WATER SUPPLY INDEX FORECAST for March 1, 2019

Snow-covered Sierra Nevada trees to the northwest from the Phillips Station meadow where the California Department of Water Resources conducts its snow surveys. Photo taken February 28, 2019 by Ken James / California Department of Water Resources.

From the Department of Water Resources:

DWR staff have finished the March 1, 2019 Water Supply Index (WSI) and Bulletin 120 (B120) forecasts. These forecasts include observed conditions through the end of February.

The forecasts are posted at:

Forecast Summary:

The projected median April-July (AJ) runoff in the major Sierra river basins ranges from 119 percent on the Sacramento River at Delta and McCloud River to 155 percent for the Feather River. The Trinity River AJ runoff is the lowest of our forecasted basins at 113 percent of average. The statewide seasonal AJ median forecast is 19.24 MAF which puts it at 138 percent of the historic average. All forecasts have significantly increased since February 1 increasing between 30 to 70 percent of average.

The projected median Water Year (WY) runoff in the major Sierra river basins ranges from 113 percent on the Total Inflow to Shasta Lake to 145 percent for the Cosumnes River. The Trinity River WY runoff is the lowest of our forecasted basins at 99 percent of average. The projected Statewide median WY runoff is 128 percent of the historic average.

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

The WSI forecast is based on precipitation and flows observed through February 2019 and can be summarized as follows:

Sacramento River Unimpaired Runoff Water Year Forecast

(50 percent exceedance)

 22.7 MAF

(127 percent of average)

Sacramento Valley Index (SVI)

(50 percent exceedance)

 9.6

(Wet)

San Joaquin Valley Index (SJI)

(75 percent exceedance)

3.7

(Above Normal)

 

Runoff:

Unimpaired flows in Percent of Average for Water Year 2019

Hydrologic Region Oct

Runoff

Nov

Runoff

Dec

Runoff

Jan

Runoff

Feb

Runoff

Oct-Feb

Runoff

Sacramento River Region 78 56 45 102 176 106
San Joaquin River Region 65 56 43 80 229 121
Tulare Lake Region 65 55 51 69 183 98

 

March full natural flow rates updated through March 6-7, 2019:

River Basin Percent of Historic Average
Trinity 132
Shasta Inflow 224
Sacramento at Bend Bridge 240
Feather 217
Yuba 226
American 337
Cosumnes 456
Mokelumne 280
Stanislaus 307
Tuolumne 283
Merced 254
San Joaquin 221
Kings 263
Kaweah 355
Tule 445
Kern 315

Precipitation:

The 21.7 inches of precipitation in February ranks as the 3rd wettest February on record for the Northern Sierra 8-Station Precipitation Index (8SI) dating back to 1921. For the San Joaquin 5-Station Precipitation Index (5SI), the 16.0 inches of precipitation in February ranked as the 6th wettest February on record dating back to 1913. For the Tulare Lake 6-Station Precipitation Index (6SI), the 9.7 inches of precipitation this month currently ranks as the 17th wettest February on record dating back to 1922. As of the morning of March 8, the 8SI and 6SI seasonal totals to date have already surpassed their water year averages of 51.8 and 28.8 inches, respectively.

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

Region WY accumulated precipitation through February 28, 2019

(percent of average to date)

Sacramento River Valley 134
San Joaquin River Valley 131
Tulare Lake Basin 134
Statewide 130
Regional Precipitation Indices Average to date

as of March 8, 2019

Northern Sierra 8-Station Index 138 (52.5 inches)
San Joaquin 5-Station Index 136 (39.2 inches)
Tulare Basin 6-Station Index 144 (29.7 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 Mar
Northern Sierra 8-Station Index 34 104 54 148 264 61
San Joaquin 5-Station Index 36 152 34 118 238 78
Tulare Basin 6-Station Index 125 163 40 103 193 132

 

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 over 100 years.

A well above average February boosted the snowpack Statewide. The Statewide snow surveys measured 170 percent of average for March 1. In comparison to other years, the Statewide snow surveys measured 187, 125, 180, and 211 percent of average for March 1 in 2017, 2011, 1998, and 1983 respectively.

The results of the March 2019 statewide snow surveys are as follows:

 Region No. of Courses Measured Average Snow Water Content

(inches)

% Average
April 1
% Average
March 1
North Coast 8 36.9 129% 143%
Sacramento 57 37.3 172% 195%
San Joaquin Valley 54 41.5 138% 159%
Tulare Lake 34 34.1 149% 167%
North Lahontan 9 33.9 148% 168%
South Lahontan 17 29.6 139% 164%
Statewide Average (weighted) 152% 173%

The automated snow sensor network shows similar results to those found in the manual snow course readings.

The snowpack as of the morning of March 8, 2019 stands at the following (based on snow sensors):

Region Snow Water Content (inches) % of Average (Apr 1) % of Average (Mar 8)
Northern 43.3 148 156
Central 44.0 153 165
Southern 37.3 148 162
Statewide 41.9 150 161

Since March 1, the Statewide snow pack has increased 4.5 inches of snow water content, which accounts for about 16 percent increase in the April 1 average.

Weather and Climate Outlooks:

The CNRFC 6-day forecast shows light rain and snow showers (less than 0.5-inch totals) in the next 24-hours in major Sierra basins and North Coast. Dry weather is expected over the weekend, and then again light rain and snow showers ranging anywhere from 0.1-0.5-inch are expected to fall in the major Sierra basins and North Coast. The 6-day totals in the Upper Sacramento, Lower Sacramento, Feather, Yuba, and American are 0.6, 0.3, 0.6, 0.6, and 0.7-inches, respectively. Almost all of this precipitation falls in the next 24-hours and on Monday through Tuesday morning. This is the same pattern for all other basins. The 6-day totals for Klamath, North Coast, Russian, Napa, Central Coast, San Joaquin, and North San Joaquin are 0.3, 0.6, 0.5, 0.5, 0.2, 0.2, and 0.4-inches, respectively. Tulare and Southern California totals are 0.2 and 0.1-inches, respectively. Note, the precipitation amounts listed above are basin averages, some areas in the basin may get more and some may get less. The freezing elevations will be low, today, in all major basins, hovering around 3,000 to 4,000 feet. The elevations will gradually go up, and by Sunday they will be around 5,000 to 6,000 feet. After Sunday, they will gradually go down, and by mid-week they will hover around 3,000 to 4,000 feet.

The NWS Climate Prediction Center (CPC) one‐month outlook for March, posted February 28, 2019, indicates increased chances of below normal temperatures all across the State. The same outlook indicates increased chances of above normal precipitation all across the State.

The CPC three‐month (March-April-May) outlook, posted February 21, 2019, indicates increased chances of above normal temperatures all across the State. The same outlook indicates equal chances of above or below normal precipitation all across the State.

According to the latest El Niño/Southern Oscillation (ENSO) discussion issued by the Climate Prediction Center on March 4, 2019, ENSO-neutral conditions are present. Equatorial sea surface temperatures are above average across most of the Pacific Ocean. The pattern of anomalous convection and winds are consistent with El Niño. Weak El Niño conditions are expected to continue through the Northern Hemisphere spring 2019 (~55% chance).

Next Update:

A Bulletin 120 update for conditions as of March 12 will be available Thursday, March 14. The April 1, 2019 Bulletin 120 and Water Supply Index forecasts will be available on Tuesday, April 9, 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:

Click here to view all posted announcements.

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