The Ottumwa Courier

September 3, 2013

Could last week's heat mean cool end to month?

Courier staff writer

---- — OTTUMWA — The U.S. Department of Agriculture reported Tuesday that last week's heat took a bite out of Iowa's crop conditions.

Some heat is needed for crops to mature, the report said, but the heat also dried out soil that badly needs rain. Only 22 percent of the state's topsoil has enough moisture, a decline of six percentage points from last week.

Subsoil moisture fell even faster, by eight percentage points, to 26 percent adequate or surplus. Nearly three quarters of topsoil and subsoil is considered short or very short of moisture.

Most corn and soybeans remain in fair to good condition. But about a quarter of both crops is rated poor or very poor.

State Climatologist Harry Hillaker said temperatures averaged 11.7 degrees above normal across Iowa. The high temperature for the week was 104, and that was without the heat index.

Last week's heat wave was unusual, though not unprecedented. But there's reason to think it might be a prelude to unusually cool temperatures.

It sounds contradictory, but the National Weather Service in Des Moines says late summer heat has preceded cold weather by the end of September on a number of occasions. Saying one predicts the other is probably a step too far, but it's an interesting correlation.

In 1983, the NWS said, August hit high temperatures so regularly it drew comparisons to the Dust Bowl. The first week or so of September was hot as well, with highs in the upper 90s. By September 23 things changed and Des Moines saw the thermometer fall to 32 degrees. Mason City was even colder, at 22.

Other examples:

• A September heat wave brought triple-digit heat to Iowa in 1976. The town of Sibley hit 102 degrees on Sept. 6 and reached 99 the next day. Three days later the town had a low of 33 degrees.

• One of the hottest summers on record hit Iowa in 1939 and peaked in September. Temperatures ran over 100 degrees for several days. Light snow and sleet were reported by Sept. 30, with a statewide low of 16.

• September 1913 started hot, with temperatures of at least 90 degrees every day. On Sept. 5, Bedford hit 107 degrees. The morning of Sept. 22 was below freezing for much of the state, with a low of 19 degrees.

The record of wild September swings goes back to the 1800s. In 1895, temperatures hit 103 in mid-September, but a killing freeze struck less than two weeks later. Snow was falling by mid-September in 1881, but temperatures had been in the upper 90s at the end of August.