Why does it rain less in a drought? This fundamental question has an answer far more layered than one might expect. When a region of the Midwest and Great Plains has drought, there are usually fewer days with high humidity, and this contributes to less rainfall. However, the lower humidity is often a result of dry topsoil and so is more of a feedback of there having been less rain.
Summer drought usually has much more to do with upper level temperatures and wind speeds. During a summer drought, the jet stream spends more time than usual farther north, leaving the upper atmosphere above our region warmer and calmer. With upper level air warm, the rising air of afternoon thermals is less likely to cool enough to produce congested clouds. And with upper levels calm, the summertime dynamics make strong storms occur less frequently.