Department of Water Resources issues February Water Supply Index

NEW_DWR_LOGO_14inchThe Department of Water Resources has completed the February 1, 2014 Water Supply Index (WSI) and Bulletin 120 (B120) forecasts which include observed conditions through the end of January.

Forecast Summary:

The projected median April-July runoff in the major Sierra river basins ranges from 14 percent on the Tule River to 55 percent on the Pit River.  Forecasted median Water Year runoff ranges from 16 percent for the Tule River to 43 percent for the Total Inflow to Shasta Lake.  These first 4 months of this water year have been persistently dry, but remember California climate has also been persistently variable too.  The WSI forecast can be summarized as follows:

Sacramento River Unimpaired Runoff Water Year Forecast                       6.2 MAF

(50 percent exceedance)                                                                               (34 percent of normal)

Sacramento Valley Index (SVI)                                                                    3.7

(50 percent exceedance)                                                                               (Critical)

San Joaquin Valley Index (SJI)                                                                   1.1

(75 percent exceedance)                                                                               (Critical)

Runoff:

The low flows this winter are a true reflection of the lack of storm systems moving through California.  Monthly Flows from October through January have not exceeded 82 percent of normal for any forecasted river.  During January, no major Sierra rivers flowed at a rate greater than 45 percent of normal and the statewide average was 8 percent.  The January flows in the Sacramento River, San Joaquin River and Tulare Lake regions were 13, 6 and 7 percent of average, respectively.

Precipitation:

Water Year 2013 -14 continues the persistent dry pattern. The Northern Sierra 8-Station Precipitation has been equal to or less than 25 percent of the monthly average for all months excluding October which was 27% of normal. January only added 1.2 inches of precipitation to the 8-Station total which amounts to just 13% of the historic monthly average.  The 4.5 inches recorded by the end of January in the Northern Sierra represents 17 percent of average to date and 9 percent of the average Water Year total. This seasonal total-to-date is the all time driest October through January since 1921.

The San Joaquin region is also behaving the same as the Sacramento with the same persistent dry pattern.  The San Joaquin 5-Station Index was equal to or less than 22 percent of the monthly average for all months excluding October which was 45% of normal. January added 1.7 inches of precipitation to the 5-Station Index (a half an inch greater than the Northern Sierra). This represents just 22% of the historic monthly average.  The 4.7 inches of precipitation recorded by the end of January in the San Joaquin region represents 23 percent of average to date and 12 percent of the average Water Year total.  This annual total is the 3rd driest October through January since 1905.

At the conclusion of the first four months of the water year, precipitation (based on all available reporting gages per basin) in the Sacramento River Region was 15 percent of average to date, the San Joaquin River Region was 21 percent of average to date, and the Tulare Lake Region was 24 percent of average to date.  Statewide, water year cumulative precipitation through January was 20 percent of average to date.  The Statewide cumulative precipitation through January was 10 percent of the historic water year average.

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.

On February 1, snow sensors recorded a snow pack that was 5 percent of average in the Northern Sierra, 17 percent of average in the Central Sierra, and 20 percent of average in the Southern Sierra.  Statewide, snow water equivalent based on snow pillow data was 14 percent of the historical February 1 average and 9 percent of the historical statewide April 1 average.

Results from the 209 snow courses measured this month revealed a shallow snow pack with small, non-continuous areas of coverage.  Measurements in the Sacramento River Valley watersheds recorded a snow pack that is 5 percent of the historical February 1 average.  Measurements in the San Joaquin Valley watersheds indicated a snow pack that is 11 percent of the February 1 average while the snow pack for the Tulare Lake region was 12 percent of the February 1 average.  Statewide the snow pack was measured at 9 percent of the February 1 average and 6 percent of the historical April 1 average.

These measurements set the record for the driest statewide February 1 snowpack since World War II when the bulk of the existing snow course network was in place. There were 55 snow courses which had no snow water content available to be reported, while two courses could not be accessed via their normal means of transportation (snowmobile or ATV) because of the conditions within the watershed.  Several snow survey crews visited snow courses more than once to report the latest gains in the snow pack which came around February 1st.

Weather and Climate Outlook:

After a dry October through January period, storms have arrived this February.  For the next six days storms track primarily across the northern third of the state. For some areas of the North Coast beginning tomorrow nearly 7 inches has been forecasted while up to 3.5 inches have been forecasted for the Upper Sacramento watershed.  Unfortunately, only a half an inch is forecasted for the Lower Sacramento and only trace amounts are forecasted for the San Joaquin watershed.  Over the Northern Sierra, the freezing levels will be at their lowest today, 7000 feet, and increase through Friday.  Current freezing levels are near 9000 feet over the central and Southern Sierra.  Rising freezing levels are expected through Friday.

The NWS Climate Prediction Center’s (CPC) one-month outlook for February, last updated on January 31, 2014, suggests increased chances of above normal temperatures for California. The only exception is a sliver of Northern California ranging from Redding northward with equal chances of above or below average temperatures. The same outlook predicts increased chances of below normal precipitation ranging from Sacramento southward. The portion of California north of Sacramento is predicted to have equal chances of above or below average precipitation.

The CPC’s three-month outlook (February through April), last updated on January 16, 2014, suggests increased chances of above normal temperatures for all of California. The same outlook predicts increased chances of below normal precipitation for California with the exception of the corner near Oregon and Nevada with equal chances of above or below average precipitation.

Next Update:

A Bulletin 120 Update for conditions on February 11 will be available Thursday, February 13.  The March 1, 2014 Bulletin 120 and Water Supply Index forecasts will be available on March 10, 2014.

The forecasts are posted at:

Important Links

Full Natural Flow Data:

Precipitation Data:

Snow Data:

Extended Regional Forecasts:

Drought Information:

 

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