A storm is expected to drop up to 2½ feet of snow on the northern Oregon Cascades, adding to a snowpack that is well below normal for this time of year.

The National Weather Service has issued a winter storm warning for areas above 4,500 feet. The warning lasts from 4 p.m. Wednesday until noon Friday.

The warning says heavy snow is expected above 4,500 feet, with the heaviest accumulations above 5,550 feet.

Timberline Lodge, for example, is at 6,000 feet. Government Camp is at 3,980, according to the weather service.

Related: What’s new at Mount Hood, Mt. Bachelor ski resorts?

Forecasters said 15 to 30 inches of snow could accumulate. Wind gusts are expected to reach as high as 45 mph.

The state’s three most prominent ski resorts are open for the season, but Oregon’s low snowpack none has a base of over 25 inches.

Much of the state's snowpack is well below normal for this time of year.

Snow levels will gradually drop Wednesday night, and snow will begin to accumulate on mountain passes.

“Travel could be very difficult to impossible,” the winter storm warning cautions.

The warning urges people who must travel through the mountains to keep a flashlight, food and water in their cars in case of an emergency.

Travelers can keep tabs on road conditions by monitoring tripcheck.com.

-- Jim Ryan; jryan@oregonian.com; 503-221-8005; @Jimryan015

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