The map involves a combination of objective measurements like rainfall and soil moisture and subjective assessments, like the impact on crops.
“Drought is really defined by its impact,” Svoboda said. And, in the case of rain, it's possible for those impacts to appear weeks after the event.
Southeast Iowa remained unchanged. Most of the region is in severe drought. Most of Appanoose County is a step lower, in moderate drought, but that's the only county in the area that finds itself primarily in a different category.
But what does severe drought mean? Svoboda said the categories relate to the probabilities of equivalent conditions occurring in a given year. Severe drought (category D2) indicates conditions in the 10th percentile. So these conditions would be expected to happen an average of one year in 10.
Svoboda compared the measure to the idea of a 100-year or 1,000-year flood. It's not a precise comparison, but it is one people tend to be more familiar with.
“This would be equivalent to a one-in-10-year dryness,” he said.
There is a good chance for rain in the forecast. The National Weather Service expects a 70 percent chance of rain for the Ottumwa area on Saturday. Totals could be up to a half-inch, not nearly enough to make up the area's nearly 3-inch deficit for the month.
But given that it was more than a month between the last two significant rainfalls in Ottumwa, it's not something the area is in position to spurn, either.