A pair of back-to-back storms were forecast to dump heavy snow and rain over parts of the Pacific Northwest, northern California and the Rockies this week, triggering winter storm and flood warnings.

The storms pushing off the Pacific are the result of an atmospheric river, a corridor of air heavy with moisture that forms when warmer air from the tropics moves toward the poles.

As the first of the two storms pushes inland on Monday, it will bring heavy coastal rain and snow to the highlands across the Pacific Northwest and northern California, according to the National Weather Service. By the evening and into Tuesday, the wintry mix is expected to spread across the northern Rockies and Great Basin, bringing as much as 8 to 12 inches of snow to the Cascades.

The next storm is expected to approach the Pacific Northwest Tuesday night, unleashing showers and thunderstorms along the coast and portions of the Coastal Ranges that have the potential to trigger flooding. As the storm moves east, it could bring more snow to the Cascades.

"Rainfall totals could be as high as 3-4 inches in the Olympics and 1-2 inches for Seattle and Portland," said Elizabeth Danco, a meteorologist with AccuWeather.

The weather service office in Seattle warned residents about potential river flooding this week.

"There is little break between each system. As a result, several rivers are forecast to reach Action Stage with Minor flooding possible, especially by Wednesday or Thursday," the outlook said. "Flooding extent will depend on rainfall rates, temperatures, snow levels, and total rainfall with each of these weather systems next week."

Winter storm warnings were active across multiple Western states early Monday. In central Oregon, weather officials urged residents to remain cautious as they anticipate between 8 to 16 inches of snow and wind gusts as high as 50 mph.

"Travel could be very difficult. The hazardous conditions could impact the Monday morning and evening commutes. Gusty winds could bring down tree branches," the weather service in Medford, Oregon, wrote in a winter weather advisory that could be extended Tuesday. Similar warnings were issued in parts of Washington, northern California, Utah and Nevada.

In the northern hemisphere, atmospheric rivers typically occur during winter and are often cited for strong storms in the West. According to NASA, they are the largest transport mechanisms of fresh water on Earth.

Storms loom after record-breaking snow in Las Vegas, other cities

The atmospheric river approaching the northern West Coast is set to arrive as residents in some areas were still digging out of record-breaking snowfall wrought by a winter storm last week.

In Colorado, Lincoln and Elbert counties received historic snowfall between Tuesday and Saturday, with areas picking up 35.5 and 41.5 inches of snow, respectively.

From Wednesday to Friday, New Mexico's Colfax County was blanketed in 40 inches of snow, while parts of Albuquerque received 7.5 inches of snow. New Mexico Gov. Michelle Lujan Grisham issued a state of emergency, unlocking $1.5 million in state funding to support agencies responding to the winter storm.

Part of Las Vegas saw over 30 inches of snow last week, breaking a decades-old record and prompting road closures and power outages. The weather service office in Las Vegas on Monday warned of strong wind gusts that could cause "tree and power line damage" and create "hazardous travel conditions."

Rain is forecast for Eastern states as wildfires rage

Meteorologists project showers and thunderstorms will span much of the eastern U.S. this week, from New England to the Gulf Coast, though it won't be enough to curb the ongoing wildfire threat in the Mid-Atlantic.

Ahead of a cold front on Monday, heavy rain was expected across the Carolinas and the central Gulf Coast. A secondary front was likely to unload rain throughout the interior Northeast, including Upstate New York and New England.

The storms follow showers that reached the Atlantic coast Monday morning after dropping 0.17 inches of rain in New York City, the most rainfall the metropolitan area has picked up since late September. Over the weekend, wildfires led to hazy skies and air quality alerts throughout the nation's most populated city.

The Mid-Atlantic region is grappling with a historic dry spell. New Jersey and Delaware reported their driest October on record, according to the weather service. Meanwhile, The city of Trenton, New Jersey, recently broke the record for consecutive days without rain set in 1903.

"This sort of rain is certainly not enough to really help out with the ongoing drought conditions, but it would be enough to soak the top layer of the soil and brush, which will reduce the chance for blowing dust behind the front and wildfire ignition and spread on Monday as westerly winds pick up," said Brett Anderson, a senior meteorologist with AccuWeather.

Contributing: John Bacon, Dinah Voyles Pulver.