Rain is on the way Friday, but the lingering effects of the week's weather could still make getting around a challenge.

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When even the official weather watchers start issuing mea culpas and saying things like “the next day or so will continue to be a tricky and complicated precipitation forecast” — in CAPITAL LETTERS, no less — you know the weather is going to be challenging.

Good news first: warming soon. They really mean it this time. Friday’s high is predicted to be 47 degrees with a regular old Pacific frontal system coming in like a pair of warm fuzzy slippers and blanketing us with that familiar, welcome rain, rain and more rain.

Bad news: Presuming the freezing rain and snow predicted for Thursday night materialize, the Friday morning commute will be hell on wheels — again.

More bad news: Snow and ice are falling off stuff. Not just off trees, but off buildings and power lines. And all around the region, trees and power lines themselves are falling.

Downed trees and power lines cut off power Thursday to hundreds of thousands of customers around Puget Sound — sometimes twice.

In Seattle, officials blocked off several downtown sidewalks Thursday night, fearing that ice falling from buildings would hurt pedestrians.

At the Roosevelt Hotel on Pine Street and Seventh Avenue, large sheets of ice crashed to the ground, scaring hotel guests but not injuring anybody, an employee said. The sidewalk was blocked off afterward.

At the National Weather Service, there was chagrin about off-base forecasts that first predicted a huge storm, then backed off a bit snow-wise, and finally incorrectly forecast a Thursday return to warmer weather.

“We were about a day early with the warm-up,” said meteorologist Dennis D’Amico, who said he and colleagues “felt the vibe” of irritated critics.

Predicting winter precipitation in the lowlands is often tricky, he said, but the combination of models and interpretation led meteorologists astray until very early Thursday, when they realized the problem and issued a rare ice-storm alert.

“We underestimated how much that cold air would really stick in place,” he explained. “We had cold air at the surface, then we had warmer air riding up over that colder air.”

That, it turns out, is a recipe for freezing rain. “Freezing rain is a snowflake that fell, went through a warmer layer, melted and became rain, then went to a colder layer near the surface, and freezes on contact. That’s the nice ice you scraped off your car.”

Even Cliff Mass, a University of Washington professor of atmospheric sciences who writes a popular weather blog, issued a broad “mea culpa.”

“Well, folks, this is not my profession’s finest hour,” he wrote Thursday. “Our models did not indicate that the precipitation would move so far north, so fast.”

Then it all gets kind of technical, when most folks really just want to know whether they can drive to work or not.

D’Amico predicts that by Monday, you’ll be able to drive comfortably, depending on where you are.

For Friday, Metro buses will continue a snow schedule.

Amtrak passenger service is suspended between Portland and Seattle because of scores of fallen trees and other debris on the tracks.

Service north of Seattle to Vancouver, B.C., and south of Portland to Eugene, Ore., continues, subject to weather-related delays.

What will happen on the roads Friday morning is unclear: Will an overnight melt happen in time to plow away the slush on the roadside? Will puddles make speeding traffic hydroplane and crash?

Flooding — on roads and everywhere — poses the next threat, as a series of storms over the next week brings more rain, adding to the snowmelt.

At Seattle-Tacoma International Airport, all three runways were open Thursday night and operating “normally,” said Charla Skaggs, spokeswoman for the Port of Seattle. However, airlines make their own decisions about whether flying into the area is safe, and many were still canceling flights into Seattle.

Alaska Airlines and Horizon Air said weather has forced the cancellation of 50 flights Friday. That’s in addition to the 310 flights to and from Seattle canceled by early evening Thursday, affecting 29,000 passengers; only 15 of Alaska’s 114 daily flights and one Horizon flight had departed Seattle by that time.

For those with a way with words, this storm had a certain inspirational quality. For some, it evoked the film “Groundhog Day.”

“It’s like a storm in slow motion that keeps happening again and again,” said Puget Sound Energy spokesman Roger Thompson.

It also pumped up some creativity among those posting comments on Twitter, particularly those about how this storm has morphed from one thing to another.

The Bellevue Reporter noted that the “hashtags” — a # plus a short name used on Twitter to help identify different threads of conversation — have changed as the storm progressed. In a condensed way, they tell the story of what we’ve been through:

“It started with #WAsnow, then it was #WAice, now we have #WAsnow, on top of #WAice, on top of #WAsnow. #snOMG.”

Friday, it will all turn to #waSLUSH.

Seattle Times staff reporters Mike Lindblom, Brian Rosenthal and The Associated Press contributed to this report. Carol M. Ostrom: 206-464-2249 or costrom@seattletimes.com. On Twitter @costrom.