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 3^rd 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 (10^th-11^th & 27^th-28^th) of the month.   Daily readings were more than ten degrees above normal on the 3^rd-6^th, 17^th-18^th and 23^rd-25^th.   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 23^rd.   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 11^th and 12^th.

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 25^th.   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 25^th 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