bluewave

It may have shaved 5-10° off of what the temperatures would have been on a NW flow instead.

I still remember the old wind chill chart before they revised them to less extreme values. https://www.adirondackdailyenterprise.com/opinion/columns/safety-on-the-roads-by-dave-werner/2016/12/wind-chill-values-revised-in-2001/

The 18z HRRR had ocean effect squalls for all of Long Island tomorrow afternoon but it’s still on its own.

Dropping from 55° to near 10° with 50-60 mph gusts will make it feel colder than if it started out in the low 30s before the cold front. The cool little feature which we almost never see with an Arctic front is a SW to WSW flow. The Euro has sound effect snow squalls in Southern Rhode Island. The mesos closer in will probably have a better handle on this. Wonder if those areas could get a surprise overperforming localized snow event?

The one piece of good news is that we didn’t have a 40” snowstorm like in 2020 before this storm. So while there will be heavy rains and flood potential in New England ski country tomorrow, the rapid runoff and landslide potential won’t be like 2020. But anything left will freeze like cement which isn’t the greatest.

NYC has finished every La Niña season in last 30 years with under 20” of seasonal snowfall following a December with under 3”. It must be due to the snowy La Niña seasons having a nice early frontloaded snowfall period. December snowfall doesn’t matter as much in El Niño’s like 14-15 or neutral years like 12-13. Those have traditionally had better backloaded periods. Monthly Total Snowfall for NY CITY CENTRAL PARK, NY Click column heading to sort ascending, click again to sort descending. Year Oct Nov Dec Jan Feb Mar Apr Season 2021-2022 0.0 T 0.2 15.3 2.0 0.4 0.0 17.9 Monthly Total Snowfall for NY CITY CENTRAL PARK, NY Click column heading to sort ascending, click again to sort descending. Year Oct Nov Dec Jan Feb Mar Apr Season 2020-2021 0.0 0.0 10.5 2.1 26.0 T 0.0 38.6 Monthly Total Snowfall for NY CITY CENTRAL PARK, NY Click column heading to sort ascending, click again to sort descending. Year Oct Nov Dec Jan Feb Mar Apr Season 2017-2018 0.0 T 7.7 11.2 4.9 11.6 5.5 40.9 Monthly Total Snowfall for NY CITY CENTRAL PARK, NY Click column heading to sort ascending, click again to sort descending. Year Oct Nov Dec Jan Feb Mar Apr Season 2016-2017 0.0 T 3.2 7.9 9.4 9.7 0.0 30.2 Monthly Total Snowfall for NY CITY CENTRAL PARK, NY Click column heading to sort ascending, click again to sort descending. Year Oct Nov Dec Jan Feb Mar Apr Season 2011-2012 2.9 0.0 0.0 4.3 0.2 0.0 0.0 7.4 Monthly Total Snowfall for NY CITY CENTRAL PARK, NY Click column heading to sort ascending, click again to sort descending. Year Oct Nov Dec Jan Feb Mar Apr Season 2010-2011 0.0 T 20.1 36.0 4.8 1.0 T 61.9 Monthly Total Snowfall for NY CITY CENTRAL PARK, NY Click column heading to sort ascending, click again to sort descending. Year Oct Nov Dec Jan Feb Mar Apr Season 2008-2009 0.0 T 6.0 9.0 4.3 8.3 T 27.6 Monthly Total Snowfall for NY CITY CENTRAL PARK, NY Click column heading to sort ascending, click again to sort descending. Year Oct Nov Dec Jan Feb Mar Apr Season 2007-2008 0.0 T 2.9 T 9.0 T 0.0 11.9 Monthly Total Snowfall for NY CITY CENTRAL PARK, NY Click column heading to sort ascending, click again to sort descending. Year Oct Nov Dec Jan Feb Mar Apr Season 2005-2006 0.0 T 9.7 2.0 26.9 1.3 0.1 40.0 Monthly Total Snowfall for NY CITY CENTRAL PARK, NY Click column heading to sort ascending, click again to sort descending. Year Oct Nov Dec Jan Feb Mar Apr Season 2000-2001 T 0.0 13.4 8.3 9.5 3.8 0.0 35.0 Monthly Total Snowfall for NY CITY CENTRAL PARK, NY Click column heading to sort ascending, click again to sort descending. Year Oct Nov Dec Jan Feb Mar Apr Season 1999-2000 0.0 0.0 T 9.5 5.2 0.4 1.2 16.3 Monthly Total Snowfall for NY CITY CENTRAL PARK, NY Click column heading to sort ascending, click again to sort descending. Year Oct Nov Dec Jan Feb Mar Apr Season 1998-1999 0.0 0.0 2.0 4.5 1.7 4.5 0.0 12.7 Monthly Total Snowfall for NY CITY CENTRAL PARK, NY Click column heading to sort ascending, click again to sort descending. Year Oct Nov Dec Jan Feb Mar Apr Season 1995-1996 0.0 2.9 11.5 26.1 21.2 13.2 0.7 7

Continuation of the coldest temperatures staying to our west in recent years.

The block extending so far south has resulted in the forecast for record December low pressures north of the Lakes. Pressures around 970mb or lower have usually been associated with storm tracks very close to the coast. So it’s an impressive merger of a -3 to -4 -AO block and the SE Ridge. The colder storm track the Euro was showing last Thursday would have been closer to our old climo for +PNA -AO storm tracks. New December record low pressures possible Old forecast from last Thursday more traditional track New run much stronger SE Ridge over the record warm Gulf Stream

Probably closer to 75 mph near the lakeshores with the developing sting jet.

The December blocking episodes have become more south based since the 1970s. So this allows the block to link up with the Southeast Ridge at times. This will be the case again for the storm on Friday. The one common denominator is the increasing record warm pool to our east. This allows the blocks to extend further south than during eras when the SSTs were much colder. 2022 2012-2020 2000-2010 1976-1995

The 12z Euro goes from the mid 50s Friday morning to the low 10s in NYC at night. Has the strongest wind gusts from 50-60 mph with the cold front during the day on Friday. Highs only in the low 20s for Christmas Eve which hasn’t happened since 1989. Time Series Summary for NY CITY CENTRAL PARK, NY Click column heading to sort ascending, click again to sort descending. Rank Ending Date Lowest Max Temperature Dec 24 to Dec 24 Missing Count 1 1872-12-24 13 0 2 1906-12-24 20 0 3 1989-12-24 22 0 - 1983-12-24 22 0 - 1897-12-24 22 0 - 1896-12-24 22 0 - 1892-12-24 22 0 - 1878-12-24 22 0 - 1876-12-24 22 0 4 1975-12-24 23 0 5 1884-12-24 24 0 - 1870-12-24 24 0

This is a super front with a near record 40°drop in around 12 hrs.

The pattern near the end month looks like it will be something out of a super La Niña playbook as the +SOI really ramps up.

The Manhattan heat island emerged between 1890 and 1910. The outer boroughs from the 1920s to the 1940s. So the temperature rise of the last 60 years has nothing to to with UHI. The minimums are rising just as fast in the rural areas as they are in the urban areas.

This year may set a new record for temperature swings around the holidays.

The Western cluster from the EPS last Thursday did a great job. LONG TERM /FRIDAY THROUGH TUESDAY/... ...Once in a Generation Winter Storm to Slam the Region Heading into and THROUGH the Christmas Weekend... Old Man Winter will unleash the full fury of winter upon our region during this period...as an extremely amplified longwave pattern will spawn one of the most intense storm systems in decades to impact the Mid West and Great Lakes region. This system will likely end up setting low pressure records once it passes north of the border and will have the potential to generate at LEAST storm force winds over the Lower Great lakes. As if the very real threat for damaging winds of 60-70 mph were not enough...there will also be the risk for a prolonged...paralyzing heavy lake effect snow event. The very strong to damaging winds, blowing and drifting snow with localized blizzard conditions preceded by a rapid flash freeze all coming right before the Christmas holiday weekend resulted in a *long duration* winter storm watch being issued for western NY. A Winter Storm Watch has also now been issued for Jefferson and Lewis county from midday Friday through Monday. While heavy lake effect snows have already occurred this winter season...this will be the first event with multiple impacts from such intense winds. Winter storm watches are already in effect for parts of western New York with the high component wrapped into the same product. An extremely amplified longwave pattern during this period will spawn one of the most intense storm systems in decades to impact the Mid West and Great Lakes region. This system will likely end up setting low pressure records once it passes north of the border and will have the potential to generate storm force winds over the Lower Great lakes. Explosive cyclogenesis will take place over the mid western states into southern Ontario on Friday...as an anomalously strong 150kt H25 jet will pass through the base of a very deep longwave trough. This will support rapid deepening of a corresponding sfc low that will track southern Ontario by late Friday. The `bombing` low will deepen from roughly 990mb in the vcnty of Lake Erie/Lower Michigan late Thursday night...to 982mb over southernmost Ontario Friday morning to about 968mb near the Ontario-Quebec border by Friday evening... easily meeting the definition of bombogenesis (24mb/24hrs). Such deepening is relatively rare in the LOWER Great lakes...but more common across the UPPER Great Lakes and certainly with Nor`easters along the coast. Some of the parameters of this intense storm are climatologically `off the charts`...such as MSLP and strength of both the low level and upper level jets. One could certainly describe this storm system as a once in a generation type of event. Subtle differences remain...but there remains general model agreement in the overall large scale scenario...which adds confidence.

Yeah, NYC now has a 10 year average around 40° in December. It only took 30 years for us to get what used to be normal for DC in the 1990s. So we are becoming more like the Midatlantic. Monthly Mean Avg Temperature for Washington Area, DC (ThreadEx) Click column heading to sort ascending, click again to sort descending. Year Dec Season Mean 40.2 40.2 2000 31.8 31.8 1999 42.0 42.0 1998 44.4 44.4 1997 41.0 41.0 1996 43.0 43.0 1995 35.6 35.6 1994 44.2 44.2 1993 38.1 38.1 1992 39.6 39.6 1991 42.3 42.3 Monthly Mean Avg Temperature for NY CITY CENTRAL PARK, NY Click column heading to sort ascending, click again to sort descending. Year Dec Season Mean 40.6 40.6 2021 43.8 43.8 2020 39.2 39.2 2019 38.3 38.3 2018 40.1 40.1 2017 35.0 35.0 2016 38.3 38.3 2015 50.8 50.8 2014 40.5 40.5 2013 38.5 38.5 2012 41.5 41.5

The December temperatures have risen about 5 degrees since 1981.

Models have our greatest December 12 hr temperature drop on Friday. Mid 50s around 8am dropping to mid 10s by 8 pm. So a possible 40° drop. The previous record drop was 35°. https://mesonet.agron.iastate.edu/plotting/auto/?_wait=no&q=169&network=NJ_ASOS&zstation=EWR&hours=12&month=dec&dir=cool&how=exact&_r=t&dpi=100&_fmt=png

NYC will need at least 3.0” in December to have a shot at normal or better seasonal snowfall during a La Niña year. This has been the La Niña pattern going back to the 1990s. So it will be interesting to see how we do with snowfall when the month ends in around 10 days. You would think that we a least have a shot before the blocking relaxes near the end of the month. La Ninas since 1991 Monthly Total Snowfall for NY CITY CENTRAL PARK, NY Click column heading to sort ascending, click again to sort descending. Year Oct Nov Dec Jan Feb Mar Apr Season 2021-2022 0.0 T 0.2 15.3 2.0 0.4 0.0 17.9 Monthly Total Snowfall for NY CITY CENTRAL PARK, NY Click column heading to sort ascending, click again to sort descending. Year Oct Nov Dec Jan Feb Mar Apr Season 2020-2021 0.0 0.0 10.5 2.1 26.0 T 0.0 38.6 Monthly Total Snowfall for NY CITY CENTRAL PARK, NY Click column heading to sort ascending, click again to sort descending. Year Oct Nov Dec Jan Feb Mar Apr Season 2017-2018 0.0 T 7.7 11.2 4.9 11.6 5.5 40.9 Monthly Total Snowfall for NY CITY CENTRAL PARK, NY Click column heading to sort ascending, click again to sort descending. Year Oct Nov Dec Jan Feb Mar Apr Season 2016-2017 0.0 T 3.2 7.9 9.4 9.7 0.0 30.2 Monthly Total Snowfall for NY CITY CENTRAL PARK, NY Click column heading to sort ascending, click again to sort descending. Year Oct Nov Dec Jan Feb Mar Apr Season 2011-2012 2.9 0.0 0.0 4.3 0.2 0.0 0.0 7.4 Monthly Total Snowfall for NY CITY CENTRAL PARK, NY Click column heading to sort ascending, click again to sort descending. Year Oct Nov Dec Jan Feb Mar Apr Season 2010-2011 0.0 T 20.1 36.0 4.8 1.0 T 61.9 Monthly Total Snowfall for NY CITY CENTRAL PARK, NY Click column heading to sort ascending, click again to sort descending. Year Oct Nov Dec Jan Feb Mar Apr Season 2008-2009 0.0 T 6.0 9.0 4.3 8.3 T 27.6 Monthly Total Snowfall for NY CITY CENTRAL PARK, NY Click column heading to sort ascending, click again to sort descending. Year Oct Nov Dec Jan Feb Mar Apr Season 2007-2008 0.0 T 2.9 T 9.0 T 0.0 11.9 Monthly Total Snowfall for NY CITY CENTRAL PARK, NY Click column heading to sort ascending, click again to sort descending. Year Oct Nov Dec Jan Feb Mar Apr Season 2005-2006 0.0 T 9.7 2.0 26.9 1.3 0.1 40.0 Monthly Total Snowfall for NY CITY CENTRAL PARK, NY Click column heading to sort ascending, click again to sort descending. Year Oct Nov Dec Jan Feb Mar Apr Season 2000-2001 T 0.0 13.4 8.3 9.5 3.8 0.0 35.0 Monthly Total Snowfall for NY CITY CENTRAL PARK, NY Click column heading to sort ascending, click again to sort descending. Year Oct Nov Dec Jan Feb Mar Apr Season 1999-2000 0.0 0.0 T 9.5 5.2 0.4 1.2 16.3 Monthly Total Snowfall for NY CITY CENTRAL PARK, NY Click column heading to sort ascending, click again to sort descending. Year Oct Nov Dec Jan Feb Mar Apr Season 1998-1999 0.0 0.0 2.0 4.5 1.7 4.5 0.0 12.7 Monthly Total Snowfall for NY CITY CENTRAL PARK, NY Click column heading to sort ascending, click again to sort descending. Year Oct Nov Dec Jan Feb Mar Apr Season 1995-1996 0.0 2.9 11.5 26.1 21.2 13.2 0.7 75.6

It may be our best chance of putting some snow points on the board before the warm up at the end of the month. These strong -AO patterns in a December usually do better than this one has so far. It would be like leaving the bases loaded if we can’t get a least some snow before the month ends.

I don’t think that the models will have a handle on that system until the big storm on Friday gets out of the way.

Beyond identifying model biases day 6-10 and 11-15, it’s a very low skill game to try and guess what happens beyond that range. So we try to use some analogs to fill in the gaps like how low the AO has been in December. One would hope we see more blocking intervals like the list of analogs below. But the sample sizes may never be great enough to account for all the possibilities. December -3 or lower daily values since 2000 and NYC snowfall 12-11-22….-4.2378……? 12-28-20….-3.197……..10.5” 12-8-12…….-3.902……0.4” 12-18-10……-5.265…..20.1” 12-21-09……-5.2821….12.4” 12-05-05……-3.569….9.7” 12-28-01…….-3.293….T 12-29-00……-4.688….13.4”

The tendency to see the -AO block link up with the SE Ridge and become more south based has been a frequent theme. The EPS run last Thursday that had at least a window for a more wintry event didn’t have the linkage. The PNA isn’t much different as the vortex digging into the PACNW hasn’t changed locations from the forecast last week. So the changes leading to the warmer solution look more Atlantic based than Pacific. If we had a stronger +PNA like in December 2020, this probably would have been another potential KU. Verification for today Forecast from last Thursday

The late December warmer correction is another example of the week 2 products running too cold recently. New 240 Old 360