Snowy November

November was a remarkably snowy month in parts of the interior, with Bettles setting a new record for total November snowfall at 50.6".  This is only the second time that any calendar month has produced more than 50" of snow in Bettles; the record was 55.8" in January 1973.  In McGrath the monthly total was the second highest for November at 44.6".  The chart below shows the winter-to-date accumulation of snowfall in Bettles compared to the historical range; this winter is running at a record pace, although interestingly the snow depth of 19" is not much above the normal of 15" for this date - the melt-off in October had a lot to do with this.

In looking at the historical distribution of autumn and early winter snow in Bettles, I noticed a surprising absence of large outlier snow totals in October, especially considering how wet Bettles is compared to Fairbanks.  As the chart below shows, the distribution of total precipitation in Bettles is strongly skewed in both October and November, with quite a number of very wet months.  However, total snowfall shows remarkably little skewness in October (second chart below); only 5 Octobers have exceeded 21" of snow, which is the same as in Fairbanks over the same period, although Bettles is almost 50% wetter on average for the month.

The scatterplots below show the joint distribution of October precipitation and snowfall for Bettles and Fairbanks.  It's interesting to observe that Bettles shows a less good correlation, and in particular many of the largest precipitation totals have been associated with relatively modest snowfall totals.

The ratio of snowfall to precipitation provides another look at what is going on (see below): the wettest Octobers in Bettles reliably have low snow ratios, which implies that plain rain accounts for a significant fraction of the precipitation in these wet months.  In the 10 wettest Octobers since 1951, 49% of the precipitation fell on days with a snow/precipitation ratio less than 5.  However, in Fairbanks there are fewer very wet outliers, and the tendency for reduced snow ratios is not as evident; only 31% of the precipitation occurred on days with a ratio less than 5, for the 10 wettest Octobers.

We can conclude that Bettles is more prone to heavy rainfall events in October than Fairbanks, even though Bettles is more than 5°F colder on average, and normal daily mean temperatures are below freezing even by the first of the month.  I find this quite surprising.

The parallel charts for November show a much tighter relationship between precipitation and snowfall amounts, as expected, because rain becomes unusual in both locations in November.  Nevertheless, it's interesting to see that even in November, Bettles often sees a snow/precipitation ratio of 10-12 or less, suggesting wet snow, whereas Fairbanks rarely sees a ratio much below 15 as the snow is usually less dense.