Water supply index for March 1st

March Snow

From the Department of Water Resources:

NEW_DWR_LOGO_14inchThe March 1, 2016 Water Supply Index (WSI) and Bulletin 120 (B120) forecasts are finished. The forecasts include observed conditions through the end of February.

The forecasts are posted at:

WSI:       http://cdec.water.ca.gov/cgi-progs/iodir/wsi

B120:     http://cdec.water.ca.gov/cgi-progs/iodir?s=b120

Forecast Summary:

February was a rather warm and dry month, with minimal precipitation and snowfall and some decent melting of the snowpack at the lower elevations.

The projected median April-July runoff in the major Sierra river basins ranges from 65 percent on the Kern River to 92 percent on the Stanislaus River. Forecasted median water year runoff in the Sierra ranges from 59 percent on the Kern River to 91 percent on the Tuolumne River.

The dry, warm conditions during February resulted in some big drops in the April-July forecasts.  Forecast changes since the February 1 forecast range from a drop of 10 percent (Kern River) to 25 percent (Mokelumne River).  While the general lack of precipitation and below average runoff play their part in impacting the April-July forecasts, the major influence on the forecast drop has to do with the snowpack.  According to the snow sensors, the snow pack on March 1 was equal to the snow pack on February 1.  February historically is one of the three wettest months in the Sierra Nevada and is also historically a significant contributor to the Sierra Nevada snowpack.  Given this, zero accumulation in the snowpack over the month was the major driving force in lowering the forecasts as much as they did between the February 1 forecast and this forecast.  This trend is also evident in the following water year forecasts.

The WSI forecast is based on hydrologic conditions observed through February 2016 and can be summarized as follows:

Sacramento River Unimpaired Runoff Water Year Forecast

(50 percent exceedance)

15.4 MAF

(84 percent of average)

Sacramento Valley Index (SVI)

(50 percent exceedance)

6.1

(Dry)

San Joaquin Valley Index

(75 percent exceedance)

2.1

(Critical)

Runoff:

Since October 1, the flows in all regions have been below average.  This trend continued in February.

Unimpaired flows for the 2015-2016 water year:

Region October-February Runoff (%) February Runoff (%)
Sacramento Valley Index (4 rivers) 82 69
San Joaquin Valley Index (6 rivers) 79 82
Tulare Lake Basin (4 rivers) 58 63

Precipitation:

February brought warm and dry weather to the State.  Precipitation fell at less than 50 percent of average in each region of the State.  Significant precipitation returned to the state in the first week of March.  This precipitation, while not captured in this forecast, will be included in the forecast update to be issued later this week.

Precipitation for the 2015-2016 water year accumulated at the following rates of average:

Region/Index WY accumulated precipitation (%) through February 29, 2016 Precipitation (%) for
February 2016
Sacramento River 104 37
San Joaquin River 100 19
Tulare Lake 114 38
Statewide 98 36
Northern Sierra 8-Station Index 102 (35.5 inches) 34 (2.7 inches)
San Joaquin 5-Station Index 99 (27.2 inches) 20 (1.4 inches)
Tulare Basin 6-Station Index 101 (19.6 inches) 21 (1.1 inches)

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.

The results of the March 2016 statewide snow surveys are as follows:

Region No. Courses

Measured

Avg WC % Average
April 1
% Average
March 1
North Coast 11 26.1″ 86% 95%
Sacramento 68 22.6″ 74% 84%
San Joaquin Valley 63 26.0″ 83% 96%
Tulare Lake 37 19.5″ 78% 88%
North Lahontan 12 21.2″ 76% 87%
South Lahontan 17 15.4″ 69% 81%
Statewide Average (weighted) 79% 89%

On March 1, the snow sensor network showed similar numbers, though slightly lower, to the March snow survey results.  As mentioned prior, the March 1 snowpack showed no gain in the water content according to the sensors in any region since February 1.  The snowpack as of the morning of March 1, 2016 stands at the following (based on snow sensors):

Region Snow Water Equivalent (inches) % of Average (Apr 1) % of Average (Mar 1)
Northern 23.1 80 89
Central 21.7 75 85
Southern 17.0 64 75
Statewide 20.7 73 83

 

Weather and Climate Outlooks:

The 6-day weather forecast indicates another series of storms bringing more precipitation to the state.  The heaviest precipitation is expected on the north coast and northern and central Sierra starting Thursday and going through the end of the 6-day window. These precipitation totals range from 8 to 10 inches.  Freezing levels are expected to rise over the next couple of days and then fall back to around 5,000 feet in the northern Sierra and around 6,000 feet in the central and southern Sierra by this weekend.

The NWS Climate Prediction Center (CPC) one-month outlook for March, issued February 29, indicates increased chances of above normal temperatures and precipitation statewide.

The CPC three-month (March-April-May) outlook, issued February 18, indicates increased chances of above normal precipitation statewide except for the northern third of the state where equal chances of above or below normal precipitation are expected.  The three month forecast also predicts increased chances of above normal temperatures statewide.

El Niño conditions are present. Positive equatorial seat surface temperature (SST) anomalies continue across most of the Pacific Ocean. A transition to ENSO-neutral is likely during late Northern Hemisphere spring or early summer 2016, with a possible transition to La Nina conditions during the fall.

Next Update:

A Bulletin 120 update for conditions as of March 8 will be available, Thursday, March 10. The April 1, 2016 Bulletin 120 and Water Supply Index forecasts will be available on Friday, April 8, 2016. If you have any questions regarding this forecast, please contact a member of the Snow Surveys staff.

Important Links:

Full Natural Flow Data:

Daily FNF: http://cdec.water.ca.gov/cgi-progs/snowsurvey_ro/FNF

Monthly FNF: http://cdec.water.ca.gov/cgi-progs/snowsurvey_ro/FNFSUM

Seasonal FNF: http://cdec.water.ca.gov/cgi-progs/snowsurvey_ro/FLOWOUT

Precipitation Data:

Latest Northern Sierra 8-Station Precipitation Index: http://cdec.water.ca.gov/cgi-progs/queryDaily?s=8SI&d=today

Latest San Joaquin 5-Station Precipitation Index: http://cdec.water.ca.gov/cgi-progs/queryDaily?s=5SI&d=today

Snow Data:

Latest Snow Sensor Report: http://cdec.water.ca.gov/cgi-progs/snow/PAGE6

Latest Statewide Summary of Snow Water Equivalents: http://cdec.water.ca.gov/cgi-progs/snow/DLYSWEQ

Extended Regional Forecasts:

California Nevada River Forecast Center 6 Day QPF and Snow Level Forecast: http://www.cnrfc.noaa.gov/awipsProducts/RNOHD6RSA.php

Climate Prediction Center One-Month Outlook Forecasts: http://www.cpc.noaa.gov/products/predictions/30day/

Climate Prediction Center Three-Month Outlook Forecasts: http://www.cpc.noaa.gov/products/predictions/long_range/seasonal.php?lead=1

U.S. Seasonal Drought Outlook: http://www.cpc.ncep.noaa.gov/products/expert_assessment/sdo_summary.html

Weather Forecast Office California Service Area-Products: http://www.cnrfc.noaa.gov/forecasts.php

El Niño Southern Oscillation (ENSO) Conditions and Weekly Discussion (including La Niña): http://www.cpc.ncep.noaa.gov/products/analysis_monitoring/lanina/enso_evolution-status-fcsts-web.pdf

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