Notoriously slippery freezing rain might pelt Medford, Ashland and other cold pockets of the Rogue Valley this evening, the National Weather Service reports.

Notoriously slippery freezing rain might pelt Medford, Ashland and other cold pockets of the Rogue Valley this evening, the National Weather Service reports.

"We have cold air that is trapped in the valley and we're not sure when that's going to clear," meteorologist Misty Duncan said, explaining that there is a layer of warm air above that, which makes the chance for snow slim to none.

"If the rain falls through the warm air and then through the cold air, it's likely to freeze," she said.

The Weather Service office in Medford is posting a 60 to 70 percent chance of freezing rain to fall between 4 p.m. and 10 p.m.

But that's a worst-case scenario, which the Weather Service models spit out purposely, said NWS meteorologist Shad Keene.

"Really, it's about a 25 percent chance of freezing rain that will have significant impact ... but it could cause a serious problem, because we just don't get it much," Keene said.

Across the valley at around 4 p.m., the temperatures will range between about 34 to 35 degrees, he said, with potentially colder temperatures lingering near creek beds and heavily shaded areas.

"It's going to be so close, the margin of error is just going to be a few degrees," Keene said.

After 10 p.m., the temperature will hopefully climb above freezing as the valley's blanket of cold air disperses, Duncan said, then, the freezing rain will turn to water.

The Weather Service isn't expecting a dramatic amount of ice to accumulate on the roadways, except in shaded areas that haven't thawed over the past few days.

"Any areas that haven't been in the sun for the last few days will probably have ice accumulation," Duncan said. "It's kind of just concentrated in the valleys where the cold air is still stuck."

There also is a good chance of freezing fog until 1 p.m., the National Weather Service office in Medford reports.

Road crews can't work any harder than they have been since Friday, and are doing all they can to clear the roads of as much snow and ice as possible before the potentially ultra-slick conditions hit, officials said.

"This is where drivers are going to get caught ... it will probably fall as rain and land as ice," said Gary Leaming, spokesman for the Oregon Department of Transportation.

"We're going to have a lot of roads and highways that are going to be in the shade," he said. "It may not be readily apparent that the pavement is going to be slick."

In 2009, the last time freezing rain fell across the Rogue Valley, Ashland Fire and Rescue Battalion Chief Scott Hollingsworth was responding to a motor vehicle accident above town in a chained-up fire truck, and started sliding backwards down a hill, he said.

"If freezing rain does occur, Ashland's snow-covered streets will become very icy ... gravel and traction devices such as chains will not mitigate the hazardous conditions," said a press release sent out by the city Wednesday afternoon.

After four consecutive snow days, the Ashland School District decided it will hold classes today, but start an hour later than usual, an official there said. Other school districts across the Rogue Valley will make the decision by 6:30 a.m.

Between Friday and about 5 p.m. Wednesday, AFR's ambulance went on 114 calls, Hollingsworth said, mostly in response to motor vehicle crashes.

On Friday, when the winter storm landed in the Rogue Valley, the Ashland Fire and Rescue ambulance went on 26 calls, 23 on Sunday. On Tuesday it went out 22 times. The average for a day's work is 10, Hollingsworth said.

John Peterson, street department supervisor for the city of Ashland, said his crews have been working nonstop sanding roads and scraping off whatever ice and snow they could from roadways, but the roads on hills and portions of the town's main thoroughfares are still very slick.

The state is in the same boat, said Jeremiah Griffin, assistant district manager for ODOT's Region 3 in Southern Oregon.

"We've been full force since Friday. Our crews worked through the weekend and we haven't had a break," he said. "We've been working really hard to make sure we can get the roads as clear as possible ... we've had to use every tool in our toolbox."

The tricky problem for motorists with patchy freezing rain is that it's hard to detect, he said.

"The snow is a very visual storm, but the ice and the freezing rain is not very visual; you might feel it with your car first, and it could be too late," he said. "Slow down, obviously, and be prepared for slow traffic. Make sure you leave additional room between your vehicle and the vehicle in front of you."

Friday's forecast calls for a 20 percent chance of rain before 10 p.m., after which a high of 46 is expected, according to the National Weather Service forecast.

Reach reporter Sam Wheeler at 541.776-4471 or Follow him on Twitter @MTwriter_swhlr.