ST. LOUIS — Superstorm Sandy provided little relief to key Midwest farming states vexed by the stubborn drought that climate experts suggested Thursday could press on for months, complicating winter wheat crops and next spring’s corn and soybean plantings in the moisture-starved soil.

The weekly U.S. Drought Monitor update released Thursday showed that 60 percent of the land in the lower 48 states still was experiencing some degree of drought as of Tuesday. That’s down nearly 2 percentage points from a week earlier, taking into account much of the fallout from the massive storm Sandy, which dumped more than eight inches of rain on parts of the Eastern seaboard.

Roughly one-fifth of the land in the contiguous U.S. remained in extreme or exceptional drought, the two worst classifications, according to the latest update, which is put out by the National Drought Mitigation Center at the University of Nebraska in Lincoln.

Dry conditions continued weakening a bit in some Corn Belt states, although far too late to help this year’s withered corn and soybean crops. Farmers have nearly finished harvesting both crops, according to the U.S. Department of Agriculture, and yields were well below what was expected last spring when farmers planted a record amount of acreage with the crops.

Iowa, the nation’s top corn producer, saw one of the most-dramatic improvements, with half of that state still mired in the two worst categories of drought — a 13-percent upgrade from a week earlier.

The area of North Dakota gripped by some form of drought dropped 5 percentage points, to 90 percent, while Illinois saw that number slide by 18 percentage points, to 42.25 percent. Neither of those states now has any land in the two worst drought classifications.

Midwest farmers have turned their attention to their winter wheat crop, with little cooperation from the weather as about two-thirds of those plantings have taken place in drought-affected areas.

Kansas, the nation’s top grower of the grain, isn’t catching a break. Roughly 78 percent of the state is in extreme or exceptional drought, which is the same as the previous week.

That grim standing comes as 88 percent of the nation’s winter wheat crop has been planted, which is 3 percentage points ahead of the average over the previous five years. Sixty-three percent of the latest crop has emerged, down modestly from the pace of 67 percent during the past half-decade.

Forty-one percent of the U.S. winter wheat plantings are considered good, and an identical amount is deemed fair. Thirty percent of the crop is classified as poor or very poor.

Conditions of U.S. pastures and ranges appear to be on the upswing, with 40 percent of them labeled as poor or very poor — a 14 percentage point upgrade from last week. The 56 percent of grazing areas deemed fair or good is up from 44 percent the previous week.

With some rainfall expected in coming days from the southern Plains to the Great Lakes and the Northeast, climate watchers aren’t anticipating meaningful precipitation that would appreciably relax the grip of drought that has put soil moisture and levels of rivers and reservoirs used for irrigation at such a deficit.

Farmers embrace snowfall as a means of recharging soil moisture in time for each spring’s corn and soybean sowings, with about 20 inches of snow equating to just an inch of actual water, said Brian Fuchs, a National Drought Mitigation Center climatologist. But in many areas, he said, this year’s rainfall is 10 inches or more below normal — a big hole to dig out of.

“Winter is a fairly dry time of year for us anyway,” he said. “In the drought world, you typically don’t make up a lot of ground in the winter months.”

According to the National Oceanic and Atmospheric Administration’s latest seasonal outlook released Thursday, drought conditions are expected to persist from the Dakotas to Kansas and westward to California through January.

“I don’t see any large changes based on that in the next couple of months,” said Mike Brewer, a National Climatic Data Center scientist who authored the latest Drought Monitor update. “It could get tight leading into the next growing season.”