STATE OF WASHINGTON — There is a so-called ‘bomb cyclone’ on its way to the northwest on Tuesday, but what does that mean? You’ve no doubt heard the term on the internet in recent days, as it started trending on social media over the weekend.
A ‘bomb cyclone’ is nothing new; we have been documenting the passage of similar storms here for decades. The term, referring to “an area of low pressure that drops at least 24 millibars within 24 hours,” was originally used in an academic article and presentation in the 1970s. However, it became part of the common lexicon after being hash-tagged on Twitter and Facebook in recent years.
Chief meteorologist Shannon O’Donnell calls terms like polar vortices, heat domes and bomb cyclones the “avocado toast of the weather world.” In other words, they were always a thing, but a few selfies and a trending hashtag later, and suddenly they’re a THING!
Nevertheless, a bomb cyclone is on the PNW doorstep tomorrow. This small area of low pressure will be just a blip on the map as of Monday evening, but on Tuesday it will quickly intensify into a very deep low pressure area over the Pacific Ocean and then approach the Washington coastline on Tuesday afternoon.
Keep in mind that areas of low pressure act like giant vacuum cleaners in the sky, sucking in air as quickly as possible. The deeper the low, the stronger the pull, building into a very impressive 949 millibar storm off the coast by Tuesday afternoon. A low this deep will draw air in at 25 to 60 miles per hour or more, so those of you along the coastline will experience easterly gusts of that magnitude. On some coastal headlands, wind gusts can exceed 120 km per hour.
Much of Puget Sound will be grateful to the Olympics for blocking most of the wind near the I-5 corridor, but communities near the Cascade foothills won’t be so lucky. That’s because easterly winds will howl across the passes as the storm approaches Tuesday.
Air flowing over the passes zigzags through the holes in the terrain and picks up speed through the tight spaces à la the Bernoulli effect. If that air reaches the bottom of the hills and has the freedom to spread, it will… with wind gusts expected to max out between 25 and 65 mph in foothill communities like North Bend, Maple Valley, Enumclaw and Sultan.
A high wind warning is in effect for both the Washington coast and the eastern Puget Sound lowlands, as the eastern side of Pierce, King and Snohomish counties are likely to experience the worst of the winds. Such gusts in the east are called “Cascadia winds,” and if they blow this extreme, widespread tree damage and power outages are likely.
For those closer to the coastline in Puget Sound, a lighter wind advisory is in effect, although southeasterly winds in places like Federal Way or Edmonds can still reach a top speed between 25 and 50 miles per hour.
Up in the mountains, howling winds and incoming precipitation will combine to create whiteout conditions due to heavy, blowing snow. As such, a rare blizzard warning has been issued above 2,000′ in the Cascades on Tuesday and Wednesday. Pass travel will be difficult to dangerous at times over the next 48 hours.
Those in the foothills below will be concerned not only about the wind, but another round of rain. Precipitation will increase again Tuesday afternoon through Wednesday as the frontal system accompanying this deep “bomb cyclone” moves through the region. Highs won’t top out until the 40s, so it will be a cold and gusty rain!
Last but not least, the coast will also be buffeted by large, dangerous surf. Sneaker waves are likely near the beaches of Washington and Oregon, so it’s best to view this upcoming atmospheric event from a safe distance from the coastline.
Skies are expected to ease later this week, although it will still look humid heading into the weekend.
