Snow and high winds are expected to combine into a blizzard Saturday night and into Sunday in Portage Valley and along Turnagain Pass, according to the National Weather Service.
"Travel will be very dangerous to impossible," the weather service said. "Do not travel."
The service early Saturday issued a blizzard watch that it upgraded to a warning Saturday afternoon. The storm is expected to hit around 9 p.m. Saturday and end around 6 p.m. Sunday.
The warning covers western Prince William Sound and parts of the Kenai Peninsula including Whittier, Seward, Girdwood and Moose Pass.
People in the area should expect whiteout conditions. Snow accumulations of 8 to 12 inches are expected and some localized areas could get 20 inches, the weather service said.
A watch means forecasters see strong potential for severe weather but aren't certain it will hit. A warning means a storm or other weather extreme has arrived or is expected soon.
Winter storms are expected in other parts of Alaska too, from St. Lawerence Island to Southeast, as 2017 nears its end.
In Portage Valley and Turnagain Pass, trees and power lines could fall or be damaged. Drifts could be significant, the weather service said.
Winds could gust up to 60 mph with blowing snow making driving difficult. Visibility could be less than one-quarter mile.
The winter storm is expected to continue into Sunday with more snow in the morning and snow and rain in the afternoon, the weather said.
The National Weather Service also has issued warnings, watches or advisories for severe weather in other parts of the state.
A blizzard warning is in effect from Saturday night through Monday morning for St. Lawrence Island and the Bering Strait coast. The Yukon delta and western part of the Kuskokwim delta were under winter weather advisories Saturday, and on the Yukon, challenging conditions were expected to continue into Sunday.
A front moving east across the Gulf of Alaska was expected to dump snow across Southeast Alaska from Yakutat to Metlakatla on Sunday night and into Monday, according to a special weather statement.
A blizzard occurs when a snowstorm lasts at least three hours with sustained or frequent winds of 35 mph or higher. Falling and blowing snow reduces visibility to one-quarter mile or less.
You can find weather conditions for your community on the National Weather Service website.