WATER SUPPLY INDEX for February 1, 2020

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The Department of Water Resources has finished the February 1, 2020 Water Supply Index (WSI) and Bulletin 120 (B120) forecasts. These forecasts include observed conditions through the end of January. The forecasts are posted at:

 Forecast Summary:

The projected median April-July (AJ) runoff in the major Sierra river basins ranges from 52 percent for the Cosumnes River to 88 percent for the McCloud River. The statewide seasonal AJ median forecast is 9.92 MAF which puts it at 71 percent of the historic average. The projected median Water Year (WY) runoff in the major Sierra river basins ranges from 42 percent on the Cosumnes River to 72 percent for the Total Inflow to Shasta. The projected Statewide median WY runoff is 65 percent of the historic average. The WSI forecast is based on precipitation and flows observed through January 2018 and can be summarized as follows:

Sacramento River Unimpaired Runoff Water Year Forecast (50 percent exceedance) 11.6 MAF (65 percent of average)
Sacramento Valley Index (SVI) (50 percent exceedance) 6.73 (Below Normal)
San Joaquin Valley Index (SJI) (75 percent exceedance) 2.52 (Below Normal)

  Runoff: Unimpaired flows in Percent of Average for Water Year 2020

Hydrologic Region Oct Runoff Nov Runoff Dec Runoff Jan Runoff Oct-Jan Runoff
Sacramento River Region 84 45 74 47 58
San Joaquin River Region 92 33 84 26 47
Tulare Lake Region 110 77 91 42 70

Through the first 8-9 days of February, all rivers are flowing below average.

February full natural flow rates updated through February 8-9, 2020
River Basin Percent of Historic Average
Trinity 42
Shasta Inflow 46
Sacramento at Bend Bridge 43
Feather 40
Yuba 36
American 29
Cosumnes 16
Mokelumne 31
Stanislaus 29
Tuolumne 21
Merced 19
San Joaquin 28
Kings 29
Kaweah 32
Tule 25
Kern 59

 

Precipitation: Precipitation for Water Year 2020 accumulated at the following rate of average
Region WY accumulated precipitation (%) through January 31, 2020
Sacramento River Valley 63
San Joaquin River Valley 74
Tulare Lake Basin 68
Statewide 73
Regional Precipitation Indices Average to date as of February 10, 2020
Northern Sierra 8-Station Index 58 (17.8 inches)
San Joaquin 5-Station Index 48 (11.1 inches)
Tulare Basin 6-Station Index 50 ( 8.1 inches)

 

Monthly Precipitation to date in Percent of Average for Water Year 2020 for Regional Precipitation Indices
Regional Precipitation Indices Oct Nov Dec Jan Feb
Northern Sierra 8-Station Index 3 43 106 53 0
San Joaquin 5-Station Index 0 69 104 18 0
Tulare Basin 6-Station Index 0 106 89 12 0

 

Snowpack:

Snowpack is monitored using two complementary methods: automatic snow sensor (or “pillow”) readings and manual snow course measurements. The snow sensors give us a daily snapshot of snow conditions while the manual snow course measurements provide a monthly verification of snow conditions in locations where snow has been measured in the same manner as far back as 100 years. A dry January resulted in a below average snowpack as of February 1.  February snow course measurements show the statewide average at 74 percent of average. As of February 10, the statewide snowpack based on the automated snow sensor network is 60 percent of average to date and 43 percent of the April 1 average. The results of the February 2020 statewide snow surveys are as follows:

 Region No. of Courses Measured Average Snow Water Content (inches) % Average April 1 % Average February 1
North Coast 11 14.8 49 79
Sacramento 72 13.8 48 74
San Joaquin Valley 67 13.6 45 72
Tulare Lake 42 10.4 47 77
North Lahontan 11 9.4 42 67
South Lahontan 19 8.5 43 68
Statewide Average (weighted) 46 74

The automated snow sensor network shows similar results to those found in the manual snow course readings. The snowpack as of the morning of February 10, 2020 stands at the following (based on snow sensors):

Region Snow Water Content (inches) % of Average (Apr 1) % of Average (Feb 10)
Northern 13.8 47 64
Central 12.4 42 58
Southern 9.8 38 56
Statewide 12.1 43 60

Since February 1, there is no change to the statewide snowpack snow water content; it remains at 12 inches.  

Weather and Climate Outlooks:

According to CNRFC 6 day forecast, precipitation in southern California wraps up tonight and after that no precipitation in sight anywhere in the State for the whole week. A weak system forecasted to move towards northern California by the end of the week may bring in lighter amounts of precipitation over northern California down to the central Sierra. On average, approximately 0.2 inches of precipitation is expected to fall over Klamath and North Coast basins, and under 0.1 inch over northern California and central Sierra on Saturday.

Freezing elevations through Wednesday will be high all across the State ranging from 8,000 to 10,000 feet. From Thursday through Saturday, elevations will range from 6,000 to 8,000 feet except in Klamath where it will be around 5,000 feet. The NWS Climate Prediction Center (CPC) one‐month outlook for February 2020 issued on January 31, 2020, points to increased chances of above normal temperatures all across the State.

The same outlook suggests increased chances of below normal precipitation for the northern and central parts of the State, and equal chances of above or below normal precipitation for the southern part of the State. The CPC three‐month (February-March-April) outlook, issued on January 16, 2020, points to increased chances of above normal temperatures all across the State. The same outlook suggests increased chances of below normal precipitation all across the State. According to the latest El Niño/Southern Oscillation (ENSO) discussion issued by the Climate Prediction Center on February 10, 2020, ENSO-neutral conditions are present. Equatorial sea surface temperatures are near-to-above average across the Pacific Ocean. ENSO-neutral is favored through Northern Hemisphere spring 2020 (~60% chance), continuing through summer 2020 (~50% chance).

Next Update: A Bulletin 120 update for conditions as of February 11 will be available Thursday, February 13. The March 1, 2020 Bulletin 120 and Water Supply Index forecasts will be available on Monday, March 9, 2020. 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:

Bulletin 120: Historical forecast error plots can now be accessed at the link below. The plots compare actual and forecasted Bulletin 120 runoff projections for individual basins through WY 2018.

 

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