From the Department of Water Resources:
The May 1, 2017 Water Supply Index (WSI) and Bulletin 120 (B120) forecasts have now been completed. The forecasts include observed conditions through the end of April.
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 164 percent of average for the Inflow to Shasta Lake to 242 percent for the Kern River. All rivers south of Bend Bridge are expected to have AJ runoff volumes greater than 190 percent of average.
The WSI forecast is based on precipitation and flows observed through April 2017 and can be summarized as follows:
Sacramento River Unimpaired Runoff Water Year Forecast (50 percent exceedance)
39.9 MAF (224 percent of average)
Sacramento Valley Index (SVI) (50 percent exceedance)
14.9 (Wet)
San Joaquin Valley Index (75 percent exceedance)
6.2 (Wet)
Forecasting Record Water Year Runoff Volumes:
During April, the flows in the Sacramento, San Joaquin, Tulare Lake, and North Lahontan regions were greater than 200 percent of average for the month. Considering the very wet conditions from earlier months, water year flows are expected to be records for all rivers from the Feather through the Tuolumne. No AJ records are expected except for the East Carson River (242 percent of average).
Runoff:
After February and March statewide flow rates were near 400 and 155 percent of average, respectively, April followed with flows near 200 percent of average.
Unimpaired flows for the 2016-2017 water year:
Region October-April Runoff (%) April Runoff (%) Sacramento Valley Index (4 rivers) 239 211 San Joaquin Valley Index (6 rivers) 307 204 Tulare Lake Basin (4 rivers) 266 229 Accumulated October – April flows for WY 2017 set a new record of 31.2 MAF for the Sacramento Valley 4 Rivers. The previous record was 26.6 MAF in WY 1983. We had 26.4 MAF by the end of March this year.
The top three flow rates for April, considering only west-side rivers, were the Kern, Feather, and Cosumnes with rates of 296, 242, and 230 percent of average, respectively.
WY 2017 (taf) October-March WY 2017 (taf) October-April Record (taf) October-April SRR 26380 31236 26619 (1983) SJR 6654 8369 6676 (1997) TLR 2415 3336 3283 (1983) SRR – Sacramento at Bend Bridge through American rivers
SJR – Stanislaus through San Joaquin rivers
TLR – Kings through Kern rivers
Precipitation:
The 93.0 inches of precipitation measured during October-April in the Northern Sierra 8-Station Index ranks as the highest total during that period in the entire record of the 8-Station Index dating back to 1921. The previous high was 83.7 inches in 1983. As of this morning, the 8-Station Index seasonal total to date is 93.1 inches.
The 71.0 inches of precipitation measured during October-April in the San Joaquin 5-Station Index ranks as the 2nd highest total during that period in the entire record of the 5-Station Index dating back to 1913. The current October-April record is 72.8 inches in 1983. As of this morning, the 5-Station Index seasonal total to date is 71.2 inches.
The 45.8 inches of precipitation measured during October-April in the Tulare Basin 6-Station Index ranks as the 5th highest total during that period in the entire record of the 6-Station Index dating back to 1922. As of this morning, the 6-Station Index seasonal total to date is 45.9 inches.
Precipitation for the 2016-2017 water year accumulated at the following rates of average:
Hydrologic Region October-April precipitation (%) Sacramento River 198 San Joaquin River 183 Tulare Lake 177 Statewide 173
Precipitation Index Percent of Seasonal Average to Date through May 8, 2017 Northern Sierra 8-Station Index 202 (93.1 inches) San Joaquin 5-Station Index 189 (71.2 inches) Tulare Basin 6-Station Index 169 (45.9 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.
Based on the May 1 course surveys, the snowpack in all basins from the Feather through the Kern rivers is greater than 110 percent of the April 1 average except for the Tule River. The snow water content in the Mokelumne, Stanislaus, Merced, San Joaquin, Kings and Kern river basins was equal to or greater than 160 percent of the April 1 average. The statewide average of 181 percent of average ranks this year’s snowpack as the 11th highest May 1 total on record dating back to the early 1950s. The May 1 snow pack in 1983 was an astounding 289 percent of the historical record.
Of the nearly 200 snow courses that were measured during the May 1 snow survey, 16 courses recorded new May all-time records. Most courses that set new May snow survey records were in the Central Sierra and Southern Sierra.
The results of the May 2017 statewide snow surveys are as follows:
Region No. Courses Measured
Average WC (inches) % Average April 1
% Average
May 1North Coast 9 39.1 112 160 Sacramento 65 40.9 122 169 San Joaquin Valley 55 53.6 158 192 Tulare Lake 42 41.2 157 201 North Lahontan 5 34.4 138 162 South Lahontan 7 27.6 178 207 Statewide Average (weighted) 140 181 The snowpack as of the morning of May 8, 2017 stands at the following (based on snow sensors):
Region Snow Water Equivalent (inches) % of Average (Apr 1) % of Average (May 8) Northern 31.4 112 188 Central 41.9 143 204 Southern 31.7 119 171 Statewide 36.2 128 190 Weather and Climate Outlooks:
The 6-day weather forecast indicates precipitation totals near 0.1 inch on Monday and Tuesday over the southern Sierra. The forecast predicts up to 1.0 inch of precipitation over the North Coast on Thursday and up to 0.5 inch of precipitation on Friday. The forecast predicts less than 0.1 inch over the Klamath region on Saturday. Freezing levels will remain near 12,000 feet over the Sierra Nevada for the first three days of the forecast. Freezing levels will then drop to near 7,000, 8,000, and 9,000 feet for the Northern, Central, and Southern Sierra, respectively by the end of the six-day forecast period.
The NWS Climate Prediction Center (CPC) one-month outlook for May, issued April 30, indicates equal chances of above or below normal precipitation statewide except along the North Coast and along the California-Oregon border where a greater chance of below normal precipitation is forecast. The same outlook predicts increased chances of above normal temperatures eastern half of the state, elsewhere equal chances of above or below temperatures are expected.
The CPC three-month (May-June-July) outlook, issued April 20, indicates equal chances of above or below normal precipitation for all of the state. The same outlook indicates increased chances of above normal temperatures over all areas of the state.
ENSO-neutral conditions are present. Equatorial sea surface temperatures (SSTs) are near-average across the central Pacific. They are above-average in the eastern Pacific Ocean. ENSO-neutral conditions are favored to continue through at least the Northern Hemisphere spring 2017, with increasing chances for El Niño development by late summer and fall.
Next Update:
A Bulletin 120 update for conditions as of May 9, will be available on Thursday, May 11. 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
Sign up for daily email service and you’ll never miss a post!
Sign up for daily emails and get all the Notebook’s aggregated and original water news content delivered to your email box by 9AM. Breaking news alerts, too. Sign me up!
