Heavy rains in the U.S. Delta and southeast over the next week will provide some relief from the worst drought in over 50 years while a cold snap early next week is posing a threat to the struggling wheat crop in the U.S. Plains States, an agricultural meteorologist said on Wednesday.

"That is something that definitely will need to be watched," said Andy Karst, meteorologist for World Weather Inc. referring to a turn to bitter cold weather early next week.

Karst said warmer weather this week would melt much of the insulating snowcover in the Plains, leaving the crop vulnerable to harm from extremely cold temperatures.

"It will be coldest Sunday through Tuesday and the biggest threat is in western Kansas, eastern Colorado and western Nebraska," he said. Temperatures are expected to fall to zero (degrees Fahrenheit) and below, Karst said.

Some of the soft red winter wheat crop in he U.S. southeast is being threatened by expected heavy rainfall and flooding, Karst said.

"There will be heavy rains in the Delta leaving from 5.00 to 7.00 inches by the end of next week. This will help boost soil moisture but also cause flooding, the biggest threat is to some of the soft red winter wheat crop," he said.

Commodity Weather Group (CWG) on Wednesday said rains favored much of central and eastern Texas, eastern Oklahoma and the southern Delta on Tuesday, and the weather models have continued to shift further south in the next day or so for the Plains.

"Notable rains are likely to remain focused on the southeastern quarter of the Plains, while Midwest and Delta soft wheat areas will see widespread coverage from this event," said CWG meteorologist Joel Widenor.

The weekly U.S. drought monitor report from last week showed snowfull in parts of the U.S. Plains had little impact on the historic drought gripping the region, but parts of Illinois, Wisconsin and the Southeast showed slight improvement.

The report issued last Thursday said 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.

The consortium of federal and state climatology experts are expected to issue a new drought report late this week. (Reporting By Sam Nelson; Editing by Theodore d'Afflisio)