July 2011 Heat Wave

July 2011 Heat Wave...Observations and Records

Observed Highs and Heat Index Values

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