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."
Because of limited air movement, pollutants can be trapped in the Rogue Valley. Air quality was listed as moderate over a 24-hour period Saturday in Medford and Shady Cove.
The only upcoming storm-like disturbances moving inland from the coast are headed toward the southern Willamette Valley, she said, so expect high pressure to linger over the Rogue Valley at least through Thursday.
According to the NWS forecast, Medford, Talent, Phoenix, White City, Central Point and Eagle Point may not see a glimpse of blue skies during the foggy span, but Ashland and foothills surrounding the Rogue Valley are a different story.
In Ashland, as usual, Clarstrom said, the sun will likely sporadically peak through the fog, and it may even get sunny on a few days.
"In Ashland, sometimes we get off-shore easterly winds that blow through that part of the valley and keep the air mixed," she said. "Sometimes they get it (fog), sometimes they don't in Ashland."
Ashland also has a higher elevation, as do homes dotting the higher foothills surrounding the Rogue Valley, she said.
If the lingering fog does persist, it could result in more delayed flights at the Medford airport and limited visibility on valley roads, Clarstrom said.
Within Jackson County's Air Quality Maintenance Area, which can be viewed online at http://ow.ly/rZfB8, there is no open-air burning allowed in November, December, January or February — meaning no open barrel burning and no pile burning.
The county also issues advisories limiting woodstove burning during winter months and high-pressure spans in the area.
Regulations concerning whether burning inside a woodstove is acceptable on any given day can be found at the bottom of the county's webpage at http://ow.ly/rZfKU or by calling 541-776-9000.