Recap of the July 2011 Heat Wave...Observations and Records

Observed Highs and Heat Index Values

Temperature Records

Dewpoint and Heat Index Records

Heat Wave Summary

An upper level high pressure system that had been over the Southern Plains and Southeast region of the U.S. during the first half of July shifted northwest into the Central Plains and Upper Midwest on July 16th and 17th.  Simultaneously the ridge strengthened, producing an expansive area of heat that extended into the Upper Mississippi River Valley region.  In addition, the combination of recent rains and release of water into the air by corn and soybeans caused dewpoints to increase to near record or record levels, making it feel very humid. The result was a 4 day stretch between July 17th and July 20th where max heat indices (what the temperature actually feels like) ranged between 100 and 120 degrees.  Also, the high dewpoints allowed for multiple new records to occur for warm low temperatures. The heat wave came to an end during the morning hours of July 21st, when a weakening cold front crossing the region helped usher in drier and slightly cooler air.

Observed High Temperatures and Highest Heat Index Values

Below is a listing of high temperatures and the highest heat index value for each day during the heat wave.

 

Saturday
July 16

Sunday
July 17

Monday
July 18

Tuesday
July 19

Wednesday
July 20

City/State

High Temp

Max Heat Index

High Temp

Max Heat Index

High Temp

Max Heat Index

High Temp

Max Heat Index

High Temp

Max Heat Index

Dodge Center, MN

82

91

86

99

88

105

90

108

88

100

Austin, MN

90

105

91

111

93

121

93

121

93

111

Rochester, MN

87

100

91

108

94

118

94

112

91

105

Winona, MN

88

98

93

108

93

114

91

111

93

103

Preston, MN

M

M

M

M

92

109 

94

108

92

99

 

 

 

 

 

 

 

 

 

 

 

Charles City, IA

 88

105 

91

111

93

117

93

117

91

108

Decorah, IA

90

100

93

105

93

111

97

114

93

103

Dubuque, IA

86

92

92

105

94

109

97

114

96

105

 

 

 

 

 

 

 

 

 

 

 

Medford, WI

82

89

91

111

91

108

86

99

91

105

Black River Falls, WI

86

95

93

110

91

111

91

102

95

108

La Crosse, WI

 88

 95

 96

 113

95

113

93

109

98

107

Sparta, WI

 88

 95

 94

 106

92

108

91

103

M

M

Volk Field, WI

 86

 95

 93

 111

91

114

91

108

95

107

Viroqua, WI

 85

 94

 92

 108

92

109

M

M

M

M

Prairie du Chien, WI

 89

 99

 94

 108

96

114

94

116

96

103

Boscobel, WI

 90

 99

 98

 114

100

117

97

114

101

109

Platteville, WI

 84

 90

 90

 103

91

108

93

105

91

101

City/State

High Temp

Max Heat Index

High Temp

Max Heat Index

High Temp

Max Heat Index

High Temp

Max Heat Index

High Temp

Max Heat Index

Missing Observations noted by M in the table above:

  • Preston, MN was not available over the weekend
  • Viroqua, WI was not available for July 19th and 20th
  • Oelwein, IA was not available and not included in the table
  • Sparta, WI was not available for July 20th.


Temperature Records for Rochester, MN and La Crosse, WI

Here is a listing of new records that have been established at Rochester, MN and La Crosse, WI during this heat wave:

Rochester, MN:

  • July 17th...Record warm low temperature of 77, breaking the previous record of 76 set in 1942
  • July 18th...Record warm low temperature of 79, breaking the previous record of 75 set in 1942
  • July 19th...Record warm low temperature of 76, breaking the previous record of 74 set in 1957
  • July 20th...Record warm low temperature of 76, breaking the previous record of 75 set in 1932
  • Consecutive 4 day warm low temperature of 77 between July 17th and July 20th, breaking the previous record of 76 degrees set between July 1st and 4th of 1911.

La Crosse, WI:

  • July 18th...Record warm low temperature of 80, breaking the previous record of 78 set in 1986.  Note that this is only the sixth time that a low of 80 degrees or higher has occurred.
  • July 19th...Record warm low temperature of 79, breaking the previous record of 77 set in 1977. 
  • Consecutive 3 day warm low temperature of 79 between July 17th and July 19th, breaking the previous record of 78.3 degrees between August 5th and 7th of 2001, and also June 28th and 30th of 1931
  • Consecutive 4 day warm low temperature of 78.5 between July 17th and July 20th, breaking the previous record of 77.8 degrees between August 5th and 8th of 2001.


Dewpoint and Heat Index Records for Rochester, MN and La Crosse, WI

EXTENSIVE HEAT WITH HIGH DEW POINT AND HEAT INDEX VALUES HAVE BEEN
COMMON THE PAST FEW DAYS ACROSS THE UPPER MIDWEST. ALTHOUGH THESE
TYPES OF RECORDS ARE NOT WELL KEPT...HERE IS SOME RECORD INFORMATION
WE WERE ABLE TO DISCERN FROM THE CLIMATE DATABASES. DATA IS ONLY
VALID FROM 1948 ON...

** DEW POINT RECORDS (DEG F) **

LA CROSSE WI

85     JUN 27 1934
       JUL 21 1934
       JUL 18 1942
       JUN 26 1978
       JUL 5 1978
84     AUG 9 1998
82     JUL 13 1995
81     JUL 19 2011
       JUL 18 2011
       JUL 14 2010
       AUG 8 2001
       NUMEROUS OTHER DATES

ROCHESTER MN

83     JUL 18 2011 /NEW RECORD/
       JUL 19 2011 /NEW RECORD/
82     JUL 13 1995
       JUL 12 1995
81     JUL 14 2010
       JUL 21 1983

** HEAT INDEX RECORDS (DEG F) **

LA CROSSE WI

121    JUL 4 1977
119    JUL 30 1999
118    JUL 13 1995
117    JUL 31 2001
116    JUL 11 1980
       JUL 7 1980
115    AUG 6 2001
       JUL 25 1999
       JUL 14 1995
       AUG 16 1987

ROCHESTER MN

118    JUL 18 2011 /NEW RECORD/
113    JUL 11 1980
112    JUL 19 2011
111    JUL 13 1995

 



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