Zooming Around with Zoe: Why bomb cyclones were able to bring historic rainfall to the Pacific Northwest

Zooming Around With Zoe

GREENVILLE, N.C. (WNCT) — One of the strongest extratropical cyclones ever recorded hit the West Coast of the United States in late October.

Sacramento, Calif., went from their longest dry spell to their rainiest day ever recorded.

Two intense storms hit the North Pacific in only a week, both with the classification of bomb cyclone. But they didn’t contain bombs; it just means the system had explosive development with pressure dropping more than 24 millibars in 24 hours. 

The bomb cyclones created what is known as an atmospheric river, dragging long narrow bands of moisture from Hawaii to the western United States.  The Center for Western Weather and Water Extremes ranked the October 24-25 event as a category 5 out of 5 for Northern California. Ocean swells of 16-24 feet were observed up and down the West Coast.  

Torrential rainfall soaked wildfires and brought a bit of relief from the extreme drought in the West. However, the land was not prepared to absorb all this water, which led to flash flooding, mudslides and power outages. In California alone, 7.6 trillion gallons of water fell in just three days…that’s about enough for 244 million people to use for an entire year! 

The NWS reported that Mount Tamalpais received a two-day rainfall total of 16.55 inches.  Blue Canyon, Calif., received over 10 inches of rain in less than a day.  Downtown San Francisco saw it’s wettest October day ever recorded. 

From extreme drought to extreme rainfall, this is just one of the many examples of how quickly the weather can change. It’s always important to remain weather aware. 

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