A Water Year 2015 Water Supply Index (WSI) forecast for conditions as of January 1, 2015 is posted at http://cdec.water.ca.gov/cgi-progs/iodir/WSI.2015.
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) 6.7(Below Normal) San Joaquin Valley Index (SJI)(75 percent exceedance) 1.4(Critical)
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:
Region October – December Runoff (%) December Runoff (%) Sacramento Valley Index (4 rivers) 114 161 San Joaquin Valley Index (6 rivers) 43 59 Tulare Lake basin (4 rivers) 33 37
Precipitation for the 2014-15 water year accumulated at the following rates of average:
Region/Index WY accumulated Precipitation through December 31, 2014 units= percent of average Sacramento River 131 San Joaquin River 95 Tulare Lake 88 Statewide 112 Northern Sierra 8-Station Index 129 (22.8 inches) San Joaquin 5-Station Index 70 (9.1 inches)
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):
Region Snow Water Equivalent (inches) % of Average (Apr. 1) % of Average (Jan 8) Northern 5.9 20 47 Central 4.8 16 38 Southern 4.1 15 39 Statewide 4.9 17 41
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.
Full Natural Flow Data:
Seasonal FNF: http://cdec.water.ca.gov/cgi-progs/snowsurvey_ro/FLOWOUT
Latest Northern Sierra 8-Station Precipitation Index: http://cdec.water.ca.gov/cgi-progs/queryDaily?s=8SI&d=today
Latest San Joaquin 5-Station Precipitation Index: http://cdec.water.ca.gov/cgi-progs/queryDaily?s=5SI&d=today
Latest Snow Sensor Report: http://cdec.water.ca.gov/cgi-progs/snow/PAGE6
Latest Statewide Summary of Snow Water Equivalents: http://cdec.water.ca.gov/cgi-progs/snow/DLYSWEQ
Extended Regional Forecasts:
California Nevada River Forecast Center 6 Day QPF and Snow Level Forecast: http://www.cnrfc.noaa.gov/awipsProducts/RNOHD6RSA.php
Climate Prediction Center One-Month Outlook Forecasts: http://www.cpc.noaa.gov/products/predictions/30day/
Climate Prediction Center Three-Month Outlook Forecasts: http://www.cpc.noaa.gov/products/predictions/long_range/seasonal.php?lead=1
U.S. Seasonal Drought Outlook: http://www.cpc.ncep.noaa.gov/products/expert_assessment/sdo_summary.html
Weather Forecast Office California Service Area-Products: http://www.cnrfc.noaa.gov/forecasts.php
El Nino Southern Oscillation (ENSO) Conditions and Weekly Discussion (including La Nina): http://www.cpc.ncep.noaa.gov/products/analysis_monitoring/lanina/enso_evolution-status-fcsts-web.pdf
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