(Reuters) - Drought continued to expand through the central United States even as winter weather sets in, wreaking havoc on the nation's new wheat crop and on movement of key commodities as major shipping waterways grow shallow.
Unseasonably warm conditions have exacerbated the harm caused by the lack of needed rainfall. The average temperature for the contiguous United States last month was 44.1 degrees Fahrenheit, 2.1 degrees above the 20th century average, and tying 2004 as the 20th warmest November on record, according to the National Oceanic and Atmospheric Administration.
The year-to-date marks the warmest first 11 months of any year on record for the contiguous United States, and for the entire year, 2012 will most likely surpass the current record as the warmest year for the nation, NOAA said.
The warm weather accelerates evaporation of any precipitation that does fall, and keeps plants - like the new wheat crop - trying to grow, rather than slipping into normal winter dormancy.
"We have not seen hardly any rain or snow around the Plains states. It is still very dry. And with these temperatures when you are having 60- or 70 degrees and high winds... it's going to be problematic," said Brian Fuchs, climatologist with the National Drought Mitigation Center at the University of Nebraska-Lincoln.
Areas of drought expansion last week were noted across parts of Texas, central Louisiana, east-central Missouri, eastern Kansas, and the Panhandles of Texas and Oklahoma, according to the Drought Monitor's weekly compilation of data gathered by federal and academic scientists and issued each Thursday.
The U.S. High Plains, which includes key farm states of Nebraska, South Dakota, and Kansas, are the hardest hit. In that region, 58.39 percent of the land area is in extreme or exceptional drought, the two worst categories of drought. A week ago, the tally was 57.89 percent.
Nebraska remained by far the most parched state in the nation with fully 100 percent of the farm state in severe or worse drought, and 77.46 percent of the state considered in "exceptional" drought - the worst level, according to the Drought Monitor.
Overall, roughly 62.37 percent of the contiguous United States was in at least "moderate" drought as of December 4, a slight improvement from 62.55 percent a week earlier,
The portion of the contiguous United States under "extreme" or "exceptional" drought expanded, however, to 20.63 percent from 20.12 percent.
Roughly 65 percent of the new winter wheat crop is in drought-hit areas, according to the U.S. Department of Agriculture and many producers might elect to abandon the crop due to its extremely poor condition, the government said.
Since the 1950s, there have been only two years when U.S. winter wheat abandonment reached or exceeded one-quarter of the crop - the 1988-89 season and the 2001-02 season. Current U.S. winter wheat conditions are worse now than in November of those seasons, USDA said.
Worries about the wheat crop come alongside worries about movement of already harvested crops and other commodities down the Mississippi River, a critical waterway for shipping goods from the central states.
Water levels are forecast to drop to near-historic lows by mid-December on the "middle river" of the Mississippi- the stretch from St Louis to Cairo, Illinois. More than 100 million tons of cargo, half of it corn and soybeans, float through that stretch of river annually.
Some relief may be in sight, according to Brad Rippey, USDA meteorologist. Portions of the northern and central Plains and upper Midwest should see snow from December 8-10, he said.
(Reporting by Carey Gillam in Kansas City; Editing by Bob Burgdorfer)