A hard freeze is expected to grip Jackson County early next week, but just how cold it gets could depend on the amount of snow that falls. 

A cold air mass is set to push into the area from the north on Sunday, New Year's Day, according to the National Weather Service. That's when the best chance for snow will occur, with anywhere from a trace to 2 inches expected below 2,000 feet.

"If you have travel plans for New Year's Day, you need to be prepared for wintry driving conditions, because nearly all area passes will be affected by snow at some point Sunday," a Weather Service bulletin said. "Once the snow threat is over, the certain part of the forecast is that temperatures will be very cold for most of the week."

On Monday, nighttime low temperatures are forecast to dip down to about 15 degrees in Medford and 13 in Ashland. On Tuesday — expected to be the coldest night — the forecast drops two more degrees for both cities, and some forecasters have mentioned the possibility of single digits. Below-freezing nighttime temperatures are expected to endure the remainder of the week, at least.

The amount of snow that falls could determine how low temperatures go, because snow cover can reflect sunlight.

"If we get closer to the 2-inch mark, it'll get colder than what's forecast," said meteorologist Brad Schaaf. "That allows temperatures to get very cold. If the snow sticks, we could see temperatures get very, very cold."

Weather officials reminded area residents to protect pipes, cover sensitive outdoor plants and keep outdoor pets and livestock in a warm, dry area.

In the meantime, an air stagnation advisory issued Wednesday for the Rogue Valley will continue through about 3 p.m. Friday. According to the Oregon Department of Environmental Quality, the area is experiencing an air inversion, which can trap smoke and particulates near the ground. Officials ask people in affected areas to limit outdoor burning and the use of uncertified woodstoves.

— Reach reporter Ryan Pfeil at 541-776-4468 or rpfeil@mailtribune.com. Follow him at www.twitter.com/ryanpfeil.