An early season snowstorm forced the closure of many roads, schools and offices in southeastern Wyoming and generated black ice in the Casper area on Thursday.

Doug McGee, public affairs officer for the Wyoming Department of Transportation, said 122 vehicle crashes had been reported statewide from Wednesday morning to Thursday morning. No fatalities were reported.

Transportation officials closed Interstate 80 in southeastern Wyoming and parts of Interstate 25 in the Cheyenne, Chugwater, Wheatland, Glendo and Douglas areas for much of Thursday.

"This is an extraordinarily intense storm for this early in the winter season," said Capt. Perry Jones of the Wyoming Highway Patrol. "I think people traveling through Wyoming in February expect it to be winter, but in October, it's not generally this bad."

Most of the crashes in southeastern Wyoming were minor, Jones said.

He said the biggest wreck occurred Wednesday morning, when 13 semitrailers and three passenger vehicles collided near the Harriman interchange on eastbound I-80 between Cheyenne and Laramie. Jones said two people were seriously injured, one of them suffering life-threatening injuries.

Another crash on I-80 between Cheyenne and Laramie on Wednesday morning also involved several semitrailers, but Jones said no one was seriously hurt.

Rebecca Mazur, a meteorologist and forecaster with the National Weather Service in Cheyenne, said the storm was expected to move off to the east by Thursday evening.

Blowing snow will continue to be a concern into today, Mazur said. She said drifts were running up to 4 feet in Cheyenne on Thursday and up to 6 feet 30 miles north of Cheyenne.

"The winds will be the main concern through the night," Mazur said.

The Cheyenne-Laramie County Health Department canceled the H1N1clinic -- swine flu immunization -- for pregnant women that was to be held from 1 p.m. to 4 p.m. today. The clinic will be rescheduled at a later date.

The storm began Tuesday evening, adding enough snow to break total snowfall records for October. More than 25 inches of snow had fallen in the region so far this month, compared with the previous record of 23.1 inches set in 1906, Mazur said.

"We do see these storm systems move through this time of year, but I do think the magnitude, the intensity of this storm system, is abnormal," Mazur said. "I don't think we normally see 1- to 2-foot snowfalls here on the plains in October."

Chris Boswell, chief of staff to Gov. Dave Freudenthal, said state offices opened two hours late on Thursday.

"Generally speaking, we're up and open for business, but certainly it's a challenge at this point," Boswell said.

Black ice advisories for major roads in Natrona County remained in effect Thursday evening. The advisories stretched from I-25 between Glenrock and Casper and on through to mile marker 210 at the interchange with Wyoming Highway 259 that leads to Midwest, according to the WYDOT Web site.

The advisories also included:

-- U.S. Highway 20/26 from Glenrock (the Old Glenrock Highway) through Casper to Waltman;

-- WYO 220 from Casper to Alcova;

-- and WYO 251 (Casper Mountain Road).

Black ice occurs when moisture on the road surface freezes, which causes extremely slick conditions that may not be seen by motorists.