The first big blow of the season struck the Pacific Northwest less than two weeks ago, driving extreme rains and intense winds.
It was caused by a weather phenomenon known as a bomb cyclone, a rapidly strengthening storm fueled by a steep and sudden drop in atmospheric pressure.
This pattern developed over the Pacific Ocean during the last week of October. When the system made its way onshore, its strongest impact was felt on Oct. 24 along the Washington and Oregon coasts and in Northern California. Some areas received record-setting rainfall and wind gusts up to 85 mph – above hurricane force which starts at 74 mph.
As the storm fizzled its way over the Cascade Range and into the Inland Northwest, we still felt some of its zeal with wind gusts up to 45 mph and more rainfall in a single day than we saw in July and August combined.
Coincidentally, 48 hours later, a bomb cyclone that formed over the Atlantic Ocean slammed into the Northeast, pummeling the region with excessive rains and powerful winds. Though not related, the two storm systems – one over the Atlantic, the other above the Pacific – originated when a mass of warm air collided with a mass of cold air, generating a nontropical cyclonic effect. This pinwheeling pattern led to plunging atmospheric pressure, which, in turn, rapidly intensified the storm as it sucked more air into its circulation.
When these cyclonic, low-pressure storms develop off the East Coast, they’re called Nor’easters. Why, then, aren’t the storms that form off the West Coast called Nor’westers? The answer is blowing in the wind.
Many people think those storms are called Nor’easters because they strike the northeastern states. And while they do mostly impact that region, the name is actually derived from the storms’ strong northeasterly winds.
By contrast, a bomb cyclone forming off the Washington coast can be fed by a variety of wind directions, or a primary wind direction may shift as it heads toward land. And so, a name based on northwesterly winds would not be accurate.
Nor’easters make far bigger news than our cyclonic storms because they hit more densely populated areas than along the coastal Pacific Northwest and Northern California. The most congested coastal corridor in the U.S. includes New York City, Boston, Philadelphia, Baltimore and Washington, D.C., all of which get impacted.
Which isn’t to say that bomb cyclones generated in the North Pacific cause little damage to our region. We’ve had some whoppers over the years, especially the historic Oct. 12, 1962, Columbus Day Storm – the most violent weather event to strike the Pacific Northwest in the 20th century. It bore down on Washington, Oregon and Vancouver, British Columbia, unleashing torrential rains and wind gusts up to 100 mph that killed 46 people and destroyed thousands of homes and businesses.
Bomb cyclones can occur at any time of year, but are most common during the colder months of October through March. That said, it’s possible we’ll see another cyclone form somewhere off the West Coast before Easter. It may never make landfall here in Washington state. But if it does, moisture could fall as heavy snow in areas with freezing temperatures. Maybe even here in the Inland Northwest.
Which wouldn’t necessarily be a bad thing. A big snow dump would help raise reservoir levels left low by our region’s historic drought. And after the winds abate, residents could head outdoors to dig out the sleds, hit the slopes or strap on the snowshoes.
Nic Loyd is a meteorologist in Washington state. Linda Weiford is a writer in Moscow, Idaho, who’s also a weather geek. Contact: email@example.com
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