Temperature notebook: December 2021 one of Bloomington’s warmest on record

Sub-freezing temperatures in Bloomington on the second day of 2022 signaled a contrast between the last month of 2021 and the start to the new year.

The National Weather Service office for Indianapolis led off its Jan. 2 forecast like this: “The recent warm weather pattern has come to an end. Colder temperatures will persist through the upcoming week.”

What did the “recent warm weather pattern” mean for Bloomington?

December 2021 ranked fourth warmest as defined by the mean of the average daily temperature among all Decembers—since records started being kept by the Indiana University weather station in 1895.

It was a 42.2 F degree average for December 2021 that put it in fourth place.

To find first place for that statistic, you have to look almost a hundred years into the past: In 1923 the average of the mean daily temperature was 43.5 F degrees.

But December 2021 ranked warmest when defined as the number of days when the mercury topped 60 F degrees for the month. On 11 days in December 2021, the temperature reached more than 60 F degrees.

Second place on the list is 1946, when the temperature reached more than 60 F on 10 days in December that year.

When the book was closed on Bloomington’s temperature readings for 2021, just two daily extremes had been achieved.

One was a record for the daily low for May 7, which was 28 F degrees. The other was a record for the daily high for Dec. 26, which was 65 degrees.

Because the daily 24-hour period for the IU Bloomington weather station runs from 7 a.m. to 7 a.m., not midnight to midnight, that Dec. 26 high can be considered as a Christmas Day record high temperature.

Bloomington Indiana IU Campus Station: ACIS NOAA Regional Climate Centers

Days Max Temp >= 60
Year Dec
2021 11
1946 10
1982 9
1900 8
1933 8
1932 7
1971 7
1984 7
1923 6
1962 6
1998 6
1918 5
1922 5
1931 5
1941 5
1949 5
1951 5
1970 5
2015 5
2019 5

Bloomington Indiana IU Campus Station: ACIS NOAA Regional Climate Centers

Monthly Mean Avg Temp
Year Dec
1923 43.5
2015 43
1931 42.3
2021 42.2
1982 41.5
1971 40.9
1918 40.8
1984 40.8
1965 40.1
1957 39.8
1946 39.7
1940 39.5
1941 39.5
1933 39.4
1949 39.3
2012 39.2
1959 39
1994 38.8
1998 38.5
1964 38.4

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