A major storm just prior to Christmas will cause travel disruptions due to drenching rain and heavy snow from California and Oregon to Arizona, Utah and Idaho.
The late-week storm will follow a dose of rain in the deserts and a bit of snow and ice in the mountains of the Four Corners states into Thursday night.
The storm will push southward over California during Friday and Friday night as well as eastward over the interior West spanning Friday night and Christmas Eve.
Enough rain can fall on coastal and low-elevation areas of California, southern Nevada and Arizona to bring the risk of isolated flash flooding and mudslides. The risk of flooding will be greatest in urban areas, while the potential for mudslides will be greatest in recent burn areas.
As colder air circulates in with gusty winds, snow levels will lower in the mountains. Motorists should anticipate poor visibility and slippery conditions over Siskiyou Summit, Donner Pass, Cajon Pass, Tejon Pass and the high ground in Arizona.
Enough snow to shovel and plow can fall on cities such as Flagstaff, Arizona; Boise, Idaho; Salt Lake City and Elko, Nevada.
Conditions will improve from west to east across the region from Christmas Eve to Christmas Day as the storm strengthens and takes aim at the Great Plains with blizzard conditions in the north and severe thunderstorms in the south.
Some last-minute shoppers and travelers may still have to contend with chilly showers in California on Saturday. Gusty winds will cause blowing and drifting snow on Sunday over parts of the Intermountain West.