West Coast's 'Bomb Cyclone' Has Arrived

What was expected to be one of the strongest storms in the northwest US in decades arrived Tuesday evening, knocking out power and downing trees across the region, the AP reports. The Weather Prediction Center issued excessive rainfall risks beginning Tuesday and lasting through Friday as the strongest atmospheric river—a large plume of moisture—that California and the Pacific Northwest has seen this season bears down on the region. The storm system is considered a " bomb cyclone," which occurs when a cyclone intensifies rapidly.

• Hurricane-force winds, which are gusts above 75mph, could be felt along the Oregon coast, according to the National Weather Service in Medford, Oregon.
• Near Seattle, conditions for a "mountain wave" were shaping up, bringing large, low elevation wind gusts that could cause widespread power outages and downed trees, said Larry O'Neill, director of the Oregon Climate Service and Oregon State University associate professor. "This will be pretty strong in terms of the last 10 or 20 years," he said. "We've only seen a couple storms that have really been this strong."

• More than 106,000 customers had lost power in Washington as of Tuesday evening, according to poweroutage.us. More than 11,000 had lost power in Oregon and nearly 12,000 in California.
• The National Weather Service in Seattle said a peak wind speed of 68mph was recorded at Crystal Mountain near Mount Rainier. A wind speed of 53mph was also recorded at Ediz Hook, a 3-mile-long sand spit northwest of Seattle that extends from the northern shore of the Olympic Peninsula at Port Angeles into the Strait of Juan de Fuca. Winds were expected to increase in western Washington throughout the evening, the weather service said.
• In northern California, flood and high wind watches were in effect, with up to 8 inches 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, where 15 inches of snow was possible over two days. Wind gusts could top 75mph in mountain areas, forecasters said.
• "Numerous flash floods, hazardous travel, power outages and tree damage can be expected as the storm reaches max intensity" on Wednesday, the Weather Prediction Center warned.
• A blizzard warning was issued for the majority of the Cascades in Washington, including Mount Rainier National Park, starting Tuesday afternoon, with up to a foot of snow and wind gusts up to 60mph, according to the weather service in Seattle. Travel across passes could be difficult if not impossible.

(More atmospheric river stories.)