wed, 01-may-2013, 05:41
normalized temperature anomaly heatmap

I’m writing this blog post on May 1st, looking outside as the snow continues to fall. We’ve gotten three inches in the last day and a half, and I even skied to work yesterday. It’s still winter here in Fairbanks.

The image shows the normalized temperature anomaly calendar heatmap for April. The bluer the squares are, the colder that day was compared with the 30-year climate normal daily temperature for Fairbanks. There were several days where the temperature was more than three standard deviations colder than the mean anomaly (zero), something that happens very infrequently.

Here are the top ten coldest average April temperatures for the Fairbanks Airport Station.

Coldest April temperature, Fairbanks Airport Station
Rank Year Average temp (°F) Rank Year Average temp (°F)
1 1924 14.8 6 1972 20.8
2 1911 17.4 7 1955 21.6
3 2013 18.2 8 1910 22.9
4 1927 19.5 9 1948 23.2
5 1985 20.7 10 2002 23.2

The averages come from the Global Historical Climate Network - Daily data set, with some fairly dubious additions to extend the Fairbanks record back before the 1956 start of the current station. Here’s the query to get the historical data:

SELECT rank() OVER (ORDER BY tavg) AS rank,
       year, round(c_to_f(tavg), 1) AS tavg
FROM (
    SELECT year, avg(tavg) AS tavg
    FROM (
        SELECT extract(year from dte) AS year,
               dte, (tmin + tmax) / 2.0 AS tavg
        FROM (
            SELECT dte,
                   sum(CASE WHEN variable = 'TMIN'
                            THEN raw_value * 0.1
                            ELSE 0 END) AS tmin,
                   sum(CASE WHEN variable = 'TMAX'
                            THEN raw_value * 0.1
                            ELSE 0 END) AS tmax
            FROM ghcnd_obs
            WHERE variable IN ('TMIN', 'TMAX')
                  AND station_id = 'USW00026411'
                  AND extract(month from dte) = 4 GROUP BY dte
        ) AS foo
    ) AS bar GROUP BY year
) AS foobie
ORDER BY rank;

And the way I calculated the average temperature for this April. pafg is a text file that includes the data from each day’s National Weather Service Daily Climate Summary. Average daily temperature is in column 9.

$ tail -n 30 pafg | \
  awk 'BEGIN {sum = 0; n = 0}; {n = n + 1; sum += $9} END { print sum / n; }'
18.1667
tags: weather  temperature  SQL 
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