Snow Depth Days
of the Northeast

This page has snow depth data for the winter of 2008-2009 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

The explosive start of the 2007/2008 season didn't happen this year. Still, December brought over two feet of snow in 9 days with snowy weather, with most falling between the 19th and 21st, but most melted just after Christmas. January brought two and a half feet with three storms over 6". For the season to date this was more snow than many years. Southern New England saw more snow than in all of last year. There was no January thaw, the high for the month was just 38 and the dew point never went above freezing. There was plenty of cold, the low of -17 was the lowest I've record (by 4 degrees) in my five years of records. February had near average temperatures, but much less snow than average, just under a foot. Still, the minimum snow on the ground was never less than a foot and the SDDs for the month exceeded the seasonal total for half the years in my record.

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
Ashland MA 26 86 21.5 172 7 72
Fairhaven MA 19.1 50 6.6 67 4.1 14 5.8 21
Groveland MA
Marlboro MA 29.7 78.5 22.9 246.5 6.3 158.5 12.3 46.5
Pepperell MA 0.2 0 30 118.5 28.1 379 9.2 349 18.3 132
Poland Spring ME 0.4 0 24.7 129 29.2 354 26.3 496
Bow NH 32.2 145 35.7 496 17.6 616 20.3 567
Penacook NH 26.1 111 30.6 376 11.3 488 12.8 307
Charlestown RI 17.4 44 17.2 132 3.6 44 11.6 34
Woonsocket RI 23.2 64 19.6 210 6.1 68 10.2 42
Mt. Mansfield VT 6 37 30.5 232 55.1 853 48.4 1601 31.5 2008 15.5 2458 21.5 2429 0 617

2008-2009 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 0 0 ...
Ashland MA 54.5 330 6.1
Fairhaven MA 35.6 152 4.3
Groveland MA 0 0 ...
Marlboro MA 71.2 530 7.4
Pepperell MA 85.8 978.5 11.4
Poland Spring ME 80.6 979 12.1
Bow NH 105.8 1824 17.2
Penacook NH 80.8 1282 15.9
Charlestown RI 49.8 254 5.1
Woonsocket RI 59.1 384 6.5
Mt. Mansfield VT 208.5 10235 49.1

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: 2009 December 13
Ric Werme

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