General Summary. Iowa temperatures averaged 75.3º or 1.5º above normal while precipitation totaled 7.93 inches or 3.68 inches more than normal. This ranks as the 45th warmest and 5th wettest July among 138 years of records.
Temperatures. Hot weather was the rule for most of the month as below normal temperatures were confined to only seven days in July. However temperature extremes, thanks to high humidity and plentiful cloudiness, were subdued with a statewide range from only 53º to 98º. The lowest temperatures were recorded at Anamosa, Elkader, Lowden and Maquoketa on the 2nd and also at Sibley on the 8th, 15th and 21st. Ankeny was the hot spot on the 14th. The statewide minimum temperature of 53º is the highest July minimum since at least 1879. Only July 1993 has seen a smaller range in temperatures (50º to 94º). High humidity resulted in exceptionally high heat indices which officially reached as high as 115º at Ames on the 14th and 110º at Burlington on the 23rd.
Cooling Degree Day Totals. Home air conditioning requirements, as estimated by cooling degree day totals, averaged 173% greater than the record low July total of one year ago and 16% more than normal. Cooling degree day totals so far this year are running 92% greater than last year and 16% more than normal.
Precipitation. The first three days of July were dry but that was not a sign of things to come as precipitation was frequent and heavy for the remainder of the month. Although July rainfall was not as great as in June it was more concentrated in short periods of time which resulted in greater flooding. The largest rain event of the month came on the night of the 22nd when Oelwein officially recorded 9.93 inches of rain. An additional three to four inches of rain fell over the same areas of northeast Iowa the next night. The result was record flooding along the entirety of the Maquoketa River and the destruction of Lake Delhi. Monthly precipitation totals varied from 3.86 inches at Bedford to an exceptional 20.33 inches at Oelwein. The Oelwein total far exceeded their previous wettest month of 13.30 inches in June 1925 among 87 years of records. Major flooding also occurred in Appanoose County where Lake Rathbun Dam reported 6.89 inches of rain on the night of the 4th and another 5.80 inches on the night of the 19th on the way to a monthly total of 16.20 inches of rain. Greatest flooding occurred after the second rain event when the water level exceeded the spillway with the Rathbun lake level cresting on July 24 just 4.7 inches lower than the record set on July 28, 1993.
Outlook. Historically years with a transition from El Niño to La Niña conditions, such as 2010, have seen a strong tendency for above normal temperatures throughout the summer and through most of the fall in Iowa. Thus, the relatively hot and humid weather we have seen so far this summer is very likely to continue through August. However, El Niño to La Niña transition years are not good predictors of precipitation at this time of year in Iowa. The high soil moisture levels that we currently have probably will help maintain the wet weather pattern into August, but hopefully it will not be as excessively wet as the past two months.
Harry Hillaker, State Climatologist
Iowa Dept. of Agriculture & Land Stewardship
Wallace State Office Bldg.; Des Moines, IA 50319
Phone: (515) 281-8981 |
