Heavy rain, flooding from Pacific storms to focus on California leading up to Christmas
The parade of Pacific storms is on the move and will focus farther south over much of California beginning during the week of Christmas. Rounds of heavy rain will lead to flooding as snow piles up in the Sierra Nevada.
In today’s Forecast Feed, Bernie breaks down what the weather looks like in the coming days in the United States.
The train of storms, including a Pineapple Express that has focused on western Washington, will shift south this weekend to concentrate on California through much of the week of Christmas. As the rounds of rain intensify, so will the risk of flooding and landslides.
Pineapple Express to visit Northern California starting this weekend
"The upcoming atmospheric river that will focus on Northern California from late Saturday night to the early week qualifies as a Pineapple Express," AccuWeather Senior Meteorologist Brett Anderson said.
A Pineapple Express is a specific atmospheric river, or plume of moisture, that extends from near Hawaii to the West Coast of the United States.
"The storm from Saturday night to Monday will bring more substantial rain to Northern California," AccuWeather Lead Storm Warning Meteorologist Michael Stahlman said.
There is the potential for several inches of rain to fall in a few hours at the height of the atmospheric river from Sunday to Monday alone in the west-facing slopes of the coastal ranges, Siskiyous and northern Sierra Nevada.
"Pockets of 6-12 inches are likely, especially in the lower and intermediate west-facing slopes of the northern Sierra Nevada," Stahlman said.
That amount of rain in a span of 12-48 hours is more than enough to unleash rapid small stream and short-run river flooding.
Additional rain will fall across much of Northern California from Tuesday to Wednesday.
San Francisco's rainfall is projected to range from 2-4 inches during the atmospheric river through the first part of Christmas week. Roads will become slick with ponding in low-lying areas. Where leaves block storm drains, more significant urban flooding is likely to occur. Rocks and mud will block some roads. Hillside and streamside roads may be prone to erosion and landslides, which can cause them to wash out.
Strong winds will accompany the storm into the first part of the week. Gusts approaching hurricane force, 74 mph, are most likely over some of the ridges and mountain passes, as well as some of the high ground right along the coast.
New Pacific storm to impact California Christmas week
The atmospheric river is forecast to abate from Monday through Monday night as a new storm develops just off the U.S. West Coast in the middle of this week.
Rain will become more widespread across much of California during the week of Christmas.
"Due in part to the atmospheric river at the start of the week, additional rain from Tuesday to Thursday in parts of Northern California, particularly in the west- and southwest-facing slopes of the mountains, will lead to a medium to high risk of flooding," AccuWeather Storm Warning Meteorologist Julia Williams said.
Rain may begin in parts of coastal Southern California as early as Tuesday.
Drenching downpours and urban flooding are forecast for the Los Angeles and San Diego metro areas from Wednesday to Friday, which may disrupt outdoor Christmas-related activities. At least some rain is expected in these areas on Christmas Day. Some showers will reach the California deserts well inland. Showers may extend as far inland as Las Vegas and Phoenix.
The heaviest rainfall totals are expected across the San Gabriel Mountains and portions of the Sierra Nevada from Tuesday night to Thursday night. The Los Angeles basin and surrounding areas will receive 2-4 inches of rain during the same period.
The average monthly rainfall for the city itself for the entire month of December typically ranges under 2.5 inches, for reference.
Meanwhile, in western Washington and Oregon, the weather will be less rainy and snowy than in recent weeks. However, it is unlikely that the week of Christmas will be totally free of rain and mountain snow in these areas.
Sierra Nevada snow upcoming
Snow levels will start off high this weekend through the early week, but will fluctuate in the Sierra Nevada through the week of Christmas.
"Ten to 12 feet of snow are expected on the ridges and peaks of the Sierra Nevada through the week of Christmas," AccuWeather Chief On-Air Meteorologist Bernie Rayno said.
The snow will be a boon for ski enthusiasts over the holidays and a future boost for runoff during the spring and early summer, as little to no snow has fallen thus far this season.
However, snow will periodically dip down to Donner Pass, California, along Interstate 80, and that will pose difficulties for travel. Motorists are encouraged to check the local AccuWeather forecast daily for updates on when the most intense snow will fall in the region.
Want next-level safety, ad-free? Unlock advanced, hyperlocal severe weather alerts when you subscribe to Premium+ on the AccuWeather app. AccuWeather Alerts™ are prompted by our expert meteorologists who monitor and analyze dangerous weather risks 24/7 to keep you and your family safer.
Report a Typo
