Cool, wet late winter weather across most of the U.S. Corn Belt has raised hopes that the world's largest food exporter will rebound from last year's historic drought but experts warn that many crop and pasture areas west of the Mississippi River remain bone dry.

A series of storms in the past month brought several feet of snow and much needed moisture to the central United States, replenishing parched soils and filling low rivers just as the U.S. planting season nears. Moisture is near normal for farms east of the Mississippi River, the dividing line of the western and eastern Corn Belt. But the west has not been as fortunate.

The weekly U.S. Drought Monitor, which last summer rated two-thirds of the U.S. land mass in "moderate to exceptional" drought, on Thursday showed drought areas shrank since December. But 51 percent of the country was still rated as having moderate drought conditions or worse as of March 19.

"We've certainly made a significant improvement to the agricultural drought over portions of the Midwest, particularly the Corn Belt - Iowa, Illinois, Indiana, Missouri and even portions of eastern Kansas and Nebraska," said Mike Hudson, a meteorologist with the National Weather Service.

"But the long-term drought is still hanging on very strongly over portions of western Kansas and western parts of the wheat belt up to the Dakotas and Nebraska," he added.

The United States for decades has been the largest exporter of wheat, corn and soybeans, with most of those crops grown in the Midwest and central Plains. Last year's drought was the worst in more than 50 years and cut into the role of the United States as the world's breadbasket, with Brazil now seen as the top soybean exporter.

Ground zero for crop watchers is now the fourth largest U.S. corn state, Nebraska, which is also a leading producer of cattle, wheat, sorghum (milo) and ethanol. More than half the state depends on irrigation to support its corn crop. Even with irrigators running around the clock last summer, corn output dropped 16 percent compared to the previous year.

"We are in much worse shape right now than we were this time last year. It's going to take an incredibly wet period for the next couple months for us to have a chance to escape the type of damage we incurred last year because we have less soil moisture to start off with," Al Dutcher, Nebraska state climatologist, said in an interview.

"Even with normal precipitation we could see impacts as aggressive as last year because there just isn't any available moisture," he added. "We are hitting a critical time."

This weekend another storm is expected to move through the center of the country, dumping up to a foot of snow in a stretch from Kansas to southern Indiana. Melted precipitation would be one-quarter to one-half inch of moisture, amounts far below what is needed to replenish soils, climatologists say. 

Nebraska monitors soil moisture at 50 stations across the state. Late winter storms provided enough precipitation to help soil moisture 12 inches deep in east central and south east Nebraska, Dutcher said, but soils remain rock hard two feet below the surface.

"As you move north and west of this area most locations have less than an inch of available moisture," Dutcher said.

While 96 percent of Nebraska is still rated in extreme to exceptional drought, South Dakota and Kansas are under similar stress. Two-thirds of South Dakota and Kansas - major wheat, corn and cattle states - are in extreme to exceptional drought.

The most immediate impact of the continued dryness is on pastures for cattle to graze and on the hard red winter wheat crop - the main U.S. bread wheat -- as it comes out of dormancy.

Kansas has had 70 percent of normal precipitation since September, which comes on the heels of last summer's drought.

"What you are seeing is mainly surface improvement, but it's not enough to sustain even the wheat crop for its final maturity and certainly not enough to do anything for the spring crops like corn or soybeans or milo. We'll take it but we've got a lot more improvement to go," said Kansas climatologist Mary Knapp.

Iowa, the top U.S. grain state, has seen moisture but its northwest corner remains rated in severe to extreme drought.

West versus East 

Unlike the western Corn Belt, soil moisture east of Mississippi River has largely recovered.

"For Illinois we are in really good shape right now thanks to late season winter storms that brought us a little extra moisture, either snow or rain," said Jim Angel, the state climatologist for Illinois, the second biggest grain state.

"The state as a whole is two or more inches above average for this year through this date. We were about two to three inches below average last year. It's a night-and-day difference between the two winter time experiences."

"he only thing we can say with some degree of certainty is we're going to have a slower start to the growing season," Angel said, citing current cold soil temperatures. 

So Nebraska remains the focus of 2013 drought fears.

The state would need to see 150 percent of normal rain over the next six weeks, equating to six to seven inches of rainfall in the east and four to five inches in the west, Nebraska climatologist Dutcher said.

"The precipitation events that have occurred recently are encouraging. Unfortunately the impacts of the 2012 drought year pulled all moisture out of the profile. So the only moisture we have going for us is right at the surface," Dutcher said.

Dutcher added that he was also concerned about snowpack in the Rocky Mountains, which may reduce river-based irrigation.

"Perfectly timed rainfall in an aggressive pattern for the next six weeks can bring us back up to where we feel comfortable that we would have a decent chance of hitting average yields," he said.