Water supply index forecast for January 1, 2015

DWR?s Frank Gehrke of California?s Snow Surveys performs snow survey with California Legislative fellows Toni Lee and Karen Morrison.From the Department of Water Resources:

NEW_DWR_LOGO_14inchA 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.

Next Update:

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.

Important Links:

Full Natural Flow Data:

Daily FNF: http://cdec.water.ca.gov/cgi-progs/snowsurvey_ro/FNF

Monthly FNF: http://cdec.water.ca.gov/cgi-progs/snowsurvey_ro/FNFSUM

Seasonal FNF: http://cdec.water.ca.gov/cgi-progs/snowsurvey_ro/FLOWOUT

Precipitation Data:

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


Snow Data:

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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