UPDATE Friday 8:45 a.m.:

Caltrans crews are reopening northbound Interstate 5, and the California Highway Patrol is running escorts to assist northbound motorists. Southbound traffic is reportedly flowing freely.

The next few days are expected to see relatively clear weather, with patches of frost and overnight lows around 28 degrees in the Santa Clarita Valley.

Friday brings a diminished 20 percent chance of snow to the Grapevine with overnight lows of 20 degrees at Lebec, followed by mostly sunny skies Saturday and slightly warmer temperatures.

UPDATE Friday 8 a.m.:

Grapevine remains closed at Parker Road due to icy road conditions. The California Highway Patrol provided escorts for about 500 vehicles that were trapped overnight in the closure area.

Thursday 4:30 p.m.:

The California Highway Patrol shut northbound Interstate 5 at Parker Road in Castaic shortly after 4 p.m. Thursday due to poor driving conditions over the Grapevine.

CHP officers were diverting northbound traffic off the freeway at Parker Road.

Southbound I-5 is also shut north of Tejon Pass.

Snow is reportedly falling at Templin Highway, where access to I-5 has been restricted.

I-5 was had been closed in the early morning hours Thursday due to snow but re-opened in the late morning when the snow turned to slush. Many drivers subsequently lost control of their vehicles in the slush and careened across freeway lanes. Some crashed into the center divider while others overturned.

Lebec was reporting 24 degrees with snowfall at 4:30 p.m. The National Weather Service has issued a winter weather advisory for the area with snow levels predicted to fall as low as 1,500 feet. The advisory is in effect until Friday at 4 p.m.

Accumulations of 2 inches are expected at the 2,000-foot level, and 2 to 3 inches above 4,000 feet. The Tejon Summit is higher than 4,000 feet.

North winds of 20 mph to 30 mph in the foothills and stronger winds up to 50 mph through the passes are causing additional wind chill.