CW3E AR Update: 28 February 2017 Post Event Summary and Outlook

February 28, 2017

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Summary of the ARs that impacted the U.S. West Coast over the past week

• Landfalling AR brought weak-to-moderate AR conditions to portions of Southern CA for ~24 hours between 27 and 28 February
• >6 inches of precipitation fell over the high elevations of San Diego County with lower elevations receiving 1.5–4 in.
• The San Diego River rose to ~14.15 feet at 2 am 28 Feb, 2.8 feet above flood stage, and the 3rd highest peak all time
• The heavy precipitation led to several road closures, multiple mudslides, hotel evacuations, and flooded businesses

Three ARs expected to make landfall over the U.S. West Coast over the next ten days

• The first AR is expected to make landfall over the Pac NW ~1800 UTC 2 March 2017 with weak strength (IVT=250–500 kg m-1s-1). Weak AR conditions may propagate over N CA. prior to dissipation.
• A second AR is expected to make landfall over N CA. at ~0000 UTC 5 March 2017. Coastal areas of N CA may see several hours of moderate strength AR conditions.
• Long range forecasts indicate the potential for a third weak AR during 8-10 March 2017, however there is large uncertainty in the models beyond forecast day 5.
• Large scale pattern beyond forecast day 9 indicates the potential for a return to active AR landfall conditions over the Pac NW
  Highest precipitation and impacts from these events is predicted to be over the Olympic and Cascade Mtns. in WA and Coastal Mtns. In NW CA.

Click IVT or IWV image to see loop of 0-180 hour GFS forecasts Valid 0600 UTC 28 Feb – 1800 UTC 7 Mar 2017

Summary provided by C. Hecht, B. Kawzenuk, and F.M. Ralph; 1 PM PT Tues 28 Feb. 2017