Thursday, August 1, 2019

After a Soggy Spring and Early Summer, Drought May be Creeping Back

After a wet spring and early summer in much of the central and eastern U.S., dryness has become more established in the past three weeks especially in the central U.S. At the same time, drought conditions in the southeast U.S. have diminished in the past two months.

The maps of percent of normal precipitation for the U.S. the sharp contrast in precipitation between the period of May 1 through June 25, and from June 26 through the end of July.

The U.S. Drought Monitor released today is showing some expansion of D0 (Abnormal Dryness) across the central U.S. compared to a month ago, especially across the corn and soybean belt. Corn and soybean planting was delayed several weeks in some areas because of heavy rain and the resulting saturated ground and flooding. The dryness is spreading just as the corn is starting to pollinate in many areas, about two to three weeks later than normal.

The U.S. Drought Monitor for July 30 (l) and June 25 (r)

The rapid transition from wet to dry conditions is dramatically seen in the CoCoRaHS Condition Monitoring Report maps especially in the Midwest. The first map below is the condition map as of today, and the second map shows the conditions as of June 24. Note the moderate to severely wet conditions from Iowa through Illinois, parts of Missouri, and into Ohio as of June 24. In five weeks most of those have changed to normal to moderately dry.

CoCoRaHS Condition Monitoring report maps for the week ending August 1 (top) and ending the week of June 24 (bottom)

This may be the makings of a flash drought from Iowa though central Illinois into Ohio, as well as Michigan. A flash drought is characterized by a relatively short period of warmer temperatures and rapidly decreasing soil moisture. The "flash" refers to the rapid onset of drought, not the duration. In parts of the Midwest almost a month's worth of rain fell in the first week of July, but little since then. The last three weeks of the month were also extremely warm with highs in the 90s and 100s. At the same time, rain became scarce.

For example, at my location in east-central Illinois, I received more than 4 inches of rain the first week of July, close to normal for the entire month. During the last 24 days of the month I received only 0.22 inch. The ground went from being saturated to rock hard with cracks forming by the end of the month.

This is where CoCoRaHS condition monitoring reports can be very helpful. While July precipitation was near normal in my case, it doesn't tell the whole story because the rain largely occurred in a few days. Condition monitoring reports submitted weekly help those monitoring drought and environmental conditions to discern the current state and the impacts of too much or not enough precipitation.


  1. The word "normal" shouldn't be used when describing the weather. Average is a more appropriate term and it does matter what we say and how we say it. Our normal weather is drought to deluge. Numbers should be stated as averages.

    1. Larry, climate "normals" in this case refers to the average calculated for the 30-year climate period, as opposed to an average calculated, say, for 10 years or 20 years. It's a standard climatological term to refer to the calculations for these 30-year climate periods (long term), as opposed to weather (short term).

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