Snow Depth Days
of the Northeast

This page has snow depth data for the winter of 2006-2007 at sites around New England and New York. Data for previous years are available:

A summary of several years is on the homepage.

Snow Depth Days

Traditionally, a winter's snowfall has been tracked as simply the total snow that falls during the season. While fine for several purposes, it doesn't really measure the impact of the snow on people. Suppose the total snowfall for a season is 100 inches. Near a coast where the ocean brings in warm, moist maritime air and rain, snow may not last for very long. Inland where arctic air dominates, the snow will last longer and the maximum snow depth can be much greater than near the coast.

The type of snow also has differing impacts. A foot of dry, fluffy snow will compress quickly with time (or with more snow) whereas an equal depth of wet snow presents more challenges to driving, shoveling, compression and melting.

Snow Depth Days makes a better measure of impact a winter's snows. The depth days for a whole winter are simply the sum of the snow depth on the ground for each day of the winter. Storms that start with snow and change to rain count for less than storms that are all snow.

Two major blizzards in Massachusetts show the importance of the depth day metric. If you experienced both the Blizzard of '78 and the April Fool's Blizzard of '97, the 1978 storm wins hands down despite surprisingly similar snow distributions.  The key differences were the winds (1978 saw major coastal destruction), the weight of the snow (1997 took a heavier toll on tree limbs), and how long the snow remained. Massachusetts was shut down for a week in 1978, but the 1997 snow melted in days. 1997's storm brought far fewer depth days. On, Jan 20, 1978 a storm left 22" of snow in Boston, a January record and 24 hour record. While a rain storm on Jan 26 melted most of the snow in Boston, snowbanks were still on the sides of the streets and sidewalks when the second storm hit on Feb 6th setting new 24 hour (23.6") and total storm records (27.5"). Boston and much of the rest of state simply had no place to put the new snow. Those were the bulk of the snow that year, it would be fun to go back to the climatic records and compute the depth days for each month in 1978 and 1997.

Persistence Quotient

After tracking depth days for a few years, Jim Corbin realized that dividing a season's depth days by the season's snowfall, you get another interesting metric. The quotient is a number that tells you how many days an average inch of snow lasts. If two sites have the same number of depth days but a very different persistence quotient, the one with the higher value was colder than the one with the lower quotient. It didn't snow as much, but what fell stayed longer. I think depth days is the more important metric, but it's easy and worthwhile to track persistence too. Maybe we can find a correlation between it and average temperature.

The season in review

This season got off to a late start with a very warm November. The first measurable snow was on December 9th - 0.1". A flake or two less an I'd have called it a trace. The previous day Penacook had snow cover for was March 5th - 279 days earlier. (In 2002, we had snow on May 18, and the next season began October 23, only 189 days later!) December was also warm, closing out a year with no sub-zero days. However, last winter had two sub-zero days in mid-December. January started warm with a 68 degree high on the 6th, but the second half nearly brought the month to average with a high of only 7 on the 26th. Snow continued to be scarce, and most of the depth days for the month due to a 1" sleet storm capped with ice. Three sub-zero days in January meant that despite 2006, winters have continued to have sub-zero weather. Some snow fell in February, mainly in a 9" storm mid-month. At the end of "meteorological winter" (Decemeber, January, and February), many stations had posted near record setting low snowfalls.

March was weird. Penacook saw four sub-zero days. Three were the coldest lows of the winter and the fourth occurred without radiational cooling. That day Pepperell MA had a daytime high of only 12.5 (it was 15 at 0000), the coldest March 6th in 25 years of record keeping. March was also the snowiest month of the season, and combined with three snowfalls in April most stations wound up with total snowfalls and SDDs closer to average than anyone expected at the start of March. Many stations had more snow in April alone than the total up to the end of January! Penacook had totals very similar to 2005/2006, some other stations had significantly more, some had significantly less.

Daily/Monthly Data

The following table summarizes the snow fall and depth days from sites that are posting that data on local weather observations mail lists and a couple others. If people also prepare Web pages for daily information for their site, I'll include links to them. Cells under the "snow" column are the snowfall for the site in that month, under "SDD" are the depth days for the month.

Location October November December January February March April May
Snow SDD Snow SDD Snow SDD Snow SDD Snow SDD Snow SDD Snow SDD Snow SDD
Collinsville CT 1.5 2 14.9 109 12.8 134 0.5 0
Ashland MA 0.4 0 1.8 1 11.1 66 13.8 57
Fairhaven MA 1 1 1.3 1 5.1 9 5.7 5
Groveland MA 2.3 5.2 0 3.2 0 177.1 0 168.7 0 9.7
Marlboro MA 2 1.5 12.8 91.5 15.5 89.5 2.2 1.5
Pepperell MA 0.8 1 3.6 14 15.6 139 20 131 9.9 10
Poland Spring ME 3.2 5 7.7 76 19.7 386 19.1 318 28.1 93
Bow NH 2.2 2 4.5 29 15.8 227 20.5 308 14.1 37
Penacook NH 2 1 2.8 19 15.2 156 16.2 158 12.3 20
Charlestown RI 1.2 0 0.2 0 7.3 9 5.4 12
Woonsocket RI 0.6 0 1 1 7.6 9 11.3 32 0.2 0
Mt. Mansfield VT 19.8 152 0.5 172 43.5 305 31.5 826 57.3 1699 34.5 2355 51 2360

2006-2007 season to end of last month

The persistence quotient is lower than the ultimate value if there is still snow on the ground at the site. This data will be updated each month.

Location Snowfall Depth Days Persistence
Quotient
Collinsville CT 29.7 245 8.2
Ashland MA 27.1 124 4.6
Fairhaven MA 13.1 16 1.2
Groveland MA 2.3 363.9 158.2
Marlboro MA 32.5 184 5.7
Pepperell MA 49.9 295 5.9
Poland Spring ME 77.8 878 11.3
Bow NH 57.1 603 10.6
Penacook NH 48.5 354 7.3
Charlestown RI 14.1 21 1.5
Woonsocket RI 20.7 42 2.0
Mt. Mansfield VT 238.1 7869 33.0

Contributors

Name Location
Dennis Bollea Fairhaven MA
A Cadoret Woonsocket RI
Wayne Cotterly Poland Spring ME
Paul Hansen Marlboro MA
Jim Hilt Bow NH
Andrew Plona Collinsville CT
Jot Ross Ashland MA
Chris Seeber Charlestown RI
Rick Tracy Groveland MA
Paul Venditti Pepperell MA
Ric Werme Penacook NH

Credits

Jim Corbin, a meteorologist from Rhode Island, proposed the concept of both snow depth days and the persistence quotient, but he didn't have good names for them.  After a bouncing around various ideas, I came up with Depth Days.  It seems to fit into colloquial speech well, e.g. "When mired in the Depth Days of February, she thought fondly of the Dog Days of August." Of course, none of us snow lovers would ever think that. I picked Persistence Quotient while putting this page together, we'll see how it wears with time.

Musings

I think depth days is a great statistic, and I'm surprised that it is catching on slowly outside of the NE Weather Spotters mail list. I never expected that the NWS would embrace it quickly, but I had hoped that TV meteorologists would start using it, in monthly summaries, if nothing else. It would be nice if ski areas would use it, but they may not wish to if they are not likely to be #1 consistantly. (And if only one area reports depth days, it would not be a good comparative statistic.) The University of Vermont has graphs of snow depths at Stowe through many seasons.

Last update: 2007 May 13
Ric Werme

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