Here on Keystone, through Monday, October 3rd, there has been no freezing degree days (FDD) yet, which makes this the latest in the autumn we've gone with zero FDD. What is a freezing degree day? It's the sum of 32F minus the daily mean temperature. Like most degree day statistics, there are no negative values: if the mean temperature is above freezing, the FDD is zero.
However, there are only 16 years of obs here on the hill, and two years, 2001 and 2006, had only 1 FDD through Oct 3rd.
If we look at the Fairbanks data for FDD, it turns out that it is by no means unusual to go this late in the autumn without any FDD yet. In 2009, 1979 and 1943, there were no FDD until October 18th, and the record warm October 1938 had no FDD until the 27th.
This is not quite an apples to apples comparison; I'd expect Keystone Ridge to have earlier occurrence of FDD, but it's probably safe to say that the lack of freeze not yet terribly unusual. The current numerical guidance suggests though that it will be at least the weekend and probably longer, so the lack of freeze may become extreme.
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