Early-Season Heat Waves

Heat extremes often punctuate Minnesota's summers, and are most common from the end of June through the end of August. July is by far the state's hottest month, boasting virtually all of our statewide and station-specific heat records, and historically accounts for 40% of all 90-degree F days.

Heat waves that occur during or before the first half of June are less common, and often of a different nature than many (though not all) mid-summer heat waves. A typical July or early-August heat episode may be oppressively humid, whereas late-spring episodes tend to be somewhat "dry."

The worst heat wave on record in Minnesota occurring any time through the first half of June was from June 3 to June 11, 2021. This event demolished daily and early-season temperature records in northern Minnesota initially, and dealt record or near-record warmth to southern and central Minnesota for nine unrelenting days, when the temperature never fell below 70 F in the Twin Cites, and when many locations soared into the 90s or even 100s each afternoon.

Following are some statistics from the Twin Cities historical record, for heat extremes occurring on or before June 15th. Keep in mind, a heat wave is not only defined by the daily high temperatures, but also by warm nights. Some of late spring and early summer's hottest days have had tolerably mild nights, thanks to the dry air in place. Any time the high tops 90 F and the low also tops 70 F, however, the body will struggle to cool itself, day or night.

 

Highest daily temperature recorded in Twin Cities on or before June 15
Rank Temperature (F) Date Remarks
1 106 May 31, 1934 Highest temperature recorded outside of July
2 103 June 7, 2011  
3 102 June 8, 1985  
4 100 May 28. 2018 Earliest occurrence (in season) on record
- 100 June 13, 1956  
6 99 June 5, 2021 Most recent occurrence
- 99 June 13, 1987  
- 99 June 10, 1956  
- 99 May 22, 1925 Earliest occurrence (in season) on record
10 98 May 14, 2013 Earliest occurrence (in season) on record
- 98 June 14, 1987  
- 98 June 10, 1973  
- 98 May 30, 1934  
- 98 May 28, 1934  
15 97 June 10, 2021  
- 97 June 4, 2021  
- 97 June 6, 2011  
- 97 May 19, 2009  
- 97 May 28, 2006  

 

Number of 90 F (or greater) high temperatures through June 15 in Twin Cites
Rank Year Number of 90 F Highs
1 1934 12
2 1988 11
- 1987 11
4 2021 10
5 2007 8
- 1976 8
7 2018 7
- 1959 7
- 1952 7
- 1925 7
11 1956 6

 

Runs of five or more consecutive days with 90+ F high temperatures, occurring on or before June 15, in Twin Cities

Dates Number of Consecutive 90+ F Days Highest Temperature (F) Average Daily Maximum Temperature During Streak (F)

Average Daily Mean Temperature  During Streak (F)

Remarks
June 3 - 11, 2021 9 99

95.0

84.8 Longest and warmest early-season streak
May 24 - 29, 2018 6 100 93.5 81.0 Earliest streak (in season) and earliest 100 F reading on record
May 28 - June 1, 1988 5 92 91.2 73.2  
May 28 - June 2, 1934 6 106 94.0 82.3 Highest temperature ever recorded outside of July
June 9 - 14, 1956 6 100 95.5 82.8 Highest average daily maximum temperatures
June 11-15, 2007 5 92 91.0 80.0  

 

Highest daily minimum temperature (that is, the "highest low temperature") recorded in Twin Cities on or before June 15
Temperature (F) Date Remarks
78 June 5, 2021 Earliest occurrence (in season) on record
78 June 7, 2011  
77 June 8, 2021  
77 June 10, 2017  
77 June 13, 1956  
76 June 6, 2021  
75 June 10, 2021  
75 June 9, 2021  
75 May 28, 2006 Earliest occurrence (in season) on record
75 May 31, 1934  
75 June 5, 1925  
74 June 7, 2021  
74 June 8, 2020  
74 May 29, 2006  
74 June 11, 1956  
74 June 6, 1925  
74 May 22, 1921 Earliest occurrence (in season) on record

 

Longest runs of consecutive low temperatures at or above 70 F recorded in Twin Cities occurring on or before June 15 in the Twin Cities
Dates Number of Consecutive 70+ F Lows Highest Minimum (low) Temperature (F) Average Daily Minimum Temperature During Streak (F)
June 3 - June 10, 2021 9 78 74.6
June 7 - June 9, 1959 3 73 71.3

 

Many of the above tables focus on "streaks" of consecutive days at or above certain temperature thresholds. However, these sorts of measures do not capture everything. One notable early-season heat wave not listed above occurred June 6 to June 14, 1976, when 8 out of 9 days produced a high of at least 90 degrees F in the Twin Cities. The average high during this period was 91.8 F, and the average daily mean temperature was 79. 1 F, meaning in many ways this event rivaled others listed above. Furthermore, it is doubtful that anyone at the time mistook the 88 F reading on June 10th for the heat "breaking!"

 

Last modified June 23, 2021

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