PROJECT ALERT NOTICE (CA) Flooding in CA expected from AR storm causing rapid snowmelt

Date: Sat, 07 Apr 2018 13:19:16 EDT

Summary: Runoff from heavy rainfall and rapid snowmelt is predicted to cause at least 20 rivers in CA to rise above flood stage today and tomorrow.

Yesterday a warm atmospheric river (AR) storm brought 4-5 inches of precipitation to the north coast and to parts of the Sierra Nevada. Today, the storm moves out of the region, but not before bringing another 1-2 inches of precipitation to the Sierra Nevada. Runoff from heavy rainfall and rapid snowmelt has caused many rivers in CA to rise, with peakflows expected today and tomorrow. The Sierra Nevada and its foothills are under flood watch through Sunday. Yosemite Valley is closed through Sunday in anticipation of moderate-to-major flooding expected; streamflow is predicted to be nearly 5 feet above flood stage at a USGS gage located in Yosemite Valley (11266500, Merced River at Pohono Bridge). A USGS webcam for the USGS streamgage located within Yosemite National Park can be accessed at: https://ca.water.usgs.gov/webcams/happyisles/

The National Weather Service predicts streamflow at 15 flood forecast points in California will exceed monitor stage, and another 5 will exceed flood stage. USGS WaterWatch reports that streamflow at about 4 USGS gages in California could experience peak-of-record flows, including one gage located in the foothills, Big Creek (11284400), with 48 years of record. Currently, 18% of USGS streamgages in CA have flows above the 90th percentile for this day of year, with 7 streamgages experiencing highest flows ever for this date.

Today, the USGS California Water Science Center (CAWSC) currently has 9 crews deployed for flood response from the following service areas: Redding, CA (2 crews); Ukiah, CA (3 crews); Truckee, CA (2 crews), and Sacramento (2 crew). No crews are expected to deploy tomorrow, but USGS management will continue to assess the situation as streams respond to runoff. Currently, all streamgages are transmitting data. No equipment damage or safety issues have been reported.