Storm wallops West. Will it bring East coast first Christmas snow since 2002?

A deluge of Pacific rain – as much as 20 inches in some places – could trigger mud slides in the Los Angeles hills over the next several days, before becoming a major storm event likely to blanket much of America's northern belt with snow just in time for Christmas.

An early winter snow and ice season just got a little more peculiar over the weekend, as a weakening regional high-pressure system over the Pacific allowed huge pockets of warm moisture onshore as part of a weather effect seen only every 10 to 15 years, meteorologists say.

The storm dropped 2.3 inches of rain in Los Angeles – an amount not seen in the dry valleys since 1921. By the time it reached California's higher altitudes, the rain had turned to snow, dropping 9 feet of the white stuff on Mammoth Mountain. Continuing heavy rains could yield to flooding throughout the coastal West in the next few days, as well as powder conditions for the region's skiers.

A "snow blitz" had already covered much of the upper Midwest with snow two weeks ago, collapsing the roof of the Minneapolis Metrodome for the fifth time. An early freeze sent Southerners indoors, damaged citrus crops in Florida, and turned much of Atlanta into a demolition derby as black ice formed last week at the height of rush hour.

In the east, a high-pressure oscillation situated over Greenland has forced more Arctic air than usual down from Canada, creating unusual early winter conditions throughout the East – the same system that has brought blizzards to Britain and Scandinavia.

A diminished regional high-pressure system over the central Pacific, which usually helps divert storms away from California and up into Washington and Oregon, means the West, too, is beginning to see some unusual weather, reports the Los Angeles Times.

Meteorologists expect the snow to track into the Midwest by midweek, with up to six inches possible for the Minnesota Vikings-Chicago Bears football game (to be held at a college stadium because of the damaged Metrodome) on Thursday. The front is likely to continue eastward and could drop copious amounts of snow on cities like Boston and New York by Christmas Day. Those cities haven't seen a white Christmas since 2002.