The Rogue Valley likely will get a white Christmas this year — not with fresh snow, but rather a shroud of fog, according to the National Weather Service in Medford.
Most of the valley will be socked in through Christmas Day and beyond, said Connie Clarstrom, NWS meteorologist in Medford.
"There is a possibility we will see white Christmas clouds all day ... not your typical white Christmas," Clarstrom said. "What we're expecting is all-day fog or clouds on Christmas Day itself."
Freezing fog was forecast for Sunday and Tuesday nights and Christmas Day, according to the National Weather Service, which could make for slick roads in some areas.
The valley normally is foggy during winter months, Clarstrom said, as high-pressure systems settle on the region, trapping cooler air in the valleys and stranding warmer air on mountain ridges above.
Because the chance of prolonged warm sunlight is slim-to-none this time of year, the area needs a storm system to move in to blow the stagnant air away and clear the valley, Clarstrom said.
"You need that warm sunlight to burn off the fog from above, but ... what we really need is a mixing of the air mass. Sometimes what we have is a weak front will come through and mix the air," she said. "We're seeing high pressure in the area, so it's warmer at the ridges up above the valley, and it's cooler in the valley ... it is fairly common anytime we see high pressure that we will get fog in the valleys."
— Sam Wheeler