Drought conditions in the United States grew even worse over the last week as historic drought conditions crept north and threatened new winter wheat planting in several states.

September was the driest in 118 years of U.S. record keeping for North Dakota, South Dakota and Montana and was the third-driest September for Nebraska and Oregon, said Mark Svoboda, a climatologist with the University of Nebraska's National Drought Mitigation Center.

"We had a brutally dry September. There is a lot of concern now about no moisture," Svoboda said. "A lot of folks are holding off and wondering if they should even plant winter wheat and plant spring wheat instead."

Fully 69% of the U.S. winter-wheat area is suffering from some level of drought, Svoboda said.

Roughly 63.5% of the contiguous U.S. was under at least "moderate" drought as of October 9, down from 64.6% a week earlier, according to the Drought Monitor, a weekly compilation of data gathered by federal and academic scientists issued Thursday.

But the portion of the United States under "exceptional" drought — the most dire classification — rose to 6.18%, up from 6.07% a week earlier.

In the High Plains, which includes Nebraska and the Dakotas, severe or worse drought levels covered 87.6% of the region, up from 87.5% the prior week. An estimated 28.2% of the region was in the worst level of drought, up from 28% a week earlier.

In Kansas, a top wheat growing state, drought levels improved slightly over the last week. "Extreme" drought, the second-worst level of drought, expanded to 95.7% of the state, up from 93.2% a week ago, though the worst level of drought was at 44.6%, down from 44.73%.