How an atmospheric river is impacting the West Coast

An atmospheric river is slamming the West Coast, bringing intense rain, winds and snow that could make for treacherous conditions.

Atmospheric rivers are like "rivers in the sky," according to the National Oceanic and Atmospheric Administration. The long, narrow regions in the atmosphere carry large amounts of water vapor over the Pacific Ocean, which is released as rain in lower elevations or snow in higher elevations when they make landfall. The events are "tied closely to both water supply and flood risks," NOAA said.

More than a dozen states in the West are under weather alerts from this storm, which is bringing damaging winds and flood risks from Washington state down to California Tuesday into Wednesday.

"As a deep layer of moisture streams onshore it will help spread a few inches of rainfall/feet of snowfall at elevation possible along the coastal areas and south into central California throughearly Wednesday morning," the National Weather Service said. "The pattern will present the possibility for widely scattered instances of flash flooding are possible at lower elevations, particularly in burn scars."

Flood concerns

Flood watches and advisories have been issued from Seattle to the San Francisco Bay, with up to 6 inches of rain possible in some locations. Flooding caused by "excessive rainfall" is possible in portions of northern and central California.

Areas along the coast of Oregon have already reported 2 to 4 inches of rainfall. Hoodoo Ski Area, a ski resort in the central Cascade Range of Oregon, said it be closed Monday and Tuesday "due to excessive rain."

There have already been several reports from law enforcement and the public of roadway flooding Tuesday in Seattle and in several California cities, including Salinas, Clayton and Gonzales, with vehicles reported to have been getting stuck.

Extreme rainfall from an atmospheric river can cause mudslides, NOAA warns.

Strong winds and high surf

The system has brought strong winds as it moved ashore this week. Heavenly Ski Summit in California, south of Lake Tahoe, recorded a 111-mph wind gust overnight.

Wind advisories are in effect for parts of northern and central California, with the National Weather Service warning of downed trees and power lines and power outages possible. Nearly 200,000 customers from Washington to California are without power as of midday Tuesday, with most in Oregon, according to PowerOutage.us.

High surf advisories have also been issued along the California coast. Large breaking waves of up to 26 feet are forecast in Northern California throughout Tuesday.

Heavy snowfall

Winter storm warnings have been issued from California to Colorado, where some areas could see up to 40 inches of snow. Avalanche danger is high, with five states under avalanche watches and warnings -- California, Nevada, Colorado, Montana and Idaho.

Into the rest of the week, a "significant atmospheric river storm will bring renewed impacts" to the greater Lake Tahoe area Friday through early Sunday morning, according to the National Weather Service, including heavy rain and snow.

ABC News' Max Golembo and Kenton Gewecke contributed to this report.