This WSI forecast is based on the precipitation and flows through December 2014 and can be summarized as follows:
Sacramento River Unimpaired Runoff Water Year Forecast(50 percent exceedance)
17.1 MAF(94 percent of average)
Sacramento Valley Index (SVI)(50 percent exceedance)
San Joaquin Valley Index (SJI)(75 percent exceedance)
Despite well above average precipitation and runoff for December in the Sacramento River Region, the SVI classification is Below Normal (much closer to Dry than Above Normal). This is due to the fact that the calculation of the index requires that the previous year’s index value (4.1) be weighted 30 percent.
Unimpaired flows for the 2014-15 water year have run at the following rates of average:
October – December Runoff (%)
December Runoff (%)
Sacramento Valley Index (4 rivers)
San Joaquin Valley Index (6 rivers)
Tulare Lake basin (4 rivers)
Precipitation for the 2014-15 water year accumulated at the following rates of average:
WY accumulated Precipitation through December 31, 2014 units= percent of average
The precipitation events in December were Atmospheric River (AR) events. The moisture plume associated with an AR has very definitive boundaries. Consequently, the amounts of precipitation can vary significantly over a short distance (one or two basins). The AR of December did not extend into the San Joaquin Region.
The snowpack as of the morning of January 8 stands at the following (based on snow sensors):
Snow Water Equivalent (inches)
% of Average (Apr. 1)
% of Average (Jan 8)
Weather and Climate Outlooks:
The 6-day weather forecast indicates no precipitation anywhere in the Sierra. The freezing levels over the entire Sierra are expected to be near 12,000 feet on Wednesday. The lowest elevations are expected Sunday when the freezing levels are forecast to be near 7,500 feet over the northern range and 8,500 over the southern range.
The NWS Climate Prediction Center (CPC) one-month outlook for January, issued December 31, indicates increased chances of above normal precipitation for the southern half of the state and, elsewhere, equal chances of above or below normal precipitation are expected. Temperatures are expected to be above normal for the entire state.
The CPC three-month (January-February-March) outlook, issued December 30, indicates increased chances of above normal precipitation and temperatures for the entire state.
ENSO-neutral conditions continue. Positive equatorial sea surface temperature anomalies continue across the Pacific Ocean. There is approximately a 65 percent chance that El Niño conditions will be present during the Northern Hemisphere winter and last into the Northern Hemisphere spring 2015.
The next WSI forecast and the first Bulletin 120 forecast for conditions as of February 1 should be available on February 9, 2015. If you have any questions regarding this forecast, please contact a member of the Snow Surveys staff.