The "Wow" Snow Storm - Another Historic Blockbuster
Wednesday Night-Thursday Morning: December 16-17, 2020

NOAA Visible Satellite Image
Early Thursday morning December 17, 2020
Nor 'easter with apparent eye feature southeast of Long Island

Visible Satellite Picture of the storm, early Thursday morning December 17, 2020 

Storm Breakdown for Albany
These exact records were set in the December 1-3, 2019 storm, eclipsed here by 0.3". In the 2019 storm, however, the 22.6" of snow took 39 hours to accumulate. In this storm, the 22.9" that accumulated took approximately 12 hours, with the majority of the snow in fact falling in only 6-7 hours. Snowfall rates of 2"-3" per hour were common between 2 and 8am with astounding snowfall rates of 5"-6" calculated in a "Mega" snow band that set up just north of Albany producing snow accumulations in a fairly narrow axis of 24"-35" with locally up to 44" in parts of Washington and Bennington counties.

An Albany National Weather Service meteorologist measured an astounding 22" of snow in Schenectady in six hours between 2 and 8am Thursday morning. I measured an equally astonishing 25" of snow in Clifton Park in the same time period. That's six consecutive hours of 2.5" to 3" per hour snowfall rates, which is extraordinary.

Storm Statistics for Albany 

The "Mega" snow band, depicted on the two Albany Doppler Radar Images below, (the bright yellow zone,) extended from parts of eastern Otsego and northern Delaware counties through eastern Montgomery, Schenectady, central and southern Saratoga, southern Washington and northern Bennington counties Thursday morning December 17, 2020. You can see between about 4:45am and 5:45am there was almost no change in the position. Snowfall rates of 3"-4" per hour and up to 5"-6" per hour were occurring at this time in this zone with the band sitting on this area for several hours. Smaller scale transient banding is also evident on this image from the Capital Region on south and into the Berkshires with those smaller bands feeding north into the "Mega" band.

Position of the Mega snow band at around 4:45am Thursday December 17, 2020

Position of the Mega snow band at around 5:45am Thursday December 17, 2020 

WeatherNet 6 December 16-17, 2020 observed snowfall and distribution Map. The extraordinarily intense qusi-stationary mesoscale snow band, with the snowfall rates of 3" per hour and up to 5"-6" per hour, was observed between 2 and 8am with the band continuing, although weakening across Saratoga Washington, northern Bennington and southern Rutland counties through 10-11am Thursday December 17, 2020 with the storm generally over throughout the region by noon. The result was the swath of 24"-30" of snow with up to 35"-44" observed from north central Pennsylvania, through the Binghamton area, then locally cutting across portions of Otsego and Delaware counties, through Schoharie County, the eastern Mohawk valley, Glens Falls-Saratoga-northern Capital Region, Washington County, southern Rutland and northern Bennington counties then east into central New Hampshire. The snowfall gradient into and out of this zone was in many areas about 1" per mile which is very tight.

WeatherNet 6 observed snowfall amount and distribution Map - December 16-17, 2020 

National Weather Service Generated Map illustrating the zone of observed extreme snow accumulations across New York

WeatherNet 6 observed snowfall amount and distribution Map - December 16-17, 2020 

A sampling of some of the top snowfall amounts reported by WeatherNet 6 spotters locally. The current Vermont state 24 hour record snowfall is 42" at Jay Peak set on February 5, 1995. The Landgrove, VT measurement, if verified, would tie that with a National Weather Service cooperative observer in Peru, VT coming in with 44.8". If this Peru measurement is verified that will become the new record 24 hour snowfall for the entire state of Vermont.

Some WeatherNet 6 top observed snowfall amounts - December 16-17, 2020 

Other Storm Records across the Northeast

Some WeatherNet 6 top observed snowfall amounts - December 16-17, 2020 

The Storm
Just about every aspect of this event from the meteorological parameters that created it, to its behavior, the extreme snowfall it produced in such a short period of time, and its overall impact, can by far and away be classified as rare and at the upper end of the extreme. This, despite the area of low pressure itself, not being particularly intense (around 995 mb,) as winter storms go, or rapidly intensifying, which typically are traits we (meteorologists) look for when diagnosing heavy snowfall potential from a system.

In this case, however, a strong (1040mb) cold high pressure system, which was centered just north of New England, in the text book position for a major Northeast snow storm, was likely more important than the nor 'easter itself as the pressure gradient between the two in the moisture feeding levels of the atmosphere became intense, due in part to the strength and configuration of the high. The resultant flow subsequently transported a rich supply of water vapor into the Northeast, and continually replenished it through the event. The graphic below is a computer model forecast depiction of the moisture source, a broad atmospheric river originating in the Pacific and crossing the Gulf of Mexico, then up the Atlantic seaboard, and the strong pole ward transport of that water vapor into the Northeast.

Comoputer model forecast of integrated water vapor transport at 2am Thursday December 17, 2020

So, the moisture was extreme, with subsequent liquid equivalent measurements from the storm locally ranging from 1.50" to 3.00" (2.00" at Albany.) Liquid to snow ratios, which were forecast to be as high as 15:1 (1" of liquid = 15" of snow) were actually in the 10:1 to 12:1 range which still resulted in a very dry, light fluffy snow as surface temperatures ranged through the mid and upper teens (a very cold storm) throughout the region during the event.

In addition to extreme moisture, the resultant vertical velocities (lifting) over what can be described as an elevated warm front, or frontogenesis region, in the atmosphere also became extreme in this event with that rapidly rising air, intersecting a region of the atmosphere where temperatures ranged from -12 to -18 degrees C (optimal snow growth temperatures for dendrites, which effectively accumulate) creating a scenario for intense snowfall rates in small scale banding in and northwest of the frontogenesis area. Aiding in the rapid ascent was the presence of the left exit region of a strong upper level jet (this produces a rising transverse vertical circulation in the atmosphere)

4am 3KM NAM depiction of the region of intense frontogenesis

WeatherNet 6 observed snowfall amount and distribution Map - December 16-17, 2020

From a forecast standpoint, it was clear days in advance that a major snow storm for parts of the Northeast was possible with the likelihood increasing as the event neared and as such was well forecast. Timing, which is often tricky, was also very well forecast as was temperature with the accurate forecast of a dry fluffy snow. So, those more broad aspects of the forecast for the region worked out quite well.

The forecast problems, however, were in being able to precisely determine the small scale snow banding placement and intensity of the snow in those bands as well as duration of heavy snow at any one location. Accurately predicting those factors is very difficult, partially due to small scale nature of banding elements embedded within a larger synoptic scale system. We (meteorologists) do not have a lot of skill at this point in forecasting well in advance of an event with much precision where a mesoscale snow band or bands will set-up, what the ultimate snowfall rates in them will be, and how long they'll last over any one area. This case was no different.

We do have computer models, though, which offer guidance as an aide, but often, and in particular with this case, will paint a wide range of possible solutions. The wider the range of solutions, the greater the uncertainty in the outcome of an event. In this case those solutions suggested top snowfall amounts up to about 30", but also suggested 0" as a viable option as well. And as for banding placement, which is tied to storm track and the ultimate position of the low, the majority of the most reliable guidance fairly consistently favored the most pronounced banding to evolve over the southern half of the region, not the north. In the end, the placement error was only about 50-75 miles farther north from what was forecast, which in the grand scheme is not that large an error. But, when the margins between not much snow and huge amounts of snow are as tight as they are in banding scenarios, that amount of error has a huge impact on blowing up a forecast. I will say though, that the uncertainty in band evolution and behavior was conveyed in the forecast with an indication that a more northward solution in band positioning was at least possible. In the end, however, It did not become apparent until the storm was underway that a more northward evolution of banding was going to occur.

The other significant forecast problem was being able to accurately predict maximum snowfall rates in the bands as well as duration of intense snowfall at any one location, both challenging on the best of days. In this case, snowfall rates of 2"-3" per hour were predicted in advance of the storm, which is pretty good. Maximum snowfall rates, however, were calculated to have been as high as 5"-6" per hour in the "Mega" band which is astounding and something I've only seen once locally in the 2007 Valentine's day storm in areas west of the Capital Region. Snowfall rates that high are rare and therefore something that's unlikely we would currently be able to well predict.

And it wasn't just the "Mega" band that formed, the pre-dawn and early morning period on Thursday December 17 was characterized by a "Banda-Palooza" as multiple laterally translating smaller scale intense snow bands and bandlets with snowfall rates up to 2" per hour developed throughout the Catskills, mid Hudson valley and Berkshires which subsequently fed into the main mesoscale band as they lifted to the north into it. These smaller bands further south resulted in widespread 12"-18" snow accumulations in the mid Hudson valley to Berkshire County.

The radar image below shows the "Mega" snow band across the northern part of the region (the zone of yellow) with smaller scale heavy snow banding widespread across the Catskills, mid Hudson valley Berkshires and southern Bennington County, VT at 3:45am (the zones of darker green.)

Position of the Mega snow band and smaller scale bands to the south at around 3:45am Thursday December 17, 2020 

This is an event that will be studied for some time by the academics with everything new learned integrated into the tools we use to forecast the weather. Ultimately, it's events like these that go a long way into furthering our understanding of how the atmosphere works. And it's clear there is much we still do not know. But ultimately, what we learn will help to improve both forecasting as well as the communication of that forecast.

In my case, some lessons here are to perhaps be much less precise in forecasting snowfall amounts and placement of those amounts on the map in cases when uncertainty is high. Very large and broad ranges may be a better way to go, than my typical attempts at being as precise as I'd like to be. Also, better communication of the uncertainty, although it is my experience that very few pay attention to those explanations. In the end, a major snow storm was forecast for the entire region and it was forecast well in advance. The entire region got a major snow storm and got it within the period that was forecast, which was good.
What was not good was that snow amounts were over forecast slightly for the southern half of the local area and dramatically under forecast for the northern part.

Deep snow in Clifton Park Thursday morning December 17 - 30" measured Near Grooms and Vischer Ferry Rd.

Deep snow in Clifton Park Thurdsay morning December 17, 2020

Deep snow in Clifton Park Thurdsay morning December 17, 2020

Deep snow in Clifton Park Thurdsay morning December 17, 2020 

The Role of Climate Change in Blockbuster Snowfalls
Data analysis is showing an increasing impact of climate change on the behavior of snow storms with studies indicating a longer term diminishing trend in the number of large storms that occur overall, but an increasing trend in the amount of snow that is produced in those large storms when they do occur. This is largely being attributed to a combination of warmer oceans and a warmer atmosphere. For every 1 degree C increase in air temperature you can pack an additional 7% of water vapor into the atmosphere meaning a warmer atmosphere leads to wetter and in the case of winter, if it's cold enough, snowier storms.

The image below is the December 18, 2020 NOAA sea surface temperature anomaly graphic. It shows much warmer than average sea surface temperatures from the mid Atlantic coast all the way up through and beyond New England for this time of the year. So, this warmer ocean would contribute additional moisture to the atmosphere giving our storm more to work with and allowing for perhaps heavier accumulations of snow to occur than if this very same event would have happened thirty years ago. I certainly cannot say this with certainty for this case unless a specific attribution analysis was done on this storm to show it. But, the conceptual model does support the premise and the data is showing blockbuster snowfalls occurring with increasing frequency locally when those larger storms happen.

December 18, 2020 NOAA analysis of sea surface temperature anomalies 

Anecdotally we can take a look at Albany's top 10 single storm snowfalls by month lists which does show an increasing number of top 10 snowfalls occurring at an increasing frequency. Just since 2000 there have been 12 record top 10 single storm snowfalls at Albany, 1 in November, 4 in December, 3 in January, 1 in February, 2 in March, and 1 in April. Our partners at Climate Central did an analysis and found that 43% of all two day snowfall records set nationally have occurred since 1980 clearly showing the upward trend. Climate change is increasing snowfalls from big storms in the winter.

Climate Central analysis of increasing 2 day record snowfalls since 1980 nationally

WeatherNet Storm Total Snowfall Reports Thursday-Friday December 16-17, 2020

(Note: Reports with an * notation are NWS relayed and not WxNet 6 spotter observations)

Town County Snowfall Report Town County Snowfall Report
Savoy, MA Berkshire 23.3" Canaan, CT Litchfield 16.0"
Becket, MA Berkshire 14.0" Pittsfield, MA Berkshire 14.5"
Great Barrington, MA Berkshire 13.7" Hancock MA Berkshire 16.0"
Clarksburg, MA Berkshire 15.5" Stockbridge, MA Berkshire 12.4"
Albany (ASOS)* Albany 22.9* Delmar Albany 22.0"
Rensselaerville Albany 30.0" Berne Albany 26.0"
Knox Albany 29.5" Albany (NWS)* Albany 25.2"
Cohoes Albany 24.0" Guilderland * Albany 23.0"
Livingston Columbia 17.0" Taghkanic Columbia 13.8"
Ancramdale Columbia 14.8" to 16.0" Germantown Columbia 16.5"
Spencertown Columbia 18.0" Chatham* Columbia 12.5"
Austerlitz* Columbia 13.5" Valatie* Columbia 16.0"
Roxbury Delaware 17.4" Margaretville Delaware 18.0" to 24.0"
Fleischmanns* Delaware 17.4"      
Pine Plains Dutchess 14.0" Red Hook* Dutchess 20.0"
Staatsburg Dutchess 17.0" Millerton* Dutchess 23.0"
Poughkeepsie* Dutchess 15.0" Millbrook* Dutchess 14.5"
Stratford Fulton 24.0" Johnstown Fulton 26.0"
Perth Fulton 29.0" Northville Fulton 19.2" (Not Total)
Greenville Greene 27.5" Halcott Center Greene 21.0"
South Cairo Greene 25.0" Cairo Greene 16.0"
Earlton Greene 25.0" West Kill Greene 20.8"
Haines Falls Greene 16.5" Catskill Greene 15.8"
Wells Hamilton 22.0" Piseco Hamilton 14.0"
Indian Lake Hamilton 4.0" to 6.0" Lake Pleasant* Hamilton 13.8"
Hoffmeister* Hamilton 11.0"      
Fonda Montgomery 19.5" to 20.0" Amsterdam Montgomery 30.0"
Tribes Hill Montgomery 22.0" Palatine Bridge Montgomery 20.0"
Glen Montgomery 28.0" St.Johnsville* Montgomery 16.8"
Hessville Montgomery 14.0" Fort Plain* Montgomery 14.7"
Oneonta Otsego 25.0" East Worcester Otsego 32.0"
Schenevus* Otsego 27.0" Cooperstown* Otsego 19.0"
Center Brunswick Rensselaer 20.0" Castleton Rensselaer 19.0"
Hoosick Falls Rensselaer 20.0" Petersburg Rensselaer 18.0"
Brunswick Rensselaer 24.0" Speigletown Rensselaer 25.0"
North Greenbush Rensselaer 22.0" Troy* Rensselaer 19.1"
Galway Saratoga 29.0" Lake Desolation Saratoga 29.5"
Malta Saratoga 26.0" Corinth Saratoga 30.0" to 31.5"
Clifton Park (Oaks) Saratoga 30.0" Clifton Park Saratoga 27.5"
Ballston Spa Saratoga 28.0" to 30.0" Saratoga Springs Saratoga 27.0" to 30.0"
Charlton Saratoga 31.0" Gansevoort* Saratoga 35.0"
Wilton* Saratoga 34.1" Round Lake* Saratoga 34.0"
South Glens Falls* Saratoga 25.0" Mechanicville* Saratoga 21.0"
Delanson Schenectady 29.0" to 31.0" Duanesburg Schenectady 29.0"
Glenville Schenectady 29.0" Rotterdam Schenectady 28.0"
S. Schenectady* Schenectady 31.0" Scotia* Schenectady 30.7"
Niskayuna* Schenectady 30.2"      
Schoharie Schoharie 30.0" Charlotteville Schoharie 30.0"
Conesville Schoharie 30.0" Richmondville Schoharie 30.0"
Warnerville Schoharie 26.5" Huntersland Schoharie 31.0"
Jefferson Schoharie 31.0" Middleburgh Schoharie 28.0"
Cobleskill* Schoharie 24.0"      
Olivebridge Ulster 18.0" Phoenicia Ulster 19.0"
Esopus Ulster 12.0" New Paltz* Ulster 13.5"
Queensbury Warren 29.0" to 33.0" Glens Falls Warren 30.0"
Lake George* Warren 21.0" Warrensburg Warren 18.0"
Lake Luzerne Warren 16.0"      
Hebron Washington 40.0" Hartford Washington 30.3"
Hudson Falls Washington 24.3" Granville Washington 35.0"
Fort Ann Washington 24.0" Whitehall Washington 16.1"
Cossayuna Washington 35.0" to 39.5" Salem Washington 38.0"
Greenwich Washington 38.0"      
Landgrove, VT Bennington 42.0" Woodford, VT Bennington 30.0"
Manchester, VT Bennington 32.7" Stamford* Bennington 23.0"
Danby, VT Rutland 36.0" West Rutland, VT Rutland 22.0"
Peru, VT* Bennington 44.8" East Dorset,VT Bennington 39.0"
Wilmington, VT Windham 22.0"      

Albany NWS Snowfall Analysis December 16-17, 2020

Albany National Weather Service Snowfall Analysis December 16-17, 2020 

Heavy snow accumulation (22") in Delmar, Albany County
Thursday morning December 17, 2020
WeatherNet 6 Spotter Allen Landau

Delmar, Albany County Thursday morning December 17, 2020

Heavy snow accumulation (30") in Amsterdam, Montgomery County
Thursday morning December 17, 2020
WeatherNet 6 Spotter Dick Mucilli

Amsterdam, Montgomery County, Thursday morning December 17, 2020 

Heavy snow accumulation (31") in Charlton, Saratoga County
Thursday morning December 17, 2020
WeatherNet 6 Spotters Eric and Nancy Utermark

Charlton, Saratoga County, Thursday morning December 17, 2020 

Heavy snow accumulation (29") in Ballston Lake, Saratoga County
Thursday morning December 17, 2020
Brad Bowers

Ballston Lake, Saratoga County, Thursday morning December 17, 2020