Interior Alaska and 2013 Daily Anomalies

As we have discussed several time in the last few months, 2013 was a very anomalous year for much of Alaska. Even though the annual temperature deviations were not too extreme in most cases, there were many, many days with large temperature deviations. One common method of measuring dispersion is to look at the distribution from an expected mean. Assuming temperatures are normally distributed, which they pretty much are, we would expect that 95% (95.4% to be precise) of days would be within 2 standard deviations of the daily mean. In other words, we would expect that 4.6% of days would be more than +2 standard deviations or less than -2 standard deviations from the daily normal.

In 2013, this was true for the vast majority of the U.S. To analyze this, I paired stations in the GHCN v.3 database with 1981-2010 daily normal values published by NCDC. For the Lower 48, I only used primary stations (n=866) and for Alaska I used both primary and Cooperative stations (n=103). In each case there had to be no more than 25% of days with missing or flagged data.

On the maps, anything shaded in blue indicates that less than 4.6% of days were more than 2 standard deviations from the daily mean. Yellow, orange, and red colors show areas that exceeded the expected rate of days that were more than +2 standard deviations or less than -2 standard deviations from the daily normal.Only a few areas in the Intermountain West and much of Alaska had significantly more than 5% of days greater than 2 standard deviations from the daily mean.

The 'Winner' for primary (USW) stations in the entire U.S. was Anchorage's Merrill Field with a value of 10.1%. The Delta 6N Cooperative station in Alaska actually had a value of 11.9%. Figure 3 shows the stations with the largest percentage of +/- 2 standard deviation days.

Figure 1. Percentage of days in Alaska more than +2 standard deviations or less than -2 standard deviations from the daily normal.

Figure 2. Percentage of days in the U.S. more than +2 standard deviations or less than -2 standard deviations from the daily normal.

Figure 3. List of stations ranked my the highest number of percentage of days more than +2 standard deviation or less than -2 standard deviations from the daily normal.