May 12th saw first 90-degree high temperature of 2022 in the Twin Cities, with May 28th doing it again. How unusual is it to have multiple 90-degree high temperatures in May in the Twin Cities, and does doing so mean we will have a greater-than-average number of 90-degree days during summer?
Although good hot days in May are pretty common, the Twin Cities has had two or more 90 F high temperatures during May less than a fifth of the time, historically. Those years have usually gone on to have above-average numbers of 90-degree days too.
Through 2021, 90-degree readings in the Twin Cities during May have occurred in 48 out of 149 years on record, or about 32% of the time. Only 24 years, or about 16%, have had two or more 90-degree days during May. Having three or more 90-degree F high temperatures is rare, occurring less than 5% of the time. May 1934 was by far the most extreme, with eight daily highs of at least 90 degrees, including a reading of 106 on May 31st. More recently, May of 2018 had a remarkable run of six straight days, including a 100 F reading on Memorial Day.
Over recent decades, and including the current "normals" period of 1991-2020, the Twin Cities area has averaged 13 days per year with a high temperature of 90 degrees F or higher. But years with two or more 90 F high temperatures during May historically have tended to finish with far more hot days, averaging over 23 for the season. In any case, 87.5% of those years the (21 out of 24) ended the year above the average of thirteen 90 F days, and 75% (18 out of 24) had at least 20 such days.
In other words, when we have observed multiple hot days in May historically, the year has usually gone on to produce more than the usual number of hot days also. Of course, this is not a prediction! It is only a statement of an apparently strong historical relationship between hot days in May and hot days during the rest of summer.
Below is a table comparing the number of 90 F high temperatures during May in the Twin Cities, with the total number recorded for the entire year.
Counts of 90-degree High Temperatures, Twin Cities May Annual Year Total Total --------------------------- 1934 8 34 2018 6 20 1874 5 26 1925 4 20 1987 4 24 1988 4 44 1911 3 16 1921 2 26 1931 2 30 1939 2 23 1949 2 33 1952 2 17 1959 2 29 1964 2 27 1969 2 12 1970 2 26 1972 2 11 1978 2 20 2001 2 20 2006 2 20 2007 2 27 2009 2 6 2010 2 17 2012 2 31 2022 2 ?? --------------------------- Average: 23.4
June 2, 2022