MADISON, Wis. -

About half of Wisconsin is considered in severe drought, according to a national group that studies ground moisture conditions.

Data released Thursday in the U.S. Drought Monitor’s weekly update shows 51.29 percent of the state is in of severe drought, an increase of more than 15 percent over the previous week. It represents the highest overall drought area in the last year.

Nationally, nearly two-thirds of the lower 48 states remain mired in some form of drought during the seven-day period ending Tuesday. The information comes as the corn harvest is in the homestretch in Midwest farming states where the nation's worst drought in decades is now clouding the prospects for the winter wheat crop.

According to the Drought Monitor’s heat map, the northeast part of the state is the least affected area and the counties on the Illinois border of the state in most affected.

More than 99 percent of the state is in some degree of drought. A year ago, 58 percent of the state was considered drought free.

Conditions in Iowa, the nation's biggest corn producer, remain unchanged, with three-fourths of the state still in the extreme or exceptional drought -- the two worst classifications.

The U.S. Department of Agriculture says 69 percent of the nation's corn crop has been brought in from the fields. That's more than double the average rate of the previous five years.

The U.S. Drought Monitor map is jointly produced by the National Drought Mitigation Center at the University of Nebraska-Lincoln, the National Oceanic and Atmospheric Administration, the U.S. Department of Agriculture, and about 350 drought observers across the country.