ST. LOUIS (AP) — The nation's most withering drought in decades only got worse in several key farming states last week, despite cooler temperatures that at least gave those living there a break from this summer's stifling heat, according to a new drought report released Thursday.

In its weekly map, The U.S. Drought Monitor showed that as of Tuesday, just over two-thirds of Iowa, the nation's biggest corn producer, was in extreme or exceptional drought — the worst two classifications. That's up more than 5 percentage points, to 67.5 percent, from the previous week.

Nearly all of Nebraska, Kansas, Missouri and Illinois are in extreme or exceptional drought, with Illinois showing the most-dramatic climb in those categories, spiking 17 percentage points in one week, to 96.72 percent, according to the map. In neighboring Indiana, where 5 inches of rain fell in some parts, the area of the state in exceptional or extreme drought fell 9 percentage points, to 37.09 percent.

Conditions cooled in the region, but little or no meaningful rain fell, said Mike Brewer, a National Climatic Data Center scientist who put together the latest weekly U.S. Drought Monitor map released by the National Drought Mitigation Center at the University of Nebraska in Lincoln. The lack of rain allowed exceptional and extreme drought conditions to continue to expand in the area from northern Missouri and into Kansas and Nebraska, he said.

Plains farmers have begun harvesting what corn managed to survive this summer, although in some areas growers cut their fields weeks ago, chalking the year up as a loss. Many ranchers have sold livestock because they had no grass for grazing or money to buy feed, which has soared in cost.

In the lower 48 states, there was a slight increase in the overall area experiencing at least some drought, from 61.77 percent on last week's map to 63.2 percent on this week's. There was little change in the overall area experiencing exceptional or extreme drought, which went from 6.26 percent last week to 6.31 percent this week.

Rain is expected in the northern Plains in the next few days, although it may come too late to save the region's withered crops.

The U.S. Agriculture Department twice has slashed its forecast for this year's corn and soybean output because of the drought in the nation's breadbasket. It forecast the nation's biggest harvest ever in the spring, when farmers planted 96.4 million acres of corn — the most since 1937. But the agency has cut its estimate twice since then and now expects the nation to produce 10.8 billion bushels, the least since 2006.

If that estimate holds, the federal government says it will be enough to meet the world's needs and ensure there are no shortages. But experts say food prices will almost certainly climb as corn is a widely used ingredient in products ranging from cosmetics to cereal, colas and candy bars.