The snow might be winding down, but Thursday morning's commute is expected to include frozen and slick roadways throughout Western Washington.

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Snow + rain = slush. To this easy equation, add brisk, below-freezing temperatures overnight and a bit of freezing rain, and what do you get early Thursday?

Trouble, in the form of frozen slush and ice — conditions that likely will force morning commuters to brave a daunting gantlet of slippery crud to get to work.

Almost makes you wish for rain, doesn’t it?

That’s coming, too. Just wait. A weak storm on the heels of Wednesday’s snow-dumper will hit Thursday, but the National Weather Service says it will produce no more than an inch of snow.

By Thursday night, there will still be a chance of snow, but lows in the Seattle area of about 34 degrees should start the big melt — fueling already widespread fears of urban flooding.

“It is confusing,” said Dennis D’Amico, a meteorologist with the National Weather Service. “We have one system back to back with this one. The next one coming in is not very strong; it’s not going to produce nearly so much precipitation, and it’ll be warmer.”

The South Sound area took on the most snow Wednesday, with more than a foot reported in Olympia and Centralia, and up to 20 inches in Napavine, Lewis County. Six inches were reported at SeaTac, and areas of Seattle got 4.

D’Amico and other weather-watchers worry that people who heeded warnings and stayed off the roads Wednesday will try to head to work Thursday.

“Conditions on the roadway are already poor, and the last thing we want to add to that is a freezing situation,” said Julie Startup, spokeswoman for the State Patrol in King County.

Of course, none of us want the Snow-No-Go reputation we have among those from Minnesota and snowier parts. Still, troopers responded to a total of 726 collisions between 9 a.m. Tuesday and 9 a.m. Wednesday, said Bob Calkins, spokesman for the State Patrol in Olympia. For some perspective, note that troopers went to 83 collisions in the same 24-hour period in 2011, a day without snow.

Then on Wednesday, lots of folks stayed home, and crash totals dropped dramatically.

Trooper Keith Leary said that even though road lanes were mostly bare and wet, many suburban stretches still had snow between lanes or on shoulders where cars spun out. In one case, a sedan wedged halfway underneath a beer truck, and in another, a semi spun out in downtown Bellevue toward the left shoulder of I-405 southbound.

Although roadways in Seattle treated with brine appeared slushy but passable at midday Wednesday, according to a Seattle Times spot-check, that could change dramatically with expected overnight freezing temperatures.

The Seattle Department of Transportation said it began plowing and spreading rock salt to main arterials starting Wednesday morning in an effort to prevent ice from forming. Seattle DOT said it would continue 24-hour snow-removal operations.

Still, there’s a good chance that people could wake up to icy roads anyway, said Barb Graff, director of the city’s Emergency Management Department.

“We’re trying to manage it aggressively,” Graff said. But there were too many variables to predict just what the morning commute would look like, she said.

As of Wednesday afternoon, the city had not yet called in crews from Seattle Public Utilities or the Parks Department to add to its plow force.

Graff said the city would rely on cameras and feedback from transportation crews and police and firefighters in the field to determine whether conditions had become icy. Commuters also can report icy conditions to the city’s transportation hotline at 206-684-7623.

By Wednesday afternoon, the Seattle Police Department had closed off more than two dozen roads, most of them too steep to navigate safely. Some of those roads are too dangerous to treat or clear, and will probably remain closed until the weather warms up and melts the snow, said SDOT spokesman Rick Sheridan.

Winds — which reached 85 mph at the top of Crystal Mountain ski resort Wednesday and 95 mph at Newport on the Oregon Coast — should drop dramatically Thursday, the National Weather Service said.

But morning ice could be a nuisance for Sounder train commuters.

Sound Transit canceled its 3:50 p.m. train from Seattle’s King Street Station to Tacoma, and the 5 p.m. return trip to Seattle, because of “switch issues.” Others were on schedule. BNSF Railway, which owns and maintains the tracks, has crews in place to defrost the switches, trying to say ahead of nature, BNSF spokesman Gus Melonas said earlier. Wednesday morning, Sounder trains operated smoothly, and Melonas said freight trains were able to cross Washington state all day.

East of Lake Washington, road crews were busy Wednesday. Bothell, which tends to be heavily hit because it’s in the “convergence zone” north of Seattle, received 6 inches or more of snow. But all main roads stayed open, including winding Highway 527 through the woods north of downtown. Even steep 228th Street Southeast stayed open.

Bellevue road crews have been busy, with the hills south of I-90 absorbing 6 inches of snow, deputy utilities director Mike Jackman said. Bellevue was able to keep the steepest arterials open, including Lakemont Boulevard Southeast and Somerset Boulevard Southeast. The goal now is to stabilize the streets by reapplying salt, then pushing the slush off to the roadside as much as possible, before it refreezes into blocks of ice.

These kinds of slush-bergs were a stubborn problem for Seattle in December 2008, when unsalted snow melted, reshaped and refroze for days on certain streets. Seattle now spreads salt brine and granules, and occasional sand.

Downtown Bellevue streets are in very good shape, Jackman said. Crews were to continue overnight and to start extending the work into neighborhood streets around midnight. Kirkland closed additional roads late Wednesday, including Northeast 116th Street, a busy east-west route just uphill from the Juanita area.

Fearing that bus drivers and parents will have trouble navigating icy streets, Seattle Public Schools canceled all classes and after-school activities for Thursday. Most other school districts around Puget Sound arrived at similar decisions, although a couple were planning to operate on a two-hour delay.

University of Washington also canceled classes for Thursday.

In the mountains, avalanche danger is high, the weather service said, with lots of heavy new snow poorly bonded to the crusty older snow, and likely more dense snowfall or rain helping loosen the bonds. The avalanche report said there was high danger and described slides as increasingly large and fast.

Now, attention is turning to the risks to come: Icy branches falling on power lines, and flooding as the pile of snow melts.

Scattered power outages were reported, including in Snohomish, Shoreline and Tacoma, with about 16,000 homes without electricity late Wednesday.

Melting, too, will pose difficulties. Seattle transportation officials asked residents to help clear storm drains on their streets if it can be done safely. Pierce County officials asked residents to shovel snow from walkways and driveways.

Late Wednesday the freezing rain started as the storm was winding up, leaving behind scattered power outages, damaged fenders and a King County snow plow that tangled with a power line — and these amazing stories:

A Graham couple took so much time getting to the hospital their second son was born inside a hospital elevator, which took that moment to get stuck between floors. Three nurses were in the elevator car with Katie Thacker, the mom, and baby Blake — 7 pounds, 15 ounces — came along just fine.

Then there was the sledding. Which can be dangerous. Especially if you’re an adult, if alcohol is involved, and you’re zooming through the Hoquiam city cemetery on an 8-foot plastic boat. A 21-year-old man who tried that apparently broke his leg, Hoquiam police said. The good news: The “sled” turned out to be a fine stretcher to help haul him to the hospital.

Seattle Times staff reporters Jack Broom, Susan Kelleher, Mike Lindblom, Brian M. Rosenthal, Jennifer Sullivan and Craig Welch contributed to this report. Carol M. Ostrom: 206-464-2249 or costrom@seattletimes.com. On Twitter @costrom.