Wednesday, November 15, 2017

Frequency of Snow

The scene in Fairbanks is wintry at last, with persistent light snow events in the past week bringing the snow depth up to 9 inches.  This is a little above normal for the time of year.

Beginning last Wednesday, 6 consecutive days produced measurable snowfall in Fairbanks; this seems a little unusual, but it's typical for a 6-day snowy period like this to occur at least once in a winter.  The record for consecutive days with measurable snow is 16 days in November 1994, and the next longest periods are:

14 days ending Oct 24, 1970
13 days ending Nov 24, 1988
12 days ending Jan 10, 1987
12 days ending Nov 8, 1996

It's a bit curious that prior to 1965 (i.e. 1930-1964), the longest streak of snowy days was only 10 days; but perhaps there was a tendency to overlook very small (e.g. 0.1") snow accumulations in the early years.

The fact that 3 of the longest 5 periods ended in November is consistent with the peak in daily snowfall frequency at this time of year.  The figure below shows a smoothed daily frequency of measurable snow (blue line) and also shows the frequency of snowfall when there was snow on the previous day (purple line).  As we would expect, the chance of snow is higher if the previous day was snowy.

Taking a quick look at webcams around the area, freeze-up is still not complete in Fairbanks, although the Tanana River at Nenana is ice-covered now.

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