The heat, combined with sparse snow cover, set the stage for drier soils heading into the growing season. Drier soils also meant less evaporation to ease the warmth.
The drought began to spread in April, gathering intensity to strike in force in May, June, and July, Mr. Miskus says. Its timing couldn't have been worse. High temperatures that accompanied the growing drought came as corn and soybeans were set to pollinate.
"When temperatures reach above 95 degrees, corn doesn't pollinate," he says. "We haven't seen a drought like this hit that area since 1988."
The '88 drought triggered congressional hearings on global warming that significantly raised the issue's public profile.
To explain the current drought's persistence, meteorologists point to a dome of high pressure that has been doing a rumba back and forth across the country's midsection.
Storms moving in off the Pacific have moved up over the dome into southern Canada before moving back down the eastern side of the dome to moisten the East Coast.
Given the history of drought in North America – including three decade-long droughts in the 1800s and one in the 12th century that lasted 40 years – it's difficult to spot changing trends that would clearly point to human-triggered climate change as a significant factor, says Richard Seager, a climate researcher at the Lamont-Doherty Earth Observatory in Palisades, N.Y., who focuses his research on multiyear droughts.
"The climate system has a tremendous amount of noise in it," he says. "You're trying to detect an emerging human-induced signal amongst this colossal natural variability. It's very hard to do."