A series of fast-moving storms in the Pacific will bring torrential rain, heavy, wet mountain snow, potentially destructive waves and gusty westward winds through this week.
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These storm systems, powered by an atmospheric river, will bring widespread rain, high altitude snow, and gusty weather.
(MORE: What is an atmospheric river?)
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Below is where the heaviest rain and snow occurs in the mountains.
When will rain and snow come to the West?
This mountain rain and snow will arrive in waves as each of these storms moves toward the shore. Let’s break down the timing, day by day, below.
These are subject to change, so check back with us often as this section is updated:
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Monday: Mountain rain and snow will move to the Intermountain West. The evening brings an increased risk of snowfall at higher elevations, particularly in the Sierra Nevada and Rocky Mountains.
There’s even a chance of rain from Southern California, but it’s not more than an inch. The southern Sierra Nevada is expected to see snowfall totals between 1 and 2 feet by the end of the day Monday.
Tuesday: This round of rain and snow will continue eastward as another storm approaches the West Coast. Grounds along the coast will be softened by the first rains from the storms, so the risk of flooding is greater than in previous days.
Mountain snow chances will also increase as cooler air sets in, so another shot of snow for the Sierra Nevada and Cascades is expected as the sun sets.
The first round of mountain rain and snow will extend from the Four Corners to Montana, with rain, snow and a mix of sleet also possible.
Wednesday: The next storm will approach land near Northern California, so the bulk of the heavy rain and mountain snow will be concentrated in the Sierra Nevada. Temperatures will remain below average, so snow levels in the mountains will be lower at higher altitudes. Snow is also expected again in the Intermountain West by the evening.
How much rain and snow does it fall in the West?
Rainfall totals are expected to range from 3 to 6 inches across southern Oregon, far northern California, the northern Sierra Nevada foothills and Washington’s Olympic Peninsula. Rainfall totals less than an inch are likely from the Bay Area to western Washington and Oregon.
Since this is the first stronger storm system of the season, no flooding is expected and precipitation will be largely beneficial. Subsequent storm systems may increase flooding risks, particularly near wildfire scars, where mudslides and debris flows become a greater threat.
It won’t be the craziest snowmaker in the Sierra Nevada, but snowfall totals of over 2 feet are possible by the end of the week.
Traveling through the Sierra will be very difficult with high snowfall rates and low visibility. Strong winds will further complicate plans. The sky will be clear during the day on Saturday.
The next storm will sweep much of the West Coast southward on Sunday.
(MORE: Why snow differs on slopes in the Rockies, Sierra and Northeast)
Where are the biggest waves on the West Coast?
There is also the element of massive waves, which are dangerous to coastal communities and beach erosion.
These storm systems could cause waves up to 15 to 25 feet, potentially breaking up to 35 feet at prime locations. The highest waves are likely from Northern California to the Oregon Coast.
By midweek, a smaller storm system could bring a renewed likelihood of increased waves.
The risk of rip currents and sneaker waves will be above average through early this week.
(MORE: When do major winter storms typically start in the United States?)
High tides combined with high water levels due to El Niño could create several feet of coastal flooding during each of these storms.
Coastal debris, including evergreen tree logs, could become projectiles in cresting waves during these storms. This debris has killed and seriously injured people on beaches in the past, according to the National Weather Service in Portland, Oregon.
(MORE: Super El Niño nears record strength)
Jonathan Belles has been a digital meteorologist since weather.com for 10 years. His favorite climate is tropical, but he also enjoys covering high-impact weather events, breaking news and winter storms. He is a two-time graduate of Florida State University and a proud graduate of St. Petersburg College.
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