term forecasts for flooding potential. I didn’t go into any specifics since it was based on the longer range Euro.This is very similar to the BGM AFD. I also mentioned that the coastal sections would have time to gradually melt their smaller snowpack over the next several days before the storm arrives. 2 inch rainfall totals are not out of the question for those enhanced higher terrain locations. Combined rain and snowmelt could result in significant runoff and thus potential for flooding will need to be monitored closely. Finally, weight of old snow and new rain on rooftops where heaviest recent snow occurred, could lead to problems.

The Euro has one of the strongest south based blocks that we have seen this time of year. It has a whopping +6 SD 500 mb height anomaly just south of Greenland. A 584 dm ridge east of Newfoundland should be very close to the record in late December.

The timing of the Christmas cold front looks to be early Christmas morning. The EURO and new GFS V16 are pretty close. So the high for the day will be early with falling temperatures after. Another big temperature swing weather pattern.

Yeah, having a much warmer than average NW Atlantic nearby makes a big difference. ISP has had 5 events of 17” or greater since the 09-10 winter. MSP recorded one 17” snowstorm over the same period. for ISLIP-LI MACARTHUR AP, NY 27.8 2013-02-09 24.9 2015-01-27 23.9 2009-12-20 23.7 2016-01-24 18.4 2018-03-22 for Minneapolis-St Paul Area, MN (ThreadEx) 17.3 2010-12-11

The Christmas storm wave break looks like it may be off the charts. The ridge just south of Greenland goes more than +5 SD. This could be one the strongest blocks in that region for this time of year. So we will be probably be looking at winter storm threats from the end of December right into January.

Walt, great thread as usual. As I posted in the other thread, the new parallel GFS v16 did much better than the current OP v15 with the major winter storm this week. It didn’t have the cold and suppressed bias that has been a problem in the current OP. So it’s not a surprise that the v16 is warmer and slower than the current OP for the major storm around Christmas. New parallel v16 GFS Current V15 OP

Moving into our annual solstice warm up this week. Followed by a return to cooler than normal after Christmas. The Southeast will turn out to be the coldest part of the CONUS relative to the means this month. Florida is on track for their first colder than average month since March 2018.

I guess that he only ran the model for that storm. But it’s also happening in places like Japan. https://www.washingtonpost.com/weather/2020/12/18/japan-snow-stranded-motorists/

The WAA aloft and dryslot did their thing.