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Bomb cyclone and atmospheric river will impact the Pacific Northwest: What you need to know

By Kelley Bayern,


PORTLAND, Ore. ( KOIN ) — As we slide into the fall season this weekend , our weather pattern across the Pacific Northwest will follow suit with cooler temps and a healthy dose of rainfall by early next week, with weather models showing an active weather pattern setting up with a train of storm systems arriving into the region.

One of these storms could be a doozy and classified as a “bomb cyclone,” bringing heavy rainfall, flooding concerns, and high winds to portions of the state.

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You may have heard the term “bomb cyclone” in your news feed recently because it has become a popular weather word over the last five or so years. But “bomb” is such a touchy word and now we’re throwing it around casually into conversations about rain? Sheesh! My goal here is to define a bomb cyclone and its differences from typical storms we see in the fall and winter, and to inform you of any impacts we may see as this one inches closer over the weekend.

What is a bomb cyclone?

First of all, bomb cyclones are a very real thing. On occasion, storms developing far out over the ocean can undergo bombogenesis, or “bomb out” for short, when their central pressure drops 24 millibars within 24 hours. Due to the rapid drop in pressure, very strong winds and rain can form within these storms. They are often the culprit of our damaging wind storms around the region, too. Bomb cyclones can also form in both the Pacific and Atlantic basins during the stormy season.

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There’s a good chance that Sunday’s storm “bombs out.”
Bomb Cyclone on January 5th, 2023

How do bomb cyclones differ from typical storms?

Well, both are storms. One is just more powerful.

Here’s an easy way to picture things. Imagine two cars parked side by side. One of them is a normal sedan; maybe a Honda Civic. The other is a Lamborghini. Both of them are cars. Both have wheels and a steering wheel and perform the same driving function. But one of them is much faster and more powerful and could smoke the other in a street race. A bomb cyclone is basically the Lamborghini of storms. It’s bigger, more powerful, and also prettier from a satellite view, too.

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We have seen bomb cyclones recently around the region. There was one earlier this year on January 5th that brought high winds and heavy rainfall to northern California and southern Oregon. The large storm’s high winds knocked out power across the Rogue Valley. The storm stayed just offshore enough to not impact the Portland metro area.

Impacts this weekend

Thankfully, the center of this bomb cyclone will be far out and over the open ocean; otherwise, we’d be in for a damaging wind storm. However, the region will still feel impacts from this system’s outer rain bands fueled by a moderately strong atmospheric river.

The highest rain amounts are forecast to hit the southern Oregon coastline with 2″+ of rainfall. These counties include Curry, Douglas, and Josephine counties. The higher elevations of the Coast Range could also see closer to 3″+ of rain, which brings concerns for flash flooding over burn scars from recent fires, including the Tyee Ridge Complex, the Anvil Fire, and the Flat Fire.

Winds will also turn the strongest along the southern coastline with gusts nearing 50 mph by Sunday night in Coos and Curry counties. Wind gusts may reach high speeds over some of the headlands. The central and northern coastlines may see gusts up to 30+ mph over the weekend.

Impacts in Portland will include widespread rainfall that could be heavy at times, starting anytime Sunday night to Monday morning. Forecasts bring rain amounts of 0.3″ to 0.6″ to the valley just on Monday alone. Thunderstorms could also play a role early next week with the occasional downpour or rain and hail.
Forecast Rain Totals in Portland on Monday

Drivers, be ready for rainy commutes both in the morning and evening time. You should use caution and give yourself extra time to navigate around as we all adjust to driving in the rain again.

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So don’t be alarmed as this bomb cyclone cruises by the region. We can all handle a rainy day once in a while, we’re Oregonians after all! And the next time you hear the term “bomb cyclone,” just imagine a Lamborghini driving by. It’s only scary if it’s roaring down the road right at you. And this time, our Lambo is parking itself at the shop next door.

Copyright 2023 Nexstar Media Inc. All rights reserved. This material may not be published, broadcast, rewritten, or redistributed.

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