Record runoff predicted for the spring
From the Department of Water Resources:
The March 1, 2017 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:
The projected median April-July (AJ) runoff in the major Sierra river basins ranges from 131 percent on the Inflow to Lake Shasta to 269 percent on the Kern River. All rivers south of the Sacramento River are forecast to have AJ runoff greater than 160 percent of average. The forecasts for Inflow to Lake Shasta and the Sacramento River at Bend Bridge are 131 and 134 percent, respectively.
The projected median water year forecasts for the Feather, Yuba, American, Cosumnes, Truckee, and East Carson are predicting records. The Yuba and American water year 90 percent exceedance is also projecting a record. Additionally, the water year 10 percent exceedance forecast is predicting records for Inflow to Lake Shasta, Feather, Yuba, American, Cosumnes, Mokelumne, Stanislaus, Tuolumne, Merced, San Joaquin, Kings, and Kern rivers.
The WSI forecast is based on precipitation and flows observed through February 2017 and can be summarized as follows:
Sacramento River Unimpaired Runoff Water Year Forecast (50 percent exceedance)
37.1 MAF (208 percent of average)
Sacramento Valley Index (SVI) (50 percent exceedance)
13.9 (Wet)
San Joaquin Valley Index (75 percent exceedance)
5.9 (Wet)
Runoff:
After January, which had a statewide flow over 250 percent of normal, February followed with a greater flow rate of near 400 percent of average. The flow rate in the six rivers in the San Joaquin River and the North Lahontan basins flowed at rates of nearly 600 percent of the average February rate. Water Year to date flows in the Sacramento, San Joaquin, and Tulare Lake regions were 282, 426, and 307 percent of average which is a remarkable reversal of the anemic flows of recent years.
The February flows for all major rivers on the west side of the Sierra were records except for the Sacramento River at Bend Bridge and the Kings River. The February flow for the Kings River was only 1,000 AF less than the record.
The combined flows for January and February were also records for the Inflow to Shasta, the Kern River, and all rivers on the west side of the Sierra from the Feather River south to the Kings River. For the Cosumnes River, the combined flows for January and February this year were a record 754 TAF which is nearly twice the average water year total for that watershed. In fact, February’s total flow of 433 TAF nearly exceeded the previous January-February record runoff total by itself. Similar statistics exist in the Stanislaus River where nearly an entire average water year runoff was observed in the January-February period.
The flows in the San Joaquin River basin (Cosumnes through San Joaquin rivers), for February 2017, were over twice that of the last five Februarys combined.
Unimpaired flows for the 2016-2017 water year:
Region October-February Runoff (%) February Runoff (%) Sacramento Valley Index (4 rivers) 282 431 San Joaquin Valley Index (6 rivers) 426 589 Tulare Lake Basin (4 rivers) 307 482 Precipitation:
The 47.0 inches of precipitation measured during January-February in the Northern Sierra 8-Station Index ranks as the highest total during that two month span in the entire record of the 8-Station Index. The previous high was 40.0 inches in 1998. According to the historic record, there have been 46 times that an entire water year measured less than 47.0 inches in the Northern Sierra. The October-February total of 76.6 inches also ranks as the wettest in the Northern Sierra during this period. The next wettest was 1956 at 64.9 inches through the end of February.
The 42.9 inches of precipitation measured during January-February in the San Joaquin 5-Station Index ranks as the highest total during that two month span in the entire record of the 5-Station Index. The previous high was 38.4 inches in 1969. According to the historic record, there have been 69 times that an entire water year measured less than 42.9 inches in the San Joaquin Region. The October-February total of 60.6 inches also ranks as the wettest in the San Joaquin Region during this period. The next wettest was 1969 at 57.3 inches through the end of February.
The 30.0 inches of precipitation measured during January-February in the Tulare Lake Basin 6-Station Index ranks as the second highest total during that two month span in the entire record of the 6-Station Index. The current high is 34.9 inches in 1969. According to the historic record, there have been 57 times that an entire water year measured less than 30.0 inches in the Tulare Lake Basin Region. The October-February total of 40.9 inches also ranks as the second wettest in the Tulare Lake Basin Region during this period. The wettest was 1969 at 46.1 inches through the end of February.
For February, the 8-Station, 5-Station, and 6-Station precipitation indices were the 2nd, 5th, and 14th wettest on record, respectively.
Precipitation for the 2016-2017 water year accumulated at the following rates of average:
Hydrologic Region October-February precipitation (%) Sacramento River 215 San Joaquin River 211 Tulare Lake 215 Statewide 190
Precipitation Index Percent of Seasonal Average to Date through March 8, 2017 Northern Sierra 8-Station Index 213 (77.8 inches) San Joaquin 5-Station Index 212 (61.8 inches) Tulare Basin 6-Station Index 202 (41.8 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.
Water year 2017 continues to build upon an already heavy snowpack. The snowpack in the San Joaquin, Tulare Lake, and both North and South Lahontan regions are above 200% of their March 1 historical average and above 175% of their expected April 1 total. The Sacramento and North Coast regions are also above their expected April 1 total. Of particular note, the snow pack in the Kern River watershed is at 262% of its March 1 average and the snow in the Owens River basins is at 272% of the March 1 average. Snow gaugers in these regions (and others) are reporting record breaking measurements for individual courses. Once again we would like to recognize the snow surveying crews across the state for their tremendous efforts – many teams are arriving at snow surveying cabins which are buried to the top in this epic snowpack. That makes a long day even longer.
The results of the March 2017 statewide snow surveys are as follows:
Region No. Courses Measured
Avg WC % Average
April 1% Average
March 1North Coast 11 34.3″ 121% 134% Sacramento 68 41.1″ 141% 160% San Joaquin Valley 61 54.3″ 178% 205% Tulare Lake 37 47.4″ 200% 225% North Lahontan 11 47.5″ 187% 212% South Lahontan 16 45.8″ 218% 257% Statewide Average (weighted) 164% 187%
The automated snow sensor network shows similar results at the statewide level to those found in the manual snow course readings.
The snowpack as of the morning of March 8, 2017 stands at the following (based on snow sensors):
Region Snow Water Equivalent (inches) % of Average (Apr 1) % of Average (Mar 8) Northern 42.3 151 159 Central 51.7 177 191 Southern 46.8 173 189 Statewide 47.6 168 180 Weather and Climate Outlooks:
The 6-day weather forecast indicates precipitation over only the North Coast. The majority of the expected precipitation will fall today and tomorrow with totals ranging from 0.25 inch up to 1.25 inches over the two day period. Trace amounts of precipitation are expected on Monday over the same region. Freezing levels will remain high over the six-day period. Freezing levels are at their lowest today near 9,000 to 11,000 feet over the Sierras and are expected to increase slightly by the end of the six-day forecast period.
The NWS Climate Prediction Center (CPC) one-month outlook for March, issued February 28, indicates increased chances of above normal precipitation for the northern quarter of the State, equal chances of above or below normal precipitation through the Interstate-80 corridor, and increased chances of below normal precipitation for the southern half of the State. The same outlook predicts equal chances of above or below normal temperatures for the northern third of the State and increased chances of above normal temperatures elsewhere.
The CPC three-month (March-April-May) outlook, issued February 16, indicates equal chances of above or below normal precipitation statewide except for the portion along the border between southern Nevada and Arizona where the outlook indicates increased chances of below normal precipitation. The same outlook predicts equal chances of above or below normal temperatures for the northern two-thirds of the State and increased chances of above normal temperatures elsewhere.
ENSO-neutral conditions are present. Equatorial sea surface temperatures are near-average across the central and east-central Pacific. They are above average in the eastern Pacific Ocean. ENSO-neutral conditions have returned and are favored to continue through at least the Northern Hemisphere spring 2017.
Next Update:
A Bulletin 120 update for conditions as of March 14 will be available on March 16. The April 1, 2017 Bulletin 120 and Water Supply Index forecasts will be available on Monday, April 10, 2017. 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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