WATER SUPPLY INDEX for January 1, 2019

Photo by DWR

From the Department of Water Resources:

Forecast Summary:

A Water Year 2019 Water Supply Index (WSI) forecast for conditions as of January 1, 2019 is posted at http://cdec.water.ca.gov/reportapp/javareports?name=WSI. The WSI forecast is based on the precipitation and runoff (full natural flow) through December 2018 and can be summarized as follows:

Sacramento River Unimpaired Runoff Water Year Forecast

(50 percent exceedance)

 14.0 MAF

(78 percent of average)

Sacramento Valley Index (SVI)

(50 percent exceedance)


(Below Normal)

San Joaquin Valley Index (SJI)

(75 percent exceedance)




Runoff: Unimpaired flows in Percent of Average for Water Year 2019

Hydrologic Region Oct








Sacramento River Region 78 56 45 53
San Joaquin River Region 65 56 43 50
Tulare Lake Region 65 55 51 55


Through the first 7-8 days of January, rivers in the Sierra Nevada are flowing well below average to start the month.

January full natural flow rates updated through January 7-8, 2019

River Basin Percent of Historic Average
Trinity 26
Shasta Inflow 43
Sacramento at Bend Bridge 45
Feather 31
Yuba 25
American 27
Cosumnes 16
Mokelumne 26
Stanislaus 36
Tuolumne 31
Merced 24
San Joaquin 35
Kings 42
Kaweah 27
Tule 26
Kern 43


Precipitation: Precipitation for Water Year 2019 accumulated at the following rates of average

Region WY accumulated precipitation (%) through December 31, 2018
Sacramento River Valley 75
San Joaquin River Valley 99
Tulare Lake Basin 105
Statewide 84
Regional Precipitation Indices Average to date

as of January 9, 2019

Northern Sierra 8-Station Index 76 (16.2 inches)
San Joaquin 5-Station Index 79 (12.1 inches)
Tulare Basin 6-Station Index 94 ( 9.9 inches)


Monthly Precipitation to date in Percent of Average for Water Year 2019 for Regional Precipitation Indices

Regional Precipitation Indices Oct Nov Dec Jan
Northern Sierra 8-Station Index 34 104 54 38
San Joaquin 5-Station Index 36 152 34 29
Tulare Basin 6-Station Index 125 163 40 31



The snowpack as of the morning of January 9, 2019 stands at the following (based on snow sensors)

Region Snow Water Equivalent (inches) % of Average (Apr 1) % of Average (Jan 9)
Northern 10.8 38 87
Central 11.4 38 88
Southern 8.6 34 87
Statewide 10.4 37 88


Weather and Climate Outlooks:

The 6-day weather forecast predicts up to 2.0, 1.0, and 0.5 inches over the Northern, Central, and Southern Sierras, respectively. The bulk of the precipitation in the Sierras is expected today. The 6-day weather forecast also predicts up to 2.5 inches on North and Central Coasts with localized precipitation amounts up to 3.5 inches near Big Sur. Freezing levels will remain near 6,000-8,000 feet over the Northern Sierras and 7,000-9,000 feet over the Central and Southern Sierras over the next six days.

The NWS Climate Prediction Center (CPC) one‐month outlook for January, posted December 31, indicates increased chances of above normal temperatures for the entire State. The same outlook suggests increased chances of above normal precipitation for the southern third of the State.

The CPC three‐month (January‐February-March) outlook, posted December 20, indicates increased chances of above normal temperatures for the entire State. The same outlook suggests increased chances of below normal precipitation for the northern third of State and equal chances of above or below normal precipitation everywhere else excluding the southern border with Arizona where increased chances of above normal precipitation are expected.

According to the latest El Niño/Southern Oscillation (ENSO) discussion issued by the Climate Prediction Center on January 7, 2019, ENSO-neutral conditions are present. Equatorial sea surface temperatures are above average across most of the Pacific Ocean. The patterns of convection and winds are mostly near average over the tropical Pacific. El Niño is expected to form and continue through the Northern Hemisphere winter 2018-2019 (~90% chance) and through spring (~60% chance).

Next Update:

The next WSI forecast for conditions as of February 1, 2019 will be available on Friday, February 8. The first Bulletin 120 of the water year 2019 will also be issued at that time. If you have any questions regarding this forecast, please contact a member of the Snow Surveys staff. 

Important Links:

Full Natural Flow Data:


Precipitation Data:


Snow Data:


Extended Regional Forecasts:



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