WATER SUPPLY INDEX for February 1st

From the Department of Water Resources:

The February 1, 2019 Water Supply Index (WSI) and Bulletin 120 (B120) forecasts are finished and include observed conditions through the end of January.

The forecasts are posted at:

WSI:       http://cdec.water.ca.gov/reportapp/javareports?name=WSI

B120:     http://cdec.water.ca.gov/b120.html

Forecast Summary:

The projected median April-July (AJ) runoff in the major Sierra river basins ranges from 63 percent on the Tule River to 101 percent for the Mokelumne River. The statewide seasonal AJ median forecast is 12.44 MAF which puts it at 89 percent of the historic average.

The projected median Water Year (WY) runoff in the major Sierra river basins ranges from 65 percent on the Tule River to 90 percent for the Mokelumne and Tuolumne Rivers. The projected Statewide median WY runoff is 84 percent of the historic average.

These forecasts do not include the storms that have hit California during the first week of February. The storms have not influenced these forecasts. This is a true February 1, 2019 forecast, using median conditions after February 1.

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)

 15.0 MAF

(84 percent of average)

Sacramento Valley Index (SVI)

(50 percent exceedance)

 6.9

(Below Normal)

San Joaquin Valley Index (SJI)

(75 percent exceedance)

2.8

(Below Normal)

 

Runoff:

Unimpaired flows in Percent of Average for Water Year 2019

Hydrologic Region Oct

Runoff

Nov

Runoff

Dec

Runoff

Jan

Runoff

Oct-Jan

Runoff

Sacramento River Region 78 56 45 102 75
San Joaquin River Region 65 56 43 80 65
Tulare Lake Region 65 55 51 69 61

Precipitation:

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

Region WY accumulated precipitation through January 31, 2019 (percent of average to date)
Sacramento River Valley 92
San Joaquin River Valley 99
Tulare Lake Basin 99
Statewide 94
Regional Precipitation Indices Average to date

as of February 8, 2019

Northern Sierra 8-Station Index 103 (30.9 inches)
San Joaquin 5-Station Index 114 (25.6 inches)
Tulare Basin 6-Station Index 117 ( 18.5 inches)

 

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

Regional Precipitation Indices Oct Nov Dec Jan Feb
Northern Sierra 8-Station Index 34 104 54 148 58
San Joaquin 5-Station Index 36 152 34 118 105
Tulare Basin 6-Station Index 125 163 40 103 94

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.

An above average January boosted the snowpack to average or above over all regions, see below. The Statewide snow surveys measured 110 percent of average for February 1. The last time we experienced snow accumulations similar to this was 2016.  It should also be noted last water year (2018) at this time (February 1) statewide snow survey average was just 25 percent.

The results of the February 2019 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 19.0 62% 100%
Sacramento 72 18.6 71% 111%
San Joaquin Valley 59 20.4 68% 108%
Tulare Lake 40 15.9 71% 116%
North Lahontan 11 14.5 68% 107%
South Lahontan 17 15.0 73% 116%
Statewide Average (weighted) 69% 110%

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 7, 2019 stands at the following (based on snow sensors):

Region Snow Water Content (inches) % of Average (Apr 1) % of Average (Feb 7)
Northern 21.9 77 109
Central 26.6 87 126
Southern 22.3 88 135
Statewide 24 84 123

Since February 1, the Statewide snow pack has increased 6.5 inches of snow water content, which accounts for about 23 percent increase in the April 1 average.

Weather and Climate Outlooks:

Two back to back storms are expected to bring in up to 4.5, 5.0, and 5.5 inches over the Northern, Central, and Southern Sierras, respectively, over the next 6 days. In Northern California, the bulk of precipitation falls tomorrow and Tuesday. In Central and Southern Sierras, the bulk of the precipitation falls over the weekend and Wednesday. North Coast receives a maximum of 8 inches of precipitation and a bulk of that falls over Tuesday. Freezing elevations are forecasted to be in the range of 2,000-3,000 feet in the Northern Sierra for the next 6-days except for Sunday when they will be around 1,000 feet. In the Central and Southern Sierras, freezing elevations will be around 3,000 – 4,000 feet for the next 6 days except for Sunday when they will be around 2,000 feet.

The NWS Climate Prediction Center (CPC) one‐month outlook for February, posted January 31, indicates increased chances of below normal temperatures for the northern two-thirds of the State. The same outlook indicates increased chances of above normal precipitation for the southern two-thirds of the State.

The CPC three‐month (February-March-April) outlook, posted January 17, indicates increased chances of above normal temperatures Statewide. The same outlook indicates increased chances of below normal precipitation for the northern third of the State and equal chances of above or below normal precipitation elsewhere.

According to the latest El Niño/Southern Oscillation (ENSO) discussion issued by the Climate Prediction Center on February 4, 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 spring 2019 (~65% chance).

Next Update:

A Bulletin 120 update for conditions as of February 12 will be available Thursday, February 14. The March 1, 2019 Bulletin 120 and Water Supply Index forecasts will be available on Friday, March 8, 2019. 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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