The latest U.S. Drought Monitor survey shows an increase in extreme drought conditions in four Plains states but a slight decrease in the overall area of the lower 48 states experiencing some form of drought.

The map posted Thursday on the monitor's website shows that nearly two-thirds of the lower 48 states is experiencing some drought. Recent rainfall pushed the percentage down to 62.91, from last week's 63.86.

The report says one-fifth of the U.S. is experiencing extreme drought. That number ticked up nearly 2%age points to 22.3%, largely because of worsening conditions in parts of Kansas, Missouri, Nebraska and Oklahoma.

The area of the lower 48 states classified as facing exceptional drought, the most serious classification, rose from 2.38% last week to roughly 3%.