Tag: averages

As we head into the last few weeks of summer, some people’s thoughts turn to early snowfall in the mountains, and this topic recently popped up with respect to Mt. Mansfield in the New England Regional Forum at American Weather.  Since I have all the raw snowpack data from the Mt. Mansfield co-op station downloaded from when I created the Mt. Mansfield 24” snowpack plot, I scanned through the September numbers back to 1954 to see what they revealed.  Because the collection of actual snowfall at that station can be a bit dicey, I first checked the snowpack data that I had, and found three occurrences of September snowpack at the stake:

Date                 Snow at the stake (in.)
9/15/1959          1
9/16/1986          4
9/17/1986          2

However, assuming they have historically been using the same practice of reporting the depth of the snowpack at the end of the day (~5:00 P.M. or so) as they do now, it was likely that there was overnight September snowfall that simply didn’t make it through the entirety of many warm, September days to be reported from the stake.  Therefore, I also checked the snowfall data, and found that indeed there are a fair amount of reports of September snowfall:

Date                 Snowfall (in.)
9/15/1959          1.00
9/24/1966          0.50
9/2/1967            0.30
9/25/1967          1.50
9/22/1976          1.00
9/28/1980          0.50
9/16/1986          4.00
9/24/1989          1.00
9/21/1991          1.00
9/28/1991          0.30
9/29/1991          1.00
9/30/1992          0.30
9/23/1998          0.30
9/30/2009          0.02

There are a few years with no data, but accumulating September snow does happen on Mt. Mansfield, at a rate of roughly a couple times each decade.  I’m not quite sure what was going on with the 2009 number, since one doesn’t generally report snowfall to the hundredths of an inch; perhaps they are reporting a trace on that one.  Not surprisingly, September snowfall is more frequent on Mt. Washington with a couple thousand feet of extra vertical – the September monthly average there is 2.2” inches, and the monthly maximum is almost 8 inches, so accumulating September snow is probably fairly common.

I also scanned the Mt. Mansfield data for August, and there was even one report of accumulation there:

Date                 Snowfall (in.)
8/28/1986          0.20

Since there was also mention of October, I took a look at those data as well.  Because accumulating October snowfall is already fairly common even down here in the mountain valleys of the Northern Greens (out of the six season’s worth of snowfall data I have collected here, four Octobers have seen accumulating snowfall, and the average is right around an inch) I figured that getting October accumulation on Mt. Mansfield must be almost a lock.  Indeed that’s the case; after checking the snowpack data from 1954 – 2012, there are only a handful of seasons without reported snowpack, and one of those seasons did at least show some snowfall:

Seasons without reported October snowpack on Mt. Mansfield
1956-1957
1963-1964 – 0.1” snowfall
1971-1972
1973-1974
1985-1986
1996-1997
2007-2008

So essentially it’s about twice a decade that there is accumulating snow on Mt. Mansfield in September, and about once a decade that there isn’t accumulating snow on Mt. Mansfield in October.