The Far West
A steady stream of Pacific fronts brought precipitation to parts of the Far West every day this USDM week. The precipitation fell as rain at the lower elevations, with 1 to 2 feet of new snow measured at the higher-elevation SNOTEL sites in the Cascades and parts of the Sierra Nevada. Mountain snowpack was near to above average at most of the high elevation SNOTEL sites across the Far West. Ten inches or more of precipitation occurred in favored upslope areas of northern California to Washington, with 2 inches or more from central California to Washington. Precipitation amounts dropped off to the lee of the mountains and in Southern California, with essentially no precipitation falling along the California-Arizona border. This week’s precipitation, coupled with last week’s, totaled over 20 inches in the favored upslope locations. While it improved mountain snowpack and reservoir levels, significant precipitation deficits remained across California from the state’s 4 to 5 year drought.
D1-D4 were pulled back in northern to central California and along the coast based on several criteria. Improvements were made where 6-month precipitation deficits were erased and reservoir levels were restored to average for this date. As of March 14, near-average reservoirs included Shasta Reservoir (106% of average), Folsom Lake (120%), and Lake Oroville (101%). Napa County reservoirs are all full, apart from Berryessa. But most of the other California Department of Water Resources (DWR) reservoirs were still below-average, including Trinity Lake in the north (at 60% of average). The surface soils were saturated due to the recent rains, but the deeper groundwater levels had not recovered. Wells were still going dry in Tuolumne County and deficits continued in groundwater and reservoir levels supplying areas such as San Joaquin County. DWR March 14 statistics showed mountain snowpack snow water content (SWE) at 100% of the April 1 average in the Northern region, 90% in the Central region, and 77% in the Southern region. With a near to below-normal mountain snowpack, streamflow is expected to be near to below normal during this summer at current projections.
Source: Richard Heim, NOAA/NCEI, US Drought Monitor, March 15, 2016