WATER SUPPLY INDEX Forecast for April 1, 2019

A couple watch the water release from Lake Natoma at Nimbus Dam in Rancho Cordova, California, while storm clouds build in the distant sky. Photo by DWR.

From the Department of Water Resources:

The Department of Water Resources has finished the April 1, 2019 Water Supply Index (WSI) and Bulletin 120 (B120) forecasts. These forecasts include observed conditions through the end of March.

The forecasts are posted at:

Forecast Summary:

The projected median April-July (AJ) runoff in forecasted river basins ranges from 130 percent on the McCloud River to 180 percent for the Truckee River. The statewide seasonal AJ median forecast is 22.18 MAF which is 159 percent of the historic average. Since March 1, all forecasts have significantly increased from 11 percent (McCloud River) to 46 percent for the Tule River.

The projected median Water Year (WY) runoff in forecasted river basins ranges from 118 percent for the Trinity River to 172 percent for the Cosumnes River. The Klamath River inflow to Upper Klamath Lake is the lowest of our forecasted basins at 109 percent of average. The projected Statewide median WY runoff is 140 percent of average.

These forecasts do not include precipitation observed in April.

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

Sacramento River Unimpaired Runoff Water Year Forecast

(50 percent exceedance)

 24.2 MAF

(136 percent of average)

Sacramento Valley Index (SVI)

(50 percent exceedance)

 10.1

(Wet)

San Joaquin Valley Index (SJI)

(75 percent exceedance)

4.3

(Wet)

 

Runoff:

Unimpaired flows in Percent of Average for Water Year 2019

Hydrologic Region Oct Runoff Nov Runoff Dec Runoff Jan Runoff Feb Runoff Mar Runoff Oct-Mar Runoff
Sacramento River Region 78 56 45 102 176 165 122
San Joaquin River Region 65 56 43 80 229 179 140
Tulare Lake Region 65 55 51 69 183 196 129

 

April full natural flow rates updated through April 7-8, 2019:

River Basin Percent of Historic Average
Trinity 239
Shasta Inflow 260
Sacramento at Bend Bridge 244
Feather 216
Yuba 179
American 176
Cosumnes 289
Mokelumne 164
Stanislaus 146
Tuolumne 118
Merced 104
San Joaquin 119
Kings 100
Kaweah 118
Tule 147
Kern 135

 

Precipitation:

After February, when all three precipitation regions experienced at least 190 percent of average, March precipitation was 127, 129, and 163 percent of average in the Northern Sierra 8-Station, San Joaquin 5-Station, and Tulare Basin 6-Station indexes.

 

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

Region WY accumulated precipitation through March 31, 2019

(percent of average to date)

Sacramento River Valley 133
San Joaquin River Valley 130
Tulare Lake Basin 140
Statewide 131
Regional Precipitation Indices Average to date

as of April 9, 2019

Northern Sierra 8-Station Index 136 (60.6 inches)
San Joaquin 5-Station Index 125 (43.2 inches)
Tulare Basin 6-Station Index 126 (31.3 inches)

 

Monthly Precipitation for individual months (April values are through April 8) in Percent of average for Water Year 2019:

Regional Precipitation Indices Oct Nov Dec Jan Feb Mar Apr
Northern Sierra 8-Station Index 34 104 54 148 264 127 81
San Joaquin 5-Station Index 36 152 34 118 238 129 22
Tulare Basin 6-Station Index 125 163 40 103 193 163 8

 

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.

The Statewide snow surveys measured 175 percent of average for April 1. In comparison to other years, the Statewide snow surveys measured 237, 224, 227, and 182 percent of average for April 1 in 1952, 1969, 1983, and 1995, respectively. More recently, Statewide snow surveys measured 171 and 159 percent of average for April 1 in 2011 and 2017, respectively

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

 Region No. of Courses Measured Average Snow Water Content

(inches)

% Average
April 1
North Coast 15 39.3 145%
Sacramento 74 48.1 183%
San Joaquin Valley 67 51.6 171%
Tulare Lake 43 41.9 184%
North Lahontan 17 42.5 177%
South Lahontan 19 34.8 169%
Statewide Average (weighted) 175%

 

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

Region Snow Water Content (inches) % of Average (Apr 1) % of Average (Apr 9)
Northern 47.3 158 165
Central 46.9 162 164
Southern 37.3 148 151
Statewide 44.2 157 161

 

Since April 1, the Statewide snowpack has decreased about one inch of snow water content.

Weather and Climate Outlooks:

The CNRFC forecast calls for light precipitation today across North Coast, Sierra Crest, and north slopes of San Gabriels and San Bernadino Mountains. This is expected to continue throughout the day as the upper trough pushes eastward, wrapping up overnight. Tomorrow is expected to be mostly dry across the State. By Thursday, a weak storm system (inside slider) may push through Northern California, bringing light precipitation to the Upper Klamath during the daytime. This then moves into the Northern and Central Sierras later in the day, weakening overnight. On Friday, chance of light showers over the southern Sierra and Southern California. After a break on Saturday, another weak system is expected to bring light precipitation across Northern California on Sunday. According to CNRFC, the 6-day total precipitation (average) in Klamath and North Coast will be 0.2 and 0.1-inch, respectively. The 6-day totals in Feather, Yuba, and American will be 0.2, 0.2, and 0.2-inch, respectively. Basins in Central and Southern Sierra are expected to receive up to 0.1-inch of precipitation over the next 6-days.

Today, the freezing elevations will be around 5,000 to 6,000 feet over Northern California and the Sierras. The elevations go up gradually as the week progresses. By Saturday, the elevations will be around 10,000 feet across all major river basins in the State. By Sunday night, the elevations fall down to 8,000 feet.

The NWS Climate Prediction Center (CPC) one‐month outlook issued on March 31, 2019, indicates increased chances of above normal temperatures Statewide. The same outlook indicates increased chances of above normal precipitation in the northern half of the State and equal chances of above or below normal precipitation in the southern half of the State.

The CPC three‐month (April-May-June) outlook issued on March 21, indicates increased chances of above normal temperatures in the northern half of the State and equal chances of above or below normal temperatures in the southern half of the State. The same outlook indicates equal chances of above or below normal precipitation Statewide.

According to the latest El Niño/Southern Oscillation (ENSO) discussion issued by the Climate Prediction Center on April 8, 2019, El Niño 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 likely to continue through the Northern Hemisphere spring 2019 (~80% chance) and summer (~60% chance).

Next Update:

A Bulletin 120 update for conditions as of April 9 will be available Thursday, April 11. 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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