bluewave

Yeah, this was our first La Niña with a NYC 6”+ snowstorm in the week before Christmas since 1995. While patterns have changed greatly since then, maybe we could get another shot a major snow event like we did in early January 1996. It may come down to how strong the wave break is with the Christmas storm. The one on December 1st resulted in the record block east of Newfoundland. That blocking eventually shifted poleward and we got our significant snow event this week. Models are going for another big block east of Newfoundland after the Christmas storm. Beyond that time, models may not yet have a handle on how the blocking east of the Maritimes progresses. We can remember how models greatly underestimated the blocking over the North Pole this past week from the day 10-15 period. It suddenly popped up in the 7-9 day forecasts. So we need to watch for something like that near the end of December. That could potentially set the table for another significant snow event. The animation below is an excellent example of how blocking since early December shifted poleward over time. https://www.cpc.ncep.noaa.gov/products/intraseasonal/z500_nh_anim.shtml

I was posting cold model runs last week for this week when the models latched onto the big block over the North Pole. But the coastal sections had to deal with WAA around 850mb which I pointed out that lead to the sleet and the cement snowpack. You have to take the weather as it comes. What good would it be to only show the weather you like and ignore the kinds that you don’t. All different types of weather have an impact. There are many posters on this forum that are interested in a wide variety of weather. Imagine turning on you local weather forecast and they only showed a preferred type of weather and ignored all the rest.

Flood potential on the 12z Euro around Christmas. Especially for the interior areas with a 20-40” snowpack. Euro has heavy elevated convection and temperatures into the 50s in those areas. Maybe we can slowly melt our pack each day so there isn’t a more rapid melt like they could get north and west of the area if this solution verified.

If the guidance is anywhere close, this could be the 10th solstice warm up in a row with 55°+ temperatures. Time Series Summary for NY CITY CENTRAL PARK, NY Click column heading to sort ascending, click again to sort descending. Ending Date Highest Max Temperature Dec 18 to Dec 25 Missing Count 2019-12-25 57 0 2018-12-25 61 0 2017-12-25 55 0 2016-12-25 58 0 2015-12-25 72 0 2014-12-25 62 0 2013-12-25 71 0 2012-12-25 56 0 2011-12-25 62 0

The storm around Christmas may turn into another wave breaker event like near the start of December. Notice the extreme block the models are moving to following the storm east of Newfoundland. That is very similar to what happened back in early December. This early December block east of the Maritimes came before the blocking built into the Arctic like we just saw. So maybe the Christmas storm will set the table for another -AO drop into January followed by the next major snowstorm potential.

Record warmth to some type of snowfall record is becoming more frequent in recent years. November 2020 was the warmest on record in NYC at 53.0°...5th earliest seasonal 10.0”+ snowfall of 10.5” in December January to March 2020 was the 2nd warmest on record in NYC at 42.4°...trace of snow on May 9th tied with 1977 for latest on record after 7th coldest winter at 28.3° February 2018 was the warmest on record around the area with a first 80° at Newark .....NYC warmest February at 42.0°....ISP snowiest March at 31.9” of snow December 2015 was warmest on record with a +13.3...50.3° in December....greatest snowstorm on record in NYC during January of 27.5” January 2006 was the 4th warmest in NYC at 40.9° followed by the 2nd biggest snowstorm in February of 26.9”

The previous record wasn’t even 4 years old yet. The warming background state, increased moisture, and strong blocking pattern seem to be the underlying causes. Notice how warm the months before these two record storms were. Local warmth Time Series Summary for Binghamton Area, NY (ThreadEx) - Month of Nov Click column heading to sort ascending, click again to sort descending. Rank Year Mean Avg Temperature Missing Count 1 1975 44.6 0 2 2011 44.4 0 3 2001 44.3 0 4 2015 44.1 0 5 2006 43.0 0 6 1964 42.9 0 7 2020 42.8 0 - 2009 42.8 0 Time Series Summary for Binghamton Area, NY (ThreadEx) - Month of Feb Click column heading to sort ascending, click again to sort descending. Rank Year Mean Avg Temperature Missing Count 1 1984 33.1 0 2 2017 31.5 0 CONUS warmth November 2020 The average November temperature across the contiguous U.S. was 46.4 degrees F (4.7 degrees above average), which placed the month at the fourth-hottest Novemberin the 126-year record. The February 2017 temperature was 41.2°F, 7.3°F above the 20th century average. This ranked as the second warmest February in the 123-year period of record. Only February 1954 was warmer for the nation at 41.4°F. Most locations across the contiguous U.S.were warmer than average during February.Feb 28, 2017 RECORD EVENT REPORT...UPDATED NATIONAL WEATHER SERVICE BINGHAMTON, NY 1215 PM EST THU DEC 17 2020 ...SNOWFALL RECORDS SET AT BINGHAMTON NY... THE 2 DAY SNOWFALL AS OF 1015 AM IS 39.9" AT THE GREATER BINGHAMTON AIRPORT IN THE TOWN OF MAINE, NY. THIS BREAKS THE ALL TIME RECORD FOR 2 DAY SNOWFALL. THE OLD RECORD WAS 35.3" SET MARCH 14 TO 15, 2017. THE ONE DAY SNOWFALL FROM TODAY IS 26.3" AS OF 1015 AM. THIS IS THE SECOND GREATEST SNOWFALL FOR ANY CALENDAR DAY. THE GREATEST ONE DAY SNOWFALL IS 31.2" ON MARCH 14TH, 2017. ...SNOW DEPTH RECORD SET AT BINGHAMTON NY... THE SNOW DEPTH THIS MORNING AT 7 AM WAS 39 INCHES. THE OLD RECORD WAS 35 INCHES ON MARCH 15 1993 AFTER A BLIZZARD. RECORDS HERE AT THE GREATER BINGHAMTON AIRPORT GO BACK TO 1951.

The big blocking high that quickly developed over the Arctic in the 6-10 day forecast period closed the deal. But the EPS did a good job forecasting the overall pattern. One of the better EPS performances from late November into December.

Updated for Dec 16-17,2020 https://nwschat.weather.gov/p.php?pid=202012171928-KOKX-NOUS41-PNSOKX 1 S EAST TREMONT 12.4 IN 0145 PM 12/17 TRAINED SPOTTER

The model they are developing to replace the NAM missed the change to sleet that the NAM had around 8pm. So it will need more work in the future to be able to capture strong WAA around the 850mb level. https://www.emc.ncep.noaa.gov/mmb/bblake/fv3/

While we have surpassed many previous snowfall records since 1994, that winter really stands as the last widespread severe ice storm. I had an ice storm in Long Beach on Valentine’s Day 2007 and Feb 2, 2011. But neither one of those were on par with Jan 1994. Jan 94 was my only ice storm in Long Beach lasting over 12 hours. It was remarkable how even Long Beach was able to stay in the 20s with freezing rain from the early morning into the night.

This looks like the 5th earliest 10” snowstorm for NYC. #1 Nov 26-27, 1898....10.0”. #2 Dec 5-7.......2003....14.0” #3 Dec11-12...1960.....15.2” #4 Dec 15th.....1916.....12.7” #5 Dec 16-17....2020.....10.0”

https://vlab.ncep.noaa.gov/web/environmental-modeling-center/fv3-convective-allowing-forecast-system UNIFIED FORECAST SYSTEM : CONVECTIVE-ALLOWING FORECAST AND DATA ASSIMILATION SYSTEM UNIFIED FORECAST SYSTEM : Convective-Allowing Forecast and Data Assimilation System 1. Preamble The UFS Convective-Allowing Model (CAM) Working Group’s charge is to create, using the FV3 dynamical core, a convective-allowing ensemble-based data assimilation and forecast system for the 0-3 day range to replace This development is a collaborative effort between NWS (NCEP/EMC), OAR (NSSL, GSD, GFDL), NCAR, the DTC, and academia. Experience gained from the development of earlier operational and experimental CAM systems such as the GSD’s HRRR/HRRRE, the NAM nests from EMC, the NSSL Experimental Warn-on-Forecast System for ensembles (NEWS-e), the NCAR experimental CAM ensemble, and GFDL’s FV3-based CAM efforts, will guide this project as it evolves. The anticipated operational system, the Rapid Refresh Forecast System (RRFS), will be a single-core (FV3) CAM ensemble-based data assimilation and forecast system. The RRFS is planned for operational implementation in FY2023. 2. Background and Development Timeline As part of its commitment to the implementation of a unified forecast system in NCEP’s Production Suite, NOAA is planning to replace NCEP’s myriad mesoscale and convective-allowing systems with new guidance systems based on the FV3 dynamic core. As of July 2018, the NCEP meso/CAM scale modeling suite currently consists of the following components: North American Mesoscale (NAM) system: Runs the Non-hydrostatic Multiscale Model on B-Grid (NMMB). The NAM consists of a North American 12-km parent domain run to 3.5 days and 4 non-moving nests run to 2.5 days at 3-km resolution over the CONUS, Alaska, Puerto Rico, and Hawaii. An additional 1.5 km nest is run over a pre-selected part of the CONUS or Alaska to 1.5 days for fire weather support operations. The NAM features an 6-h data assimilation cycle with hourly analysis updates for the 12 km parent domain and the 3 km CONUS/AK nests. High-Resolution Window (HiResW): Consists of ~ 3-km runs of the NMMB model and two configurations of the ARW model over the CONUS, Alaska, Hawaii, Puerto Rico, and Guam (single ARW run only). High-Resolution Ensemble Forecast (HREF) system: Current/time-lagged HiResW and NAM CONUS nests are used to generate ensemble products. Currentversion is an 8-member ensemble for CONUS with HiresW and NAM CONUS nest members; HREF for Alaska, Hawaii, and Puerto Rico are a 6-member ensemble with HiResW members only. Short-range Ensemble Forecast (SREF) system: Runs at 16 km over North America and currently consists of 26 members (13 NMMB, 13 ARW) with physics/initial condition diversity. The replacement of the SREF and deterministic NAM systems will be based on whether they can be replaced by improved forecast guidance from the FV3-GFS and FV3-GEFS. Rapid Refresh (RAP) and High-Resolution Rapid Refresh (HRRR): The RAP and HRRR are run hourly out to 21 hr and 18 hr, respectively. RAP is run at 13-km resolution over North America (identical to the NAM parent domain), while HRRR is run at 3 km over CONUS. As of July 2018, the 00/06/12/18z HRRR cycles were extended to 36-hr, and the 03/09/15/21z RAP cycles were extended to 39-hr. A HRRR-Alaska system was also added, running every 3 h. NAM development was frozen after the March 2017 upgrade, and RAP/HRRR development with the WRF-ARW model will cease after the RAPv5/HRRRv4 upgrade in 2020. However, operational execution of these modeling and associated DA systems will continue until comparable FV3-based systems are able to give similar performance. The transition of these deterministic modeling systems to FV3-based configurations will be prioritized as follows; these milestones are also summarized in the chart below: FY2019-FV2020 : HRRR v4 implementation and SAR-FV3 development Development of the FV3-based stand-alone regional model (SAR-FV3) to bring its capabilities and performance up toward the current CAM systems Finalize and implement RAPv5/HRRRv4 Add the extended HRRR forecasts to HREF, possibly replace NMMB members in HREF with SAR-FV3 members Preliminary ensemble DA testing with SAR-FV3 Begin evaluation in NOAA testbeds FY2020-FY2021 :SAR-FV3 development/testing for Meso/CAM Finalize porting of HRRR physics into CCPP for use in SAR-FV3 Finalize FV3-based RAP Continue evaluation of FV3 SAR against existing systems Continue development of DA capabilities with SAR-FV3 Continue evaluation in NOAA testbeds FY2021-FY2023 : Evolution to a FV3-based single core Rapidly Refreshed Forecast System (RRFS) : FV3 CAM ensemble with DA Ensemble analysis and forecast system development with SAR-FV3 and JEDI Development of stochastic physics for single core Continue evaluation in NOAA testbeds Pursuant to favorable evaluation, implement v1.0 RRFS [2023] 3. Ongoing Efforts EMC : Developed a limited area regional version of the FV3 and adapted the NCEP Unified Post-Processor (UPP) and Grid-scale Interpolation (GSI) analysis for the FV3SAR. Currently running two real-time forecast experiments: A control run of a 60-h forecast over the CONUS of a 3 km limited area standalone FV3 with initial and boundary conditions from the operational FV3GFS A parallel run of the 3 km FV3 for dynamics/physics tuning tests EMC is also developing a hourly ensemble data assimilation capability with the limited area FV3. GSD : Developing RAP-sized FV3 domain and modifying pre-processing to use RAP instead of GFS / Fv3GFS input for lateral boundary conditions. Working with EMC on developing better grid-spacing uniformity for the continental FV3-RAP domain EMC/GSD/NSSL/Developmental Test Bed Center (DTC) : Develop commonly-shared FV3SAR workflow 4. Links to Relevant Documents/Web Sites Link to CAM Working Group Google Docs folder UFS Implementation Plan UFS Web Portal

Once the models saw the SSW in February, they began to move toward the cold and snowy March.

That’s been my whole point since October. There have been too many competing influences since at least October to use ENSO as a sole indicator. Think of it more like a collection of overlapping influences adding their various inputs to what becomes the actual pattern. Front-loaded doesn’t mean that there can’t or won’t be other periods of active winter weather. On the whole though, La Ninas have been known for early wintery periods. The best winter DJF snowstorm of the 95-96 La Niña was on January 6th and the 00-01 La Niña December 30. The greatest winter snowstorm of the 17-18 La Niña was January 4th. But that doesn’t preclude a March 2018 or even 2001. The super El Niño in 15-16 had the historic event later in January. The 82-83 super El Niño had the best snowstorm of the season in February. Same for the snowiest month during the 09-10 El Niño in February which had a strong backloaded period late winter. So while there has been many overlapping influences, at least we got some element resembling a La Niña this month.

Good to see the new parallel GFS v16 seems to have fixed the cold and suppressed bias if the current v15. I hope whatever model replaces the NAM is able to correctly see strong WAA aloft like the current model does. While the HRRR is good with thunderstorms and squall lines, it’s profiles are way too cold for winter storm events like this one. Current version too cold and suppressed New parallel warmer and further north with the precipitation shield

The last few months have been an extreme example of mixed influences. But at least we can say some element of La Niña has shown up. The La Niña front-loaded early winter snowfall period has worked out. Numerous La Ninas in NYC had a 6”+ storm and or monthly snowfall total for December.

3.5” here in SW Suffolk with rimed flakes and sleet at 29.5°.

Yeah, getting some sleet mixing in here now In SW Suffolk at 8:10.

Very close to the GSB at 29.5°.

Heavy snow continuing in SW Suffolk with estimated 1/4 mile visibility.

Looks like the mixing line is near I-78 now.

I got down to around 1/4 mile in that heavy snow band with giant 1 inch flakes.

Heavy Snow sounding crunchy here in SW Suffolk with giant flakes of 1 inch diameter. So some warmer air may be beginning to work in aloft with such large aggregates.