Dozens of tornadoes and severe storms hammered the northern Plains and Midwest this weekend, with the governor of Nebraska declaring a state of emergency, officials said Sunday.

One person was killed as a tornado ripped through Hallam, Neb., a small town south of Lincoln, the Omaha World-Herald reported on its Web site Sunday, citing a Nebraska State Patrol spokeswoman.

More than 80 tornadoes were confirmed to have touched down in the region Saturday as a weather front stalled over the area. Unseasonably warm, humid air from the south collided with waves of low pressure on the front, said Oliver Lucia, meteorologist with Meteorlogix weather service.

"That's just perfect ingredients to set things off," Lucia said.

Nebraska Gov. Mike Johanns (R) declared a state of emergency Saturday, with many counties in the state confirming tornado touchdowns, said Terri Teuber, a spokeswoman for the governor. The declaration allows the governor to call up National Guard troops and gives the state access to emergency funds.

Johanns said Hallam, a town of about 275, suffered "near total devastation," and he was uncertain whether it could be rebuilt, the Omaha World-Herald reported after Johanns toured the damage.

"It just tore this town apart," he said.

Parts of Iowa and central Michigan were also hard hit, Lucia said, adding that more severe weather was expected late Sunday, especially in southern Michigan and Wisconsin, northern Illinois and Iowa and northwest Ohio. Storms could extend into New York and Pennsylvania, he said.

In Illinois, parts of Chicago suburbs Gurnee and Des Plaines were flooded as the Des Plaines River overflowed its banks. In Gurnee, the river was not expected to crest until Tuesday at 12.4 feet, more than five feet above flood stage, according to the National Weather Service.

Storms over the past several days, with large hail and flash floods, also killed at least three other people.

Three people were killed in Michigan's Berrien and St. Joseph counties Friday when trees fell on their cars in separate incidents, said Chris Corteville of the Berrien County Sheriff's Department.

A tornado Friday injured 15 people and destroyed nearly all the houses in Bradgate, Iowa, population 124, according to the Humboldt County Sheriff's Office.

Rainfall this spring has been above average from the middle of the Mississippi Valley through the Great Lakes and northern Midwest, Lucia said.