Pacific Northwest Braces for Another Bomb Cyclone and Atmospheric River

Just as the West Coast is recovering from the Tuesday bomb cyclone, the region is set to see another one of these events by the end of the week. Here is a look at this highly volatile weather forecast for this part of the country.

Pair of Bomb Cyclones and Atmospheric Rivers Strike the Western U.S.

The highly active weather pattern is going to continue for the Pacific Northwest and down into California in the days ahead. Mother Nature is not letting up as the region experiences two bomb cyclones and a pair of atmospheric rivers in a period of just one week. The stormy weather will continue through the weekend along the coastline.

After taking the brunt of a bomb cyclone late Tuesday and into Wednesday, another one of these potent storms is forecast to strike the region late Thursday and into Friday. The silver lining is that this bomb cyclone is not predicted to be as powerful as Tuesday's storm. Instead, the late week cyclone will skirt past the coastline of Northern California, Oregon, and Washington without pushing far inland.

However, forecasters are warning that the potent weather maker will be close enough to usher in high winds, rain, and snow to some areas. A bomb cyclone is defined as a storm that intensifies so quickly that its central atmospheric pressure falls by 0.71 of an inch or greater in a time period of 24 hours or less. Tuesday's bomb cyclone saw its central pressure fall a massive 1.71 inches.

The winds from Tuesday's storm hit the Seattle area particularly hard. At least two fatalities were blamed on the storm in addition to over 600,000 customers being left without power. Crews are still working to restore power but energy providers are warning that it could be days before all the lights are back on throughout the region.

What to Expect with the Second Storm System

The upcoming bomb cyclone will produce the strongest winds along the coastline of Washington and northern Oregon. This differs from Tuesday's storm that was able to push into the populated Interstate 5 corridor.

An atmospheric river developed after the first bomb cyclone and that effect is predicted to happen again when the second cyclone whips up. The long plume of moisture coming in from the ocean will set their targets on the same general area as the week's first atmospheric river.

The heaviest rains will hit the area from Northern California up into the southwestern corner of Oregon. The most potent bands of rain will hit this area late Thursday and into Friday morning. Forecasters are also predicting that severe thunderstorms may fire up between the two atmospheric river events. These storms may pack instances of hail and gusty winds.

The rainfall from both events will hit totals of 8 to 12 inches in the zone from southern Oregon to Northern California. Widespread rainfall amounts of 1 to 4 inches is in the forecast up and down Interstate 5.

The back-to-back major rainfall events will create the threat of flash flooding, landslides, mudslides, and beach erosion for the coastal areas of Washington, Oregon, and Northern California.

A rare high-risk excessive rainfall outlook is now in place through Thursday night, levied by NOAA's Weather Prediction Center in northwest California. The largest city in this zone is Eureka.

Heading to the south, the areas north of the San Francisco Bay Area will get hit the hardest. For instance, the community of Santa Rosa is predicted to pick up 4 to 8 inches of rain while the metro area of San Jose may only see an inch. That said, the rain will be enough to slow down motorists on Friday throughout San Francisco, Sacramento, and San Jose.

Higher Snow Levels with Second Storm

Snow levels will be higher with the second of the duo of storms. The bulk of the snow that falls at the end of the week will come down above pass level, in contrast to the earlier snow event that saw the flakes fly at lower levels.

While this is good news for motorists, the melting will create runoff and potential flooding at intermediate elevations. Cumulative snowfall amounts for the week will range between 1 to 3 feet in the high country of the Siskiyous, the northern Sierra Nevada, and the Cascade Mountains.

The Pacific Northwest will have a short time to catch its breath after the late week bomb cyclone exits the region. However, a third storm system will be waiting on deck to come ashore from the Pacific Ocean at the end of the weekend. It is this storm that is likely to impact Southern California.

The Los Angeles metro area could pick up 0.50 of an inch to 1 inch of rain beginning Sunday and lasting through the day and into the overnight hours. Should this forecast prove to be true, it will be the first measurable rainfall for downtown Los Angeles since the middle of May.

San Diego is not expected to pick up as much rain. In addition, any rain that does fall this far south is likely to hold off until late Sunday or early Monday. The line of moisture is also predicted to make it over the Coast Ranges, remaining a primarily coastal event.

The active storm pattern is going to continue into the week of Thanksgiving for the western U.S. Travelers taking to the roads and skies will want to keep abreast of the potentially stormy weather and its associated travel disruptions in the week ahead.

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