An atmospheric river event, bringing large amounts of moisture to the West this weekend, will gradually move across the country and bring hazardous weather conditions to millions of people.
The blockbuster storm will start in the west with heavy snowfall, gusty winds and coastal flooding, then move east, threatening potential blizzard conditions in the Midwest and tornadoes in the South.
“Extreme snowfall is likely in the Sierra and northern California mountain ranges,” the Weather Prediction Center said Saturday. Adding that, “Prolific snowfall rates of 3 inches per hour are expected in the Sierra Nevada, accumulating to over 5 feet through Sunday in some areas.”
More than a dozen western states are under winter weather alert this weekend as the powerful storm system moves through the region.
Snow will be measured in feet in the Sierras, Rockies and Cascades. Heavy rain will also be noticeable on the West Coast, particularly in California, where flooding risks exist through Sunday.
An atmospheric river is a plume of moisture that trickles off the Pacific Ocean. Similar to a fire hose, it sprays moisture into an area for an extended period of time, resulting in very heavy rain or snow.
Most coastal communities will collect 1 to 3 inches of rain over the weekend, and parts of northern and central California could receive 3 to 5 inches of rain total. Coastal erosion and flooded roads will be major concerns.
“Additional heavy rains can lead to isolated runoff issues, especially over recent burn scars,” the Weather Prediction Center said.
Hurricane-force wind gusts of 80 to 100 mph are also possible in the mountain ranges on Saturday, which will bring blowing snow resulting in near-zero visibility and difficult to impossible travel conditions.
“Gusty winds and heavy snow could bring down tree limbs,” the National Weather Service office in Sacramento, Calif., said, which could lead to “near-sail conditions at times.”
And the western United States won’t be the only region affected by the storm.
“As the system moves across the plains early next week, a springtime storm system is developing,” CNN meteorologist Chad Myers said. “Significant severe weather will occur in warm southern air and a major snow and ice event will occur in the western Great Lakes and northern Plains.”
For the Northern Plains and Midwest, the threat of blizzard conditions is increasing as heavy snow, strong winds, ice and freezing rain will all be possible early next week from Colorado to Wisconsin.
“A winter storm is expected to affect the Northern Plains Monday evening through Thursday,” said the National Weather Service office in Bismarck, North Dakota. “Difficult travel conditions are expected Monday evening through Wednesday evening due to heavy snowfall, reduced visibility and windblown snow.”
Heavy snow and strong winds will be the main concerns, but freezing rain and ice are also possible.
If winds are at least 35 mph and visibility is less than a quarter mile for at least three hours, it could bring a full-scale blizzard to the area.
Widespread snowfall amounts across the Northern Plains and Midwest will be 4 to 8 inches, and some locations could pick up more than a foot through Friday of next week.
“While some uncertainty remains, confidence is growing that strong winds and heavy snowfall will produce dangerous impacts across much of the Central/Northern Plains and the Upper Midwest,” the forecast center said. .
Slippery roads and near whiteout conditions will make travel very difficult, if not impossible, in some of these areas. Power cuts will also be possible due to very strong winds.
The threat of severe storms is also increasing in the Southern Plains and Gulf Coast region, including tornadoes, large hail and damaging winds.
“Although December tornadoes are relatively rare compared to spring, they are often more likely in parts of the southeast and lower Mississippi Valley, where there is often a secondary peak in fall and winter,” Matthew Elliott, a meteorologist at the Storm Prediction Center, told CNN.
Severe storm potential begins Monday evening in Oklahoma and northern Texas, gradually spreading into Arkansas, Louisiana and Mississippi on Tuesday.
Severe storms are likely to continue Tuesday night in the Gulf Coast region. Night tornadoes are more dangerous because many people are sleeping and unaware that they need to seek a safe place.
Although the greatest tornado threat exists during the day, there is always the possibility of a few rotating storms during the evening hours.
On Wednesday, the greatest threat exists for an area stretching from New Orleans to Panama City, Florida.
“Details regarding the areas most prone to tornadoes will become clearer as the event approaches and smaller-scale trends become more evident,” Elliott said.
Because forecasts can change, it is important to pay attention to developments in the coming days.