‘Bomb Cyclone’: Northern California, Pacific Northwest Atmospheric River Support

SEATTLE (AP) – Northern California and the Pacific Northwest are bracing for what is expected to be a powerful storm, with heavy rain and winds that will hit the region and potentially cause power outages and flash flooding.

The Weather Prediction Center issued an excessive rainfall risk starting Tuesday and lasting through Friday as the strongest atmospheric river — long feathers of moisture stretching far across the Pacific Ocean — which California and the Pacific Northwest have seen this season affect the region. The storm system has intensified so quickly that it is considered a ” bomb cyclone” explained Richard Bann, a meteorologist with the National Weather Service Weather Prediction Center.

The areas that could see particularly heavy rainfall as the large water plume moves landward are likely to stretch from the southern part of Portland, Oregon, to the northern part of the San Francisco area, he explained.

“Be aware of the risk of flooding at lower elevations and winter storms at higher elevations. It’s going to be a big event,” he said.

In Northern California, flooding and strong winds will take effect Tuesday, with up to 8 inches (20 centimeters) of rain predicted for parts of the San Francisco Bay Area, North Coast and Sacramento Valley.

A winter storm watch was issued for the northern Sierra Nevada above 3,500 feet (1,066 meters), where 15 inches (28 centimeters) of snow was possible over two days. Gusts could top 75 mph (120 km/h) in mountainous areas, forecasters said.

“Numerous flooding, hazardous travel, power outages and tree damage can be expected as the storm reaches maximum intensity” on Wednesday, the Weather Prediction Center warned.

Meanwhile, Southern California will see mid-dry conditions this week gale force Santa Ana winds which could increase the risk of wildfires in areas where crews are still soaking up a large fire that destroyed 240 structures. The Mountain firewhich erupted Nov. 6 in Ventura County northwest of Los Angeles, was about 98% contained Monday.

Winds will ease by the end of the week with a chance of rain in the Los Angeles area.

In southwestern Oregon near the coast, 4 to 7 inches (10 to 18 centimeters) of rain — with as much as 10 inches (25 centimeters) possible in some areas — is forecast for late Thursday night and early Friday morning, Bann said.

A high wind warning has been issued for the northern and central Oregon coast beginning at 4 p.m. Tuesday with southerly winds 25 mph (40 km/h) to 40 mph (64 km/h), gusting to 60 mph ( 97 km/h) expected, according to the weather service in Portland. Wind gusts up to 70 mph (113 km/h) are possible on beaches and headlands. Widespread power outages are expected with winds that can topple trees and power lines, the weather service says. Travel is also expected to be difficult.

Washington could also see heavy rainfall, but probably not as bad as Oregon and California. From Monday night into Tuesday, some of its coastal areas could receive as much as 1 inch (3.8 cm) of rain, Bann said.

The weather service warned of strong winds from Tuesday afternoon into early Wednesday for coastal parts of Pacific County in southwest Washington. With gusts potentially topping 35 mph (46 km/h) — and likely faster near beaches and headlands — trees and power lines are at risk of being toppled, the Pacific County Emergency Management Agency warned.

Washington State Patrol Trooper John Dattilo, a patrol spokesman based in Tacoma, posted on social media Monday afternoon that people should be prepared for “some inclement weather” Tuesday night. “Stay off the roads if you can!”

A blizzard warning was issued for most of the Cascades in Washington, including Mount Rainier National Park, as of Tuesday afternoon with up to a foot of snow and wind gusts up to 60 mph (97 km/h), according to the weather service in Seattle. Traveling across passes can be difficult, if not impossible.

Outside of that region, the central and eastern Gulf Coast, including the Florida Panhandle, is at risk of flooding Tuesday, with 2 to 3 inches (5 to 7.6 centimeters) of rain in the forecast, according to the weather service. Low-lying and urban areas can experience flash flooding.

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Weber reported from Los Angeles. Associated Press reporter Lisa Baumann contributed to this report.