The latest U.S. drought map shows that excessively parched conditions continue to worsen in the Plains states that are key producers of corn and soybean crops.

The weekly U.S. Drought Monitor map released Thursday shows that the amount of the contiguous U.S. mired in drought conditions dropped a little more than 1%age point, to 78.14%. But the expanse still gripped by extreme or exceptional drought rose nearly 2%age points to 24.14%.

That's because key farm states didn't get as much benefit from rains as elsewhere.

The nation's biggest corn and soybean producer, Iowa, is still grappling with the drought. The amount of that state in extreme or exceptional drought more than doubled, rising from 30.74% last week to 69.14% as of Tuesday.