* Snow in U.S. Plains has no impact on drought condition
* Drought expected to persist in Plains next three months
* U.S. Midwest, South sees modest drought relief
* Low water on Mississippi River remains a worry
By Julie Ingwersen
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 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 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 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 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 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 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.
However, concerns persist about historically low water levels that may halt shipping on part of the Mississippi River, a key artery for barges carrying grain from the Corn Belt to the U.S. Gulf Coast.
The snowpack in the Rocky Mountains, which eventually helps supply moisture for the Mississippi, is below normal, said Mark Svoboda, a climatologist with the University of Nebraska's National Drought Mitigation Center.
"They get most of that snow typically later in the winter. But they are still running 20 to 30 percent below normal," Svoboda said. "That does not bode well for the Missouri Basin, the Platte, the Arkansas - those feeders into the Mississippi basin," he said.
RAINS AMELIORATE DROUGHT IN SOUTH
Drought conditions eased in the South after storms brought two to four inches of rain from eastern Texas to the Carolinas, the Drought Monitor report said. In Alabama, about one-third of the state remained in moderate to extreme drought but the rain eliminated the "exceptional" drought category that had covered about 3.7 percent of the state a week earlier.
However, the report cautioned that long-term moisture deficits persisted in the region, and dry weather continued across much of western, central, and southern Texas.