Preliminary statistics show Iowa has just experienced its coolest July on record.

"Time will tell if that's good or bad," said State Climatologist Harry Hillaker. "It means better air-conditioning bills than usual. About 35 percent less air-conditioning requirement as a normal July."

"For the most part it's been good for the crops," Hillaker said of the remarkably low July readings. "The good news is that corn and beans were planted on time, except for extreme southern Iowa. So most of the state will have a full planting season."

It's a bit counter-intuitive, but Hillaker said some of the best crop yields have occurred in cool summers
, like 1992, 2004 and 2008.

Cool temperatures also slowed mosquito development, according to Lyric Bartholomay, assistant entomology professor at Iowa State University.

Mosquitoes like to speed through the larvae and pupae stages in toasty warm water. Cooler water extends the process. So, fewer bites in recent weeks.

Here's how the state record stacks up at this point. The current statistic for lowest July temperatures was set in 1891 with highs and lows averaging 68.3 degrees.

The average for July 2009 as of Friday morning was 68.1 degrees and Hillaker said temperatures were cool enough across the state that Friday's readings wouldn't change it.

But there is an asterisk. "The numbers I have are based on 75.5 percent of the official temperature sites in Iowa," Hillaker said. "We don't have the other 24.5 percent yet. Some of them will be coming in through the mail. That could mess up the averages, but I don't think it will change it much."

Iowa was off to another cool start on Friday morning with many spots in the state starting off in the low 50s.

How cool was it in northern Iowa last month? The warmest overnight temperature in Algona and Sheldon in July 2009 was 61 degrees.

"The key was how persistent it's been," said Hillaker. "We usually get some hot, humid air and some really warm overnight temperatures. We didn't have anything even approaching that this July."

The low July temperature in Iowa this year was 42 degrees at Sibley, Sheldon and Spencer on the 19th, and at Elkader on the 20th.

The record low temperature in Iowa in July is 35 degrees, set at three sites over the years, most recently at Elkader on July 7, 1984.

The impact on livestock is generally very, very, good," said Hillaker. "But it backfired on us in June, especially in southwest Iowa. A lot of cattle died in a very short heat wave. June had been cool, too, until about June 17."

Coolest average temperatures for July in Iowa

2009: 68.1 degrees *
1891: 68.3
1992 68.7 degrees
1882 68.9 degrees
1915 69.3 degrees

Source: Office of the state climatologist