UPDATE 1-Snowstorm slams road, air travel in U.S. Midwest
* More than 1,000 flights canceled in and out of Chicago
* Snow and ice make driving difficult in several states
(Adds details on crash in Wisconsin, storm forecasts)
MINNEAPOLIS, March 5 (Reuters) - A late winter storm dumped heavy snow on the midwestern United States on Tuesday, contributing to numerous highway crashes and flight cancellations as it moved east toward the Ohio Valley and the mid-Atlantic states.
More than 1,000 flights were cut in and out of Chicago's O'Hare and Midway airports and 107 more were cancelled in and out of Minneapolis-St.Paul International Airport, according to the FlightAware.com flight tracking service.
In western Wisconsin, a semi-tractor flipped off an Interstate 94 bridge and fully submerged in the Red Cedar River in Menomonie early Tuesday, said Christine Ouellete, a Wisconsin Transportation Department spokeswoman.
The truck's two occupants have not been heard from since the crash and rescue crews pulled the tractor from the river and were working to get into the cab, said Lieutenant Jeff Lorentz of the Wisconsin State Patrol.
The truck had been headed west, but the eastbound lanes of I-94 have been closed at the site since just after the crash for the rescue crews. The interstate was open otherwise.
Slick roads contributed to numerous crashes and a slow commute across the border in Minnesota. Driving conditions remained difficult along highways in parts of North Dakota.
Roads in northwest Illinois had patches of ice and snow on Tuesday and road crews were bracing in northeast Illinois for the storm, which began dropping snow on Chicago near the middle of the morning rush hour.
Chicago was forecast to get 4 to 8 inches (10 to 20 cm) of snow, down about 2 inches from a previous forecast, according to the National Weather Service. The heaviest snow was expected Tuesday afternoon in the region, up to 1 inch per hour, and expected to snarl the evening rush hour.
The storm was expected to move eastward over the Ohio Valley and then the central Appalachians and mid-Atlantic states on Wednesday, hitting Washington with its biggest snowfall in possibly two years, the National Weather Service said.
Winter storm warnings were in effect for all or parts of 16 states from the Upper Midwest to the mid-Atlantic on Tuesday, National Weather Service spokesman Chris Vaccaro said.
The storm was forecast to move across Ohio and the Tennessee Valley and merge with a developing storm off the mid-Atlantic states that could produce heavy, wet snow overnight and through Wednesday into the mid-Atlantic states that could bring down trees and power lines, Vaccaro said.
"It will be a wet, heavy, gloppy snow consistent with wallpaper paste," he said.
Vaccaro said upwards of 10 to 12 inches of snow was possible, and locally higher amounts in the Appalachians, West Virginia and eastern Maryland.
"We're expecting a sizeable accumulation for Washington DC, where there has not been a storm to produce more than 2 inches of snow since January 2011," Vaccaro said.
North Dakota on Tuesday was digging out from the storm, which caused blowing snow and drifts up to 3 feet (0.9 meter) high in blizzard conditions in the northwest oil region, a foot of snow near Minot and 15 inches near Grand Forks on Monday.
The North Dakota Transportation Department had lifted a no travel advisory on most roads by Tuesday morning.
In a separate storm, heavy snow and high winds were blamed for two major traffic accidents in the Colorado mountains, near the ski resort of Vail, involving more than 50 vehicles.
Three people were hospitalized from a 25-vehicle chain- reaction crash that closed a stretch of Interstate 70, the Summit County Sheriff's Office said in a statement. "None of the injuries were reported to be serious," the statement said.
A second pile-up about 17 miles (27 km) away on the same interstate involved 29 vehicles, with no reported injuries, the sheriff's office said.
(Reporting by David Bailey in Minneapolis, Jane Sutton in Miami, Ian Simpson in Washington, Keith Coffman in Denver and Dan Whitcomb in Los Angeles; Editing by Doina Chiacu and Andrew Hay)