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Cold Winters in Boulder

As we did with hot summers, we consider several measures of winter weather. First, does cold weather sometimes arrive early, so that the average temperature over the December-February period is lower than that in calendar winter (Dec 21 - March 21)? Then, there's the measure of the number of very cold days, which we define as minimum temperature below 10 degrees. The table below compares the coldest winters by each of these measures. We found that the June-August period in the hottest years had about the same average temperature as the summers of the hottest years by that measure. In contrast, the calendar winter is substantially colder than the December-February period.

Year
Dec-Feb Avg
Year
Winter Avg
Year
10-deg Days
1955
22.2
1942
17.0
1932
32
1973
32.2
1937
18.8
1962
30
1942
32.6
1940
19.3
1973
29
1937
32.7
1949
20.1
1942
29
1941
32.8
1962
20.4
1949
28
1993
33.3
1978
20.5
1984
27
1944
33.4
1948
20.7
1937
27
1991
33.6
1985
20.8
1996
26
2001
33.7
1947
20.9
1947
26
1985
33.8
1944
21.0
1936
26

Of course, it's also interesting to see which were the warmest winters by the same measures. The table below provides those comparisons. Although we sometimes complain about "early winter" when we get some cold days in early December, it's clear from these two tables that the first part of March, on average, is several degrees colder than the first part of December. Note that 2000 was the only year to make the 10-warmest list in all three categories.

Year
Dec-Feb Avg
Year
Winter Avg
Year
10-deg Days
2000
44.0
1972
40.0
2000
1
2004
42.8
2000
39.4
1958
4
1972
42.1
2004
37.2
1961
4
1976
42.0
1956
36.6
1981
4
1956
41.9
1976
36.3
1983
5
1964
41.4
1952
36.1
1944
6
1996
41.3
1968
35.6
1998
6
1934
41.0
1964
34.8
1934
7
1968
40.8
1996
34.6
1935
7
1952
40.7
1980
34.6
1992
7

Finally, we have a graph of the number of 10-degree days, with the different measurement locations noted. Each point represents a winter that includes parts of two calendar years. That is, the 2006 value includes the period September 2005 through April 2006. It's interesting to note that the number of 10-deg days didn't vary much with location until the station was moved to the NIST grounds. The NIST campus is closer to the base of the Flatirons and at somewhat higher elevation than the earlier measurement sites. Much of the difference may be due to being slightly above the coldest part of the inversion layer that is often present on cold days.

 

B.C.N.A.
P.O. Box 493
Boulder, CO
80306