ATLANTA — Gov. Brian Kemp announced a state of emergency for all Georgia counties Thursday ahead of a winter storm expected to dump snow and sleet onto the northern third of the state starting Saturday, potentially encasing the land in a layer of ice.

In an online briefing from Belgium Thursday, where he was traveling to promote trade, Kemp outlined state preparations for a wintry mix that could slicken roads and pull down power lines, darkening homes for days if temperatures remain as cold as predicted.

The governor said he had called up 500 National Guardsmen for deployment, if necessary. State agriculture and forestry crews are prepared with chainsaws to clear the way for power crews.

His main message: hunker down for the weekend.

“If you can just stay off the roads, that would be a big favor to us,” he said, noting that state police, utility crews and salt trucks need open roads to do their work.

The latter will begin brining roadways late Friday night or early Saturday morning. The governor placed the danger zone north of Interstate 20.

The National Weather Service has a winter storm watch in place in an east-west line just north of the Atlanta suburbs, dipping south as it moves to the east side of Georgia to take in Athens. The forecast calls for “heavy” mixed precipitation of up to two inches of snow and sleet, with ice accumulations of a quarter to three quarters of an inch.

Major potential impacts include travel disruptions and power outages as ice weighs down power lines and tree limbs that can break and fall on them.

Kemp said a drop in expected temperature of just a degree or two could push the danger line southward.

Josh Lamb, director of the state emergency management agency, advised filling cars with gas and emergency supplies, including snacks and blankets, and to drive cautiously on bridges and overpasses, which tend to ice up faster. But he also encouraged people to stay off the roads.

Lamb said Georgians should prepare their homes by covering pipes, cleaning gutters and stocking a three-day supply of food and water.

Prepare a way to keep cellphones charged while devising a communications backup plan for family members, he said. “Take precautions, don’t panic, and please stay informed and stay off the roads.”