A storm off the Northwest coast is being called a ‘bomb cyclone.’ What does that mean?

SPOKANE, Wash. — A major storm is approaching the Pacific Northwest and will be the main factor in kicking off several days of wet weather around the region.

This storm is being called a bomb cyclone– but what does that even mean?

If you haven’t heard of a bomb cyclone before, it’s not something that was used in common language until 2018. The origin and definition of what is or is not a bomb cyclone goes back to 1980.

So, what is a bomb cyclone anyway? Let’s start off by saying that a cyclone is a common term for a storm with an area of low pressure where winds spiral in towards it.  Hurricanes, for example, are tropical cyclones while high-pressure systems are called anticyclones in scientific circles. If we’re talking about low pressure, a storm, or a storm system, we’re usually talking about a cyclone.

describing what the requirements are for a bomb cyclone

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A bomb cyclone refers to the rapid drop in pressure in a strengthening storm

Let’s get to the bomb part now. Since the 1950s, meteorologists would nickname certain cyclones bombs because of how quickly they strengthened. A study in 1980 defined a weather bomb (also sometimes called bombogenesis) as when a storm’s pressure drops 24 millibars in 24 hours. A rapid drop in pressure means the storm becomes stronger, particularly when it comes to wind speeds. The Pacific Northwest is no stranger to severe wind storms, so it’s likely many of the dozens of them that impacted this region met the requirements to be a bomb cyclone.

comparing the cyclone forecast on Thursday with a category 1 hurricane

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While this weeks' bomb cyclone isn't quite at hurricane strength, many strong cyclones can be as strong as hurricanes.

That brings us to the storm heading towards the Northwest.

This storm will bomb out overnight and will be packing winds between 60 and 70 mph on Thursday as a result. These wind speeds are similar to a strong tropical storm, a few miles-per-hour below hurricane force.

Wind warnings are in place for coastal B.C. in Canada for these winds. Winds on the Washington and Oregon coasts are forecast to be much milder, 30 to 40 mph. In the Inland Northwest, the cyclone will bring us more wet weather starting on Friday. The windy core of the storm will keep heading north towards Alaska before fizzling out.

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