Sonoma County on Tuesday braced for the coldest temperatures of the fall. Men and women hustling down Santa Rosa Avenue tugged their parkas and trench coats closer. Area nurseries pulled protective covers over delicate plants. And homeless shelters prepared for a rush of people seeking a warm place to spend the night.

Expect freezing temperatures on Wednesday and Thursday mornings, the National Weather Service warned.

"It's gonna be cold," said forecaster Bob Benjamin, adding that temperatures could be at or near record lows. He predicted a low of 28 degrees in downtown Santa Rosa Wednesday morning, with temperatures only climbing to 50. The thermometer is expected to sink to 26 Thursday morning before reaching a high of 48. The record for both days is 24 degrees, according to Press Democrat records. At the Santa Rosa airport, temperatures could be even lower, bottoming out at 24 degrees Wednesday morning and 22 Thursday morning.

And in the valleys outside Santa Rosa, thermometers could register in the teens. There is a chance of light, cold rain over the weekend and even snow at elevations above 2,000 feet.

Temperatures are only expected to warm by a few degrees later in the week, Benjamin said. He warned that roads could be icy on Saturday morning, especially in mountainous areas.

Officials urged people to cover exposed pipes with old towels or rags to keep them from bursting, cover sensitive plants and make sure pets have some kind of shelter.

"It's not going to be one of the most comfortable weekends," Benjamin said.

Sonoma County's emergency shelters were mostly full Tuesday, when cold weather apparently drove a Sebastopol homeless man to check for unlocked front doors of homes near downtown. The man, who was barefoot, told officers he'd wanted to get into a house to get warm and sleep.

He also said he'd hoped to find a coat, but apparently could not find a home with an unlocked door, said Sebastopol police Sgt. Mike Nielsen.

Officers found the man on South Main Street but did not detain him. The resident who reported him didn't want the man arrested and officers didn't witness a crime.

The Redwood Gospel Mission in Santa Rosa already is filled to capacity. "This year is a big challenge because we, like every other organization, have been absolutely full," said Jeff Gilman, the executive director. "As it is, we're already sleeping people on the floor."

His organization can handle 150 people in its four shelters. It often takes in people who can't find another place to stay. But Tuesday night, Gilman expected they would be able to accommodate only two or three more people.

Nurseries and farms also were preparing Tuesday for the coming cold.

Harmony Farm Supply & Nursery outside Sebastopol and King's Nursery in Santa Rosa were moving their sensitive plants under overhangs and into enclosed areas.

"We're covering our tender plants," said Susan Hatch, a manager at King's Nursery. Residents can cover their own delicate plants with frost protection blankets that allow light and air in and keep frost out, Hatch said. They can also spray plants with a frost protectant, move them inside or place them under overhangs.

In one low-lying area outside Sebastopol, workers at Laguna Farm hurried to harvest fennel and broccoli that could be damaged by the freeze.

The 25-acre farm grows produce year-round, so cold temperatures are a fact of life, said co-owner Jennifer Branham.

"We're expecting flood and frost at any time,"she said. "But that doesn't mean we want to leave (the produce) out there to freeze."

She said frost actually plays a helpful role, causing turnips and carrots to "sweeten up wonderfully" and killing unwanted vegetation that can then be turned back into the soil for next year.

"There are a few things we're going to have to rescue, but we don't wish the frost away," she said.