The parade of Pacific storms is moving southward, focusing on much of California beginning during the Christmas week. Heavy rains will cause floods as snow accumulates in the Sierra Nevada.
The storm train, including a pineapple express centered on western Washington, will turn southward this weekend and focus on California for most of the Christmas week. As the rain falls more frequently, the risk of flooding and mudslides increases.
Pineapple express to visit Northern California starting this weekend
“The upcoming atmospheric river that will focus on Northern California from late Saturday night to Monday qualifies as a pineapple express,” AccuWeather Senior Meteorologist Brett Anderson explained.
A pineapple express is an atmospheric river, or plume of moisture, that runs from near Hawaii to the United States’ West Coast.
The forecasted heavy rain will come after a storm that will bring heavy rain and flooding to western Oregon to end the week. Some of the storm’s rain will fall in Northern California until Friday night.
The storm will bring 4–8 inches of rain to the northwestern region of California by the end of the week, with 0.50 inches in the Sacramento Valley and 4 inches in the Siskiyous and northern Sierra Nevada.
“The storm from Saturday night to Monday will bring more substantial rain to Northern California,” AccuWeather Lead Storm Warning Meteorologist Michael Stahlman stated.
From Sunday to Monday, the west-facing slopes of the Coast Ranges, Siskiyous, and northern Sierra Nevada might receive several inches of rain in a few hours at the peak of the atmospheric river.
“Pockets of 6-12 inches are forecast, especially in the lower and intermediate west-facing slopes of the northern Sierra Nevada,” according to Stahlman. That quantity of rain in 12-48 hours is more than enough to cause rapid minor stream and short-run river flooding.
San Francisco’s rainfall is expected to be between 2 and 4 inches. Ponding in low-lying places will cause roads to become slick. Where leaves clog storm drains, more severe urban flooding is likely to occur.
New Pacific storm to form Christmas week, reach much of California
The atmospheric river is expected to subside from Monday to Monday night while a new storm forms just off the West Coast of the United States in the middle of next week.
Rain will become more widespread across much of California during the Christmas week.
“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,” said Julia Williams, an AccuWeather Storm Warning meteorologist.
Rain may begin in coastal Southern California as early as Tuesday.
Drenching downpours and urban floods are expected to occur in the Los Angeles and San Diego metro areas from Wednesday to Friday, potentially disrupting outdoor Christmas activities. These places are likely to receive some rainfall on Christmas Day. Some showers will reach the California deserts from far inland. Showers may reach as far as Las Vegas and Phoenix.
“As the rain expands into the southern part of California, there is a medium to high risk of flooding, especially in the south- and west-facing slopes of the Transverse Mountains in the region from Tuesday to Thursday,” Williams told reporters.
Meanwhile, western Washington and Oregon will have less rain and snow than recently. However, these places will likely get some rain or mountain snowfall during the Christmas week.
Sierra Nevada snow upcoming
Snow levels will be high this weekend, but will fluctuate across the Sierra Nevada during the Christmas week. Several feet of snow are forecast on the Sierra Nevada’s ridges and peaks, which will be a godsend for ski enthusiasts over the holidays and a future boost for runoff in the spring and early summer, as little to no snow has fallen thus far this season.
Snow will occasionally fall on Interstate 80 near Donner Pass, California, making traffic hazardous. Motorists are recommended to check the local AccuWeather prediction on a regular basis for information on when the most significant snowfall will occur in the region.
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