Updated

Hurricane Isaac's remnants dumped heavy rain on some key Midwest farming states, dramatically lessening the drought there while corn-producing heavyweights Iowa and Nebraska missed out on that moisture and saw their conditions worsen badly, according to a drought report released Thursday.

The U.S. Drought Monitor's weekly report came as federal forecasters separately warned that the worst drought in decades could persist for months in a large swath of the central and southern Plains, portions of the Rockies and much of California.

"Most of these areas are moving toward a climatologically drier time of year, and there is no compelling indication that substantially above-normal precipitation will fall during the next three months," according to the National Weather Service's Seasonal Drought Outlook.

That would be bad news for Nebraska, which paid an especially high price for losing out on Isaac's rainfall as the storm moved northward through the central U.S. The area of that state deemed to be in exceptional drought — the highest classification — ballooned 47 percent, to 71 percent, in the seven-day period ending Tuesday, the latest Drought Monitor update showed.

In Iowa, the nation's biggest corn producer, the area of land deemed to be in exceptional or extreme drought rose 4 percentage points, to 62 percent.

When it comes to states getting moisture during this worst drought in two generations, "it's just like it's been all summer — there are the haves and the have-nots," said Brian Fuchs, a National Drought Mitigation Center climatologist who authored Thursday's update.

Even in states that got rain from Isaac — in some cases as much as 10 inches — the relief came far too late in the growing season to offer much help to withered corn crops, which already are being harvested. But there was reason to cheer, as other crops such as soybeans still are maturing.

Southeast of St. Louis near Coulterville, Ill., Dean Campbell concedes "Isaac blessed us with some water," by some accounts several inches. But that won't save his 900-acre corn crop bound for being a bust. With about 40 percent of his harvest done, Campbell says he's averaging a "very, very poor" 14 bushels per acre — a snippet of the 130 bushels he's normally get.

"We're not anticipating a bumper crop by any means," said Campbell, 60, who was more optimistic about his still-maturing 1,100 acres of soybeans, which can still make use of the rain. He won't know what that outcome will be until reaping that crop several weeks from now.

"We have potential in the bean field," he said. "We won't have a record crop, but we'll have a reasonable crop. That's the typical response from anyone in the Midwest."

Missouri, which in some places got as much as 6 inches of rainfall from Isaac, saw the area of land in exceptional drought plummet from 35 percent last week, to just 3 percent of the state. The area in extreme or exceptional drought plunged a whopping 66 percentage points, to 32 percent of the state.

In neighboring Illinois, the extent of the two worst classifications of drought spiraled from roughly 70 percent to about 7 percent, with Isaac's rainfall erasing the exceptional drought that had gripped nearly 8 percent of the state. None of Indiana is now in exceptional or extreme drought, when 39 percent of the state was deemed as such the week before.

More than 10 inches of rain fell in parts of Arkansas, which sat squarely in Isaac's path, helping cut the amount of state in exceptional drought to 12 percent, down 33 percentage points from a week ago. Half of the state still remains in extreme drought.

Overall in lower 48 states, the area deemed to be in extreme or exceptional drought dipped only roughly 2 percentage points, to just over 21 percent.

As of last Sunday, during a weekend in which Isaac was creeping across middle America, more than half of the U.S. corn crop — 52 percent — remained in poor or very shape, unchanged from a week earlier, according to the USDA's weekly crop update released Tuesday.

Growers are getting their first true look at the extent of the damage as they already are bringing in their corn crops, weeks ahead of schedule because of an earlier planting season this year.

The USDA said Tennessee has harvested roughly half of its corn, when in a normal year it would have harvested 21 percent of its crop by this time. Missouri is at 44 percent, ahead of the average 8 percent. Nebraska is at 7 percent while Iowa, the nation's leading corn producer, is at 5 percent.

While much of the nation's corn crop was punished by the drought, soybeans have proven more resilient to the withering summer, partly because bean plants are not as far along in their growing season and still can benefit from moisture and produce pods.

Some 37 percent of the nation's soybean crop was classified in poor or very poor condition, down 1 percent from a week earlier, the USDA said. But some Plains states that got the brunt of Isaac benefited more than those that got little from it; in Illinois, where the statewide rainfall averaged more than 3 inches, 40 percent of the state's soybean crop is considered poor or very poor, an 11-percent improvement from the previous week.