A winter storm warning will remain in effect from Tuesday morning until Wednesday evening in the southwest and northwest San Juan Mountains.

Ten to 18 inches of snow is possible at higher elevations the National Weather Service said, and winds could reach 40 mph. The storm is expected to hit all mountain passes in the San Juans.

Affected highways include U.S. 550, Colorado 145 and 149. Affected towns include Rico, Telluride, Hesperus, Silverton and Ouray.

Light to moderate snow is expected to begin Christmas morning and increase in intensity late Christmas Day and into Wednesday. Rain and snowfall are expected in the valleys.

Holiday travel will be very difficult because of heavy and blowing snow and reduced visibility, the weather service said.

Forecasters said the strong storm system will move inland over California tonight and then across northern Arizona and New Mexico Christmas Day through Wednesday. The core of the storm system is expected to hit areas just south of Utah and Colorado, but wintry weather is still expected across a large portion of eastern Utah and Western Colorado. The San Juan Mountains have a winter storm warning in effect through Wednesday, and the mountains of eastern Utah and Western Colorado could receive 6 to 12 inches of snow mainly Christmas night through Wednesday.

There is still some uncertainty where the heavier bands of snow might set up, but it is likely that most valleys will see 1 to 2 inches of snowfall, with amounts increasing as elevation increases into the mountains.

In Montezuma County, there’s a 50 percent chance of snow on Christmas, and a 70 percent chance of snow on Tuesday night. One to 2 inches was expected. High temperatures on Christmas were expected to reach 45 degrees and fall overnight to a low of 28 degrees.

Forecasters said there’s a 50 percent chance of snow on Wednesday, and a 20 percent chance on Thursday.