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Overview - Historic flooding at Guerneville and Monte Rio

Atmospheric Rivers (ARs) are nothing new for the West Coast, especially California.  ARs can bring beneficial precipitation to the Golden State by adding much needed water to reservoirs and snowpack to the Sierra.  On the other hand, the tremendous amount of moisture associated with ARs can bring extremely hazardous weather, which is usually excessive rain and associated flooding. The events that unfolded on February 25 to February 27 fall in the hazardous category with a stalling AR and devastating flooding.

A low pressure began to take shape over the Eastern Pacific on February 25 as a decent moisture plume made landfall over Northern California. Over the next 24 hours the low pressure system moved eastward toward the coast and began to interact with the moisture plume. The interaction between the approaching low and moisture plume enhanced moisture transport across the Bay Area, especially Monterey Bay northward. Ultimately the moisture plume stalled across the North Bay bringing periods of moderate to heavy rain for time period of approximately 36 hours. 

The persistent moderate to heavy rainfall led to a three day total of 10 to 15 inches of rain across the Russian River watershed. The famously wet reporting station Venado recorded 21.56 inches of rain.  The impressive rainfall fell on top of already saturated soils, which severely limited water absorption into the ground. Numerous flood advisories and warnings were issued across the North Bay. Of greatest significance was the Russian River, which rose above flood stage on February 26 then continued into major flood stage the morning of February 27. The final crest near Guerneville occurred late on the evening of February 27.  River levels finally dropped below flood stage at Guerneville on the morning of March 1. The towns of Guerneville and Monte Rio were impacted the most with approximately 2,000 properties having some flood damage. At one point the town of Guerneville was completely cutoff and became an “island” only accessible by boat.

In addition to the notable flooding the passing cold front brought a round of very gusty winds toppling many trees across the Bay Area.  The highest wind gust recorded was 87 mph  on Big Rock Ridge.

Our colleagues at Center for Western Weather and Water Extreme also composed a technical and well written post event summary.  http://cw3e.ucsd.edu/cw3e-ar-update-25-27-february-post-event-summary/

 

Composed by: MMehle

Mill Street flooding in Guerneville

Mill Street flooding in Guerneville
Picture by Kent Porter @kentphotos

House flooded in Guerneville

House flooded in Guerneville
Picture by Karl Mondon @karklmondon

Flooding near Point Reyes

Flooding near Point Reyes
Picture by Ryan Walbrun @chileconsin

Satellite derived Total Precipitable Water

Satellite derived Total Precipitable Water

 

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