90 Degree High Temperatures in May for the Twin Cities

May 24 saw the first 90-degree high temperature of 2018 in the Twin Cities, with May 29th marking the 6th day in a row to reach or exceed 90. 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?

90-degree readings in the Twin Cities during May have occurred in 48 out of 146 years on record, or about 33% of the time. Only 23 years, however, or about 16%, have had more than one 90-degree day during May. Of those years, May of 1934 was by far the most extreme, with eight daily highs of at least 90 degrees, including a reading of 106 on May 31st.

We find that years with multiple 90-degree days during May have tended to be followed by summers that also have relatively high numbers of 90-degree days. The Twin Cities airport averages about 13 90-degree days per year, and 26% of years historically have had 20 or more such days. For years with at least two 90-degree days during May, however, the average number of 90-degree days for the year jumps to 23.4 (an 80% increase), and 74% of those years go on to have at least 20 90-degree days.

 

Counts of 90-degree High Temperatures, Twin Cities
May       Annual
Year       Total      Total
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1934      8             34
2018      6             TBD
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
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Average:              23.4