DWR issues Water Supply Index forecast for January 2014

It’s dry out there, no doubt!  How dry?  According to DWR’s latest Water Supply Index forecast, the flows in the north state’s rivers in August 2011 were nearly 300 percent of the flows during December 2013!  Find out more in the latest Water Supply Index forecast, issued by DWR today:

dwrlogoIt is over.  The record-breaking calendar year of 2013 has ended.  Is another dry year beginning?

Three months of observed data for Water Year (WY) 2014 are available and the dryness of the previous two years has continued into a third making water supply forecasts for California the focus of much attention on a state and national level.

The second Water Supply Index forecast of Water Year 2014 is completed.

Forecast Summary:

A Water Year 2014 Water Supply Index (WSI) forecast for conditions as of January 1, 2014 is posted at http://cdec.water.ca.gov/cgi-progs/iodir/WSI.2014. The accretions forecast will be sent at a later time. This WSI forecast is based on the precipitation and flows through December 2013 and can be summarized as follows:

Sacramento River Unimpaired Runoff Water Year Forecast                  8.9 MAF
(50 percent exceedance)                                                                             (49 percent of normal)

Sacramento Valley Index (SVI)                                                                  4.5
(50 percent exceedance)                                                                             (Critical)

San Joaquin Valley Index (SJI)                                                                   1.2
(75 percent exceedance)                                                                             (Critical)

Runoff:

Unimpaired flows (FNF), for the first three months of the Water Year, have occurred at average rates of 33 percent, 15 percent, and 28 percent of average for the Sacramento River, San Joaquin River, and the Tulare Lake regions, respectively.  During December, the flows in these three regions were 20, 10, and 22 percent of average.

To understand the uniqueness of the December flows, consider a comparison to August of Water Year 2011: For all main stem forecast points in the Department of Water Resource’s Bulletin 120 report, the August flows in WY 2011 were greater than the December flows for WY 2014.  The summation of the flows for all these rivers was greater in August 2011 not by a small factor…the flows in August 2011 were nearly 300 percent of the flows during December 2013.

The total seasonal FNF for the Sacramento 4 Rivers, San Joaquin 4 Rivers, and Tulare Basin rivers rank at about the 95%  exceedence level.  Given the dryness of the previous two WYs, one can’t expect base flow to add any significant volume to the flows this year.

Precipitation:

Unfortunately, the precipitation for October-December for the Sacramento River Region is at 16 percent of average and the San Joaquin River region is at 27 percent of average.   Statewide, cumulative water year precipitation through December is about 26 percent of average.

The Northern Sierra 8-Station Precipitation Index gained 0.9 inch in December (11 percent of average). The 8-station seasonal average is 19 percent of average through December. The San Joaquin 5-Station Index gained 1.1 inch in December (18 percent of average) and has a seasonal value of 23 percent of average through December.

The Tulare Lake region registered about 18 percent and 32 percent of the December and Oct-Dec averages, respectively.

The statewide precipitation for the last 27 months has been about 70 percent of average.

Snowpack:

On the morning of January 1, 2014, the snowpack based on sensors was 11, 22 and 30 percent of normal for the Northern, Central and Southern Sierra regions, respectively.  The statewide percent of average-to-date was 20, and the statewide percent of April 1 average is only 7.

A small sample of snow courses in the Feather, American, and San Joaquin basins indicate that the January 1 percent of average was 9, 26, and 25, respectively.

Weather and Climate Outlooks:

The latest weather forecasts for the Northern Sierra indicate less than 0.4 inches of precipitation on Saturday.  The central and southern Sierra, however, are expected to receive negligible amounts from this system.  Current freezing levels over the northern Sierra are about 8500 feet.  On Friday, as the modest warm front moves through the northern Sierra, the level is expected to be near 10500 feet.  During the rain event, snow levels will be from 6000 to 8000 feet.

Freezing levels over the central and southern Sierra, during the next 6 days, are expected to fluctuate between 9000 and 12000 feet.  High freezing elevations will be on Friday and Tuesday.

The one-month outlook for January, issued December 31, indicates an increased chance of below normal precipitation for the entire state with above normal temperatures for the Sierra.

The NWS Climate Prediction Center three-month (January-March) forecast, issued December 19, suggests an increased chance of below normal precipitation for the southern 2/3 of the state.

Next Update:

The next WSI forecast and the first Bulletin 120 forecast  should be available on February 10, 2014.  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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