* Snow in U.S. Plains has no impact on drought condition
* Drought expected to persist in Plains in next three months
* Precipitation in U.S. Midwest brings modest drought relief
CHICAGO, Jan 3 (Reuters) - Snowfall in parts of the U.S. Plains last week had little impact on historic drought gripping the region, but parts of northern Illinois and southern Wisconsin showed slight improvement, weather experts said.
A weekly report issued Thursday by a consortium of federal and state climatology experts said that as of Jan. 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 was insufficient and did not offer much drought relief, according to the weekly U.S. Drought Monitor report.
"Precipitation in Oklahoma had little impact on reservoir and lake levels, and agricultural reports indicated that soil moisture remained depleted and the condition of small grains and canola across the state continued to deteriorate," the report 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 Dec. 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 and zero percent excellent, compared with 74 percent a year earlier for those categories combined.
In a seasonal outlook released Thursday, the U.S. Climate Prediction Center said extreme to exceptional drought was likely to persist across the Plains for the next three months.
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 and southern Wisconsin.
The Drought Monitor showed that 8.9 percent of Illinois was in severe drought as of Jan. 1, a drop from 9.29 percent the previous week and down from more than 31 percent three months ago.
In its three-month outlook, the Climate Prediction Center said continued drought improvement is possible across the Midwest and in northern tier states including Minnesota, North Dakota and Montana.
Illinois is the No. 2 U.S. producer of corn and soybeans, and farmers in the Midwest are monitoring soil moisture conditions ahead of spring planting. USDA said that as of Dec. 30, subsoil moisture was short to very short in two-thirds of the state.
As a result of drought, water levels on the Mississippi River are approaching historic lows, impeding the transit of grain-bearing barges from the Corn Belt to the U.S. Gulf Coast export terminal.