Thursday, November 24, 2011

Recap of the November Cold Snap

The record setting cold snap of November 2011 is history. So, without the media hoopla, here’s what happened. It's important to emphasize that the "news" here is the early occurrence of the cold snap, rather than the absolute values of the temperatures. The exact same temperatures anytime between Thanksgiving and Valentines Day would be unexceptional.

The mean 500mb heights (30dm contours) for November 15-21 (courtesy of ESRL and NCEP/NCAR Reanalysis) show a classic pattern for cold weather in Interior Alaska, with a high over Chukotka and fairly low height northerly flow across most of mainland Alaska (I’ve added centers and arrows to indicate wind direction.

In the Fairbanks area, this was easily the coldest pre-Thanksgiving week of record. At the Airport, the lowest 7-day average temperature was -30.1F for November 15-21. The previous record was -26.5F was set November 7-13, 1989. For November as a whole, this was the third coldest event; November 24-30, 1909 and the same week in 1927 were colder.

Record lows were set at the Airport on six days (November 16th did not have a new record) and record low maximum temperatures were set November 16-19. The high temperature of -30F on the 17th is the second earliest high of -30F or lower in the winter (November 9, 1989 is the earliest). The low temperature of -41F on the 17th is the fifth earliest occurrence of -40F in the winter. Here's the plot of November record lows:

Elsewhere around the area, temperatures varied pretty much as is typical for this time of year. The average temperature for November 15-21 at the North Pole cooperative station was -37.7F, with six days with lows in the -40s and an absolute low of -49F on the 17th. At the other extreme, Keystone Ridge cooperative station, at 1600’ MSL, had an average temperature of -13.4F the same week and an absolute low of -28F on the 21st.

Most places with a long period of observations set six or seven daily records. Lowest temperatures for the cold snap include:

University Experiment Station: -41F
Eielson AFB: -41F
UAF West Ridge: -40F

As more cooperative info becomes available I'll update the extremes.

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