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Bomb Cyclone Click to start then Scroll Down

The headlines are filled with dramatic talk of the "Bomb" cyclone hitting the West Coast. When you have a large segment of the population traveling to "grandma's house", this makes for great news copy but is it accurate and does it mean destruction? Let's take a look at where this storm formed and see if we should call it a "BOMB!"

September 2019 Sea Surface Temperature Anomalies. (Red indicates warm water.)

We have seen unusually warm ocean waters sitting off the coast of California this year (area of red/orange in graphic above). This resulted in an unusually large number of days of eddy winds for San Francisco. Eddies are counter clockwise wind patterns that do not extend up very high in the atmosphere and are cut off from the major flow. We can likely blame these eddies on the blob of very warm ocean temperatures. Frequently we watched as an area of Low pressure formed in this region and then drifted off the coast, forming large eddies that brought Southerly winds into San Francisco.

November 2019 Sea Surface Temperature Anomalies

Fast forward to November and that blob of super warm water is still in the Eastern Pacific, though it has shifted a little to the west. Well, these warm waters are now providing one of the ingredients for our "Bomb" cyclone.

850 mb Temperatures. (California is highlighted)

Bomb cyclone is a term used when a Low pressure deepens very quickly, about 1 millibar per hour. We see this type of quick intensification when there is a large temperature contrast between two airmasses that are wrapping around a Low. On Monday a wave of cold air (seen above as area of blue) slid across the Eastern Pacific,over that blob and met up with the warm Pacific air. As they met the Low deepened very quickly.

Pressure Reading for Buoy, 500 miles west of Eureka, California

The Low sat over the Eastern Pacific on Monday and rapidly intensified - hence the term "bomb". This buoy (#46006) showed a drop of 0.45" inches of mercury or about 15mb. That is fast but not quite enough to be considered a bomb.

However a few hundred miles further west another buoy captured a drop of about 22 mb in 24 hours. The rapid drop in pressure qualifies this to be a termed a "Bomb Cyclone".
LGRC1 station located in hills to the east of Carpinteria, CA

The strong temperature and pressure gradients have translated into some powerful winds. As the Low and the trailing cold front have moved into California, sensors have picked up some localized blasts (as seen in the wind graphic above). Winds hit near 60 knots east of Carpinteria as the flow was funneled through the mountains.

The mottled clouds that appear in this visible satellite picture off the West Coast indicate cold air that is being driven south behind the cold front that is moving through Nevada and Southern California.

This cold weather will continue for awhile for the Southwest. Computer forecast models show a series of Lows this weekend moving over the Pacific, strengthening in this same region, and then sliding through California, bringing periods of rain, low elevation snow and gusty cold winds.

Created By
Kerry Anderson
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