More snow, then rain, to be followed by possible urban flooding

It's not over.

We're likely going to see more snow tonight, and when things warm up later this week, there's a good chance of urban flooding as rain and melting snow overwhelm clogged or frozen storm drains, according to Johnny Burg, a meteorologist with the National Weather Service in Seattle.

Tonight, a new system bringing snow, rain and fluctuating temperatures is expected to hit the region. With daytime temperatures in the low 30s expected today, any snow and ice that are already on the ground could partially melt — and then refreeze when the storm hits, making for treacherous driving conditions Wednesday.

Drivers are encouraged to check conditions before hitting the roads for the morning commute. Visit www.wsdot.wa.gov for information.

Metro Transit expects to run only about half its bus routes today, the same as on Monday, said general manager Kevin Desmond. While highway bus routes and those that service park-and-ride lots operated Monday on close-to-normal schedules, problems persisted.

"Seattle really is the largest problem — it's got the most challenging terrain, the most hills and the most demand for service," Desmond said.

The weather has also taken a toll on the bus fleet: Some have been damaged while others — particularly Metro's 60-foot-long articulated buses — have been pulled off the streets because they don't do well in the snow, he said.

In Snohomish County, the Web site for Community Transit was overwhelmed by traffic, so the main page was taken down Monday and replaced with updated rider alerts. For this morning's bus information, visit www.commtrans.org/emergency/.

Christmas Day will most likely be wet, with a 70 percent chance of rain and snow showers. The forecast calls for cloudy conditions with a high of 37 degrees.

"People should get their sledding in now, while they can," Burg said.

Depending on how much snow falls in the mountains, Snoqualmie Pass could be periodically closed Wednesday — Christmas Eve — while transportation crews do avalanche-control work. Drivers should allow at least two hours of extra time to get to their destinations, said Mike Westbay, a spokesman for the state Department of Transportation.

Snoqualmie Pass was closed to oversized loads on Monday but otherwise, traffic was moving smoothly with dry, powdery snow covering the roadway, he said. As of noon Monday, 77 inches of snow was on the ground at Snoqualmie Pass — compared with 174 inches recorded at the end of December last year.

"We expect snow to hit the region (Tuesday) night and the passes really hard on Wednesday morning," Westbay said.

As temperatures warm and snow changes to rain, drivers should prepare "for some really challenging conditions," he said.

The slipperiest conditions occur when temperatures are in the 31- to 33-degree range, Westbay said. "If it's bare and wet, the de-icer gets diluted," he said. If the temperature then drops, the moisture on the road freezes and "it gets really icy."

Seattle got a much-needed respite from the snowfall Monday, with less than an inch of precipitation at Seattle-Tacoma International Airport, said Burg of the weather service.

Snow-removal crews and residents spent Monday digging out from the weekend snowfall that set back-to-back records at the airport on Saturday and Sunday.

Heavy snow was blamed for a roof collapse and gas leak Monday at a mobile-home manufacturing business in Marysville, said Kristen Thorstenson, Marysville Fire Department spokeswoman. No one was injured.

Also on Monday, a Federal Way man, 52, was struck by a car on southbound Interstate 5 in Kent, according to the State Patrol. The man apparently stopped to remove the chains from his tires in the right lane, south of the Highway 516 exit, when he was hit by a car driven by a Sumner man. His condition was not immediately available.

Sara Jean Green: 206-515-5654 or sgreen@seattletimes.com