Ag Weather Forum

Late-August Dry Details

Bryce Anderson
By  Bryce Anderson , Ag Meteorologist Emeritus
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Much of the Midwest is in some level of drought at the end of August, including extreme drought in west-central Iowa. (U.S. Drought Monitor graphic)

A very hot final full week of August has left its mark on Midwest crops. The high-production corridor of the region between Interstate 70 on the south and Interstate 90 on the north experienced temperatures that were from 6 to 12 degrees Fahrenheit above normal; most of this swath saw temperatures that were 8 to 12 degrees F above normal. That difference was evident at all hours of the day or night -- the heat never let up. And, crop conditions and yield prospects are showing that withering impact.

Of course, a lot of attention has been paid to the flash drought in Iowa, and with good reason. Iowa state agriculture department climatologist Justin Glisan noted in the state crop report on Aug. 24 that the state was the driest since 2013 when the entire state had some phase of drought in effect per the Drought Monitor.

However, one could make the case that in western Iowa conditions are worse than seven years ago, because a large group of 12 counties in west-central Iowa are in extreme drought (D3). For these counties, it's the worst drought since 2012.

The upcoming week offers some respite from the heat, but little meaningful rainfall in the driest areas. Temperatures are forecast to show a below-normal tendency. This would at least slow down the pace of drying. However, rainfall in the most moisture-deficient areas is unlikely to take a quick turn to suddenly wetter.

Meanwhile, the Pacific Ocean Southern Oscillation Index (SOI) reached La Nina readings during the past weekend. The 30-day SOI moving average Aug. 31, at plus 8.97, is in the La Nina category. (La Nina SOI values start at plus 8.0.) The general effect of La Nina is for below-normal precipitation in the central U.S. That adds a longer-term drier influence to this late-season pattern.

Bryce Anderson can be reached at

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