PRELIMINARY IOWA WEATHER SUMMARY – JULY 2012
General Summary. Iowa temperatures averaged 79.7° or 6.1° above normal while precipitation totaled 1.16 inches or 3.34 inches below normal. This ranks as the 3rd warmest and fifth driest July among 140 years of records. A hotter July was last recorded in 1936 and a drier one in 1975.
Temperatures. Temperatures averaged above normal on all but four days (10th-11th & 27th-28th) of the month. Daily readings were more than ten degrees above normal on the 3rd-6th, 17th-18th and 23rd-25th. Triple digit temperatures were recorded somewhere in the state on twelve days with Donnellson, Fairfield and Keokuk reporting the highest readings with 107° on the 23rd. The last time Iowa saw a 107° reading was on July 29, 1999 at Keosauqua while Sioux City was the last location to exceed this reading with 108° on July 12, 1995. Statewide there was an average of 21 days with daily high temperatures of 90° or higher with three of those reaching 100° or more. By comparison a typical year brings 23 days of ninety degree heat with one day reaching 100. At Atlantic, Creston, Mount Ayr, Osceola and Shenandoah there were only three days during the month that the temperature failed to reach 90. Des Moines, Keosauqua and Osceola recorded the most triple digit days with ten each. In recent years Iowa’s summer heat has been characterized by unusually high overnight lows thanks to higher humidity resulting from abundant rainfall. This month, however, daytime high temperatures averaged 7.9° above normal while nighttime lows were ‘just’ 4.3° above normal. Elkader reported the month’s lowest temperatures with 51° readings on the 11th and 12th.
Cooling Degree Days. Home air conditioning requirements, as estimated by cooling degree day totals, averaged 11% greater than last July and 69% more than normal. The year-to-date total is running 27% greater than this time last year and 66% more than normal. This season’s year-to-date total already exceeds the annual normal of 800 cooling degree days and is the highest year-to-date total since 1936.
Precipitation. Rainfall was below normal at all reporting points in the state. Totals varied from none at Underwood to 4.52 inches at Stanley. There were no widespread heavy rain events during the month with the largest daily event average of just 0.35 inch on the night of the 25th. Record low July rain totals were recorded at several locations:
City 2012 Total Old July Record Period of Record
Atlantic Trace 0.43 in 1975 125 years
Audubon Trace 0.32 in 1974 116 years
Logan 0.02 0.33 in 1936 146 years
Harlan 0.06 0.31 in 1959 113 years
Guthrie Center 0.12 0.15 in 1975 113 years
Oakland 0.18 0.19 in 1954 92 years
Mapleton 0.44 0.73 in 1967 75 years
Lake Mills 0.61 0.91 in 1988 58 years
Severe Weather. The dry weather resulted in relatively few severe weather events. The only widespread severe weather episode was on the evening of the 25th when high winds and/or large hail was reported from 34 counties.
Harry J. Hillaker, State Climatologist
Iowa Dept. of Agriculture & Land Stewardship
Wallace State Office Bldg., Des Moines, IA 50319
Telephone: (515) 281-8981, E-mail: Harry.Hillaker@IowaAgriculture.gov