SPOKANE — An avalanche on Interstate 90 closed the westbound lanes at Snoqualmie Pass on Wednesday, just four hours after the pass opened after the longest weather closure since 2002.

The state Department of Transportation said eastbound traffic remained open Wednesday, but vehicles heading west were being stopped near Cle Elum, 28 miles east of the summit.

There was no immediate estimate on when the roadway would reopen. Officials had said earlier in the day that the freeway might have to be closed again Wednesday evening because of avalanche danger, with a major winter storm forecast to drop 2 feet of snow on the pass starting late in the day.

“If it snows as much as they are predicting, we might have to close it again to do avalanche work,” said Transportation Department spokeswoman Meagan McFadden.

The state’s main east-west route was closed about 7:30 a.m. Tuesday after a snow slide blocked the eastbound lanes. It remained closed for nearly 28 hours until one lane in each direction was reopened at 11 a.m. Wednesday.

That’s the longest since it was closed for 22 hours in 2002, McFadden said.

Throughout the day, cars and trucks crept across the 3,011-foot pass, about 50 miles east of Seattle, hindered by the snow and ice-covered roadway.

Before dawn Wednesday, workers detonated about 500 pounds of explosives to bring down more loose snow and plowed enough snow and debris to fill about 130,000 dump trucks, state Transportation Secretary Paula Hammond said.

Wet, heavy snow falling on a hard icy layer created treacherous conditions, Hammond said.

Traction tires and chains were required on the pass.

More than 200 trucks were backed up Tuesday at North Bend on the west side of the pass, which is traversed by 6,500 to 7,000 trucks on a typical weekday.

To the north, U.S. Highway 2 was reopened through Stevens Pass at 6 a.m. Wednesday following three hours of avalanche control work

South of I-90, U.S. 12 remained open through White Pass and State Route 14 was open through the Columbia River gorge.

In the southeast corner of the state, heavily traveled U.S. 195 was closed south of Pullman, home of Washington State University, to the Idaho border. Four state highways south of Spokane and west of Pullman also were closed because of blowing and drifting snow.

Schools in Spokane and much of Eastern Washington were closed for a third consecutive day Wednesday as the succession of storms covered roads with ice and snow and snarled traffic. The snow days in Spokane, which has one of the largest public school systems in the state with 30,000 students, were the first since 1996.

Spokane County has spent about $2 million on snow plowing in 2008, $500,000 more than was budgeted for the entire calendar year, county Engineer Robert F. Brueggeman told county commissioners Tuesday.

Money will be taken from other parts of the budget, such as street maintenance and emergency reserves, to keep plowing, officials said.

“Not plowing today is not an option,” said County Commissioner Mark Richard. “We’ll address the deficit in the budget come summertime.”

With another 3 to 5 inches of snow forecast for Spokane on Wednesday night and early Thursday, the sheriff’s office warned that people who shoveled snow off their property and onto streets could be arrested for disorderly conduct.

“While we sympathize with the amount of snow that property owners have to deal with this year, their solution can’t be to dump it on public streets,” sheriff’s Sgt. Martin J. O’Leary said.