By Julie Ingwersen

CHICAGO (Reuters) - Snowfall in parts of the Plains last week had little impact on historic drought gripping the region, but parts of Illinois, Wisconsin and the Southeast showed slight improvement, weather experts said.

A weekly report issued Thursday by a consortium of federal and state climatology experts said that as of January 1, 42.05 percent of the contiguous United States was in severe to exceptional drought, down from 42.45 percent the previous week.

Parts of the central Plains received snow in the last week, providing some much-needed protection for the region's dormant winter wheat crop before temperatures plunged at the end of December.

However, the snow did not offer much drought relief, according to the weekly U.S. Drought Monitor report.

"It's getting colder now and the ground is starting to freeze up, so if any precipitation does fall, it's not going to go into the soil," said David Miskus, a meteorologist with the U.S. Climate Prediction Center who contributes to the Drought Monitor.

In a seasonal outlook released Thursday, the Climate Prediction Center said extreme to exceptional drought was likely to persist across the Plains for the next three months.

"Most of the annual rainfall for the High Plains really occurs in the springtime and early summer, so that is going to be the critical period. They really do need a wet season this year to make any kind of dent in the drought," Miskus said.

Earlier this week, the U.S. Department of Agriculture said that in Kansas, the top wheat producing state, 24 percent of the crop was rated in good to excellent condition as of December 30, a drop from 29 percent at the end of November. USDA attributed the decline to limited moisture.

In Nebraska, only 14 percent of the winter wheat crop was rated good while zero percent of it was rated excellent. That compared with 74 percent a year earlier for those categories combined.

Current drought conditions are most severe in Nebraska, where the Drought Monitor shows more than 77 percent of the state suffers from "exceptional" drought, the most extreme category.

SLIGHT IMPROVEMENT IN MIDWEST

Drought conditions in the Midwest showed incremental improvement in the last week, with recent storms bringing welcome moisture to northern Illinois, the No. 2 corn state, and southern Wisconsin.

The Drought Monitor showed that 8.9 percent of Illinois was in severe drought as of January 1, a drop from 9.29 percent the previous week and down from more than 31 percent three months ago. Continued...