The Department of Water Resources has finished the March 1, 2020 Water Supply Index (WSI) and Bulletin 120 (B120) forecasts. These forecasts include observed conditions through the end of February.
The forecasts are posted at:
WSI: http://cdec.water.ca.gov/reportapp/javareports?name=WSI
B120: http://cdec.water.ca.gov/b120.html
Forecast Summary:
The projected median April-July (AJ) runoff in the major Sierra river basins ranges from 24 percent for the Cosumnes River to 78 percent for the McCloud River. The statewide seasonal AJ median forecast is 6.73 MAF which puts it at 48 percent of the historic average. This is a 23 percent drop from the February 1 Bulletin 120 Forecast.
The projected median Water Year (WY) runoff in the major Sierra river basins ranges from 24 percent on the Cosumnes River to 61 percent for the Total Inflow to Shasta. The projected Statewide median WY runoff is 48 percent of the historic average.
The WSI forecast is based on precipitation and flows observed through February 2020 and can be summarized as follows:
|
Sacramento River Unimpaired Runoff Water Year Forecast (50 percent exceedance) |
9.1 MAF (51 percent of average) |
|
Sacramento Valley Index (SVI) (50 percent exceedance) |
5.9 (Dry) |
|
San Joaquin Valley Index (SJI) (75 percent exceedance) |
1.9 (Critical) |
Runoff:
February runoff for the 8 River Index (8RI) (sum of Bend, Feather, Yuba, American, Stanislaus, Tuolumne, Merced, and San Joaquin) ranked 12th driest on record dating back to 1906. However the seasonal runoff volume for October-February for the 8RI ranked 24th driest dating back to 1906. Unimpaired flows in Percent of Average for Water Year 2020 are as follows:
|
Hydrologic Region |
Oct Runoff |
Nov Runoff |
Dec Runoff |
Jan Runoff |
Feb Runoff |
Oct-Feb Runoff |
|
Sacramento River Region |
84 |
45 |
74 |
45 |
33 |
50 |
|
San Joaquin River Region |
92 |
33 |
84 |
26 |
26 |
40 |
|
Tulare Lake Region |
110 |
77 |
91 |
42 |
41 |
61 |
Through the first 5 days of March, all rivers are flowing well below average:
|
River Basin |
Percent of Historic Average |
|
Trinity |
20 |
|
Shasta Inflow |
26 |
|
Sacramento at Bend Bridge |
27 |
|
Feather |
20 |
|
Yuba* |
23 |
|
American |
18 |
|
Cosumnes |
8 |
|
Mokelumne |
25 |
|
Stanislaus |
30 |
|
Tuolumne |
25 |
|
Merced |
19 |
|
San Joaquin |
25 |
|
Kings |
29 |
|
Kaweah |
26 |
|
Tule |
19 |
|
Kern |
42 |
* based on only one day of flow
Precipitation:
February precipitation in the Northern Sierra set a new record for the driest February dating back to 1921 based on the 8-Station Index. February precipitation in the San Joaquin Hydrologic Region ranked 3rd driest dating back to 1913 based on the 5-Station Index. February precipitation in the Tulare Lake Hydrologic Region ranked 2nd driest dating back to 1922 based on the 6-Station Index. January-February 2020 precipitation in the San Joaquin and Tulare Lake Hydrologic Regions ranked as the driest on record during that two month period based on the 5-Station Index and 6-Station Index, respectively.
Precipitation for Water Year 2020 accumulated at the following rates of average
|
Region |
WY accumulated precipitation (%) through February 29, 2020 |
|
Sacramento River Valley |
49 |
|
San Joaquin River Valley |
56 |
|
Tulare Lake Basin |
52 |
|
Statewide |
57 |
|
Regional Precipitation Indices |
WY average to date as of March 6, 2020 |
|
Northern Sierra 8-Station Index |
48 (18.1 inches) |
|
San Joaquin 5-Station Index |
42 (11.9 inches) |
|
Tulare Basin 6-Station Index |
43 ( 8.8 inches) |
Monthly Precipitation to date in Percent of Average for Water Year 2020 for Regional Precipitation Indices
|
Regional Precipitation Indices |
Oct |
Nov |
Dec |
Jan |
Feb |
Mar |
|
Northern Sierra 8-Station Index |
3 |
43 |
107 |
55 |
2 |
0 |
|
San Joaquin 5-Station Index |
0 |
69 |
109 |
19 |
4 |
1 |
|
Tulare Basin 6-Station Index |
0 |
106 |
91 |
12 |
12 |
0 |
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 snowpack over the last decade has been alternating between extreme wet and dry. Out of the smallest 10 snowpacks as of March 1, five of those occurred between 2012-2020 (2015, 2018, 2014, 2012, and 2020). In contrast, the snowpack as of March 1 in 2017 and 2019 both rank in the top 10 largest snowpacks based on snow courses dating back to 1950.
A dry January and February resulted in a below average snowpack as of March 1. March snow course measurements show the statewide average at 43 percent of average. Based on March snow course measurements, the WY2020 snowpack ranks as the 9th smallest snowpack dating back to 1950. The results of the February 2020 statewide snow surveys are as follows:
|
Region |
No. of Courses Measured |
Average Snow Water Content (inches) |
% Average |
% Average |
|
North Coast |
10 |
12.8 |
41 |
45 |
|
Sacramento |
66 |
12.1 |
39 |
44 |
|
San Joaquin Valley |
64 |
11.2 |
34 |
39 |
|
Tulare Lake |
40 |
9.6 |
40 |
45 |
|
North Lahontan |
11 |
12.0 |
37 |
42 |
|
South Lahontan |
19 |
8.1 |
41 |
49 |
|
Statewide Average (weighted) |
38 |
43 |
||
As of March 6, the statewide snowpack based on the automated snow sensor network is 40 percent of average to date and 37 percent of the April 1 average. The snowpack as of the morning of March 6, 2020 stands at the following (based on snow sensors):
|
Region |
Snow Water Content (inches) |
% of Average (Apr 1) |
% of Average (Mar 6) |
|
Northern |
11.9 |
41 |
44 |
|
Central |
11.2 |
37 |
40 |
|
Southern |
8.5 |
33 |
37 |
|
Statewide |
10.6 |
37 |
40 |
The statewide snowpack snow water content has decreased slightly by 0.4 inches from 11.0 inches on March 1.
Weather and Climate Outlooks:
According to the CNRFC 6 day forecast, chances of precipitation in northern California over the weekend with moderate amounts of snow in the Sierra. Widespread moderate to locally heavy precipitation expected in central and southern California (south of I-80) on Tuesday and Wednesday. The forecasted 6-day basin wide average precipitation totals in the Klamath, North Coast, Russian and Napa are 0.3, 0.3, 0.2, and 0.2 inches, respectively. Upper Sacramento, Feather, Yuba, American, and Lower Sacramento basins are expected to receive 0.4, 0.7, 0.7, 1.0, and 0.3 inches of precipitation, respectively over the 6-day forecast period. During the same period, North San Joaquin, San Joaquin, and Tulare basins are expected to receive 0.6, 0.7, and 0.7 inches of precipitation. The highest amounts of precipitation will be over the Central Coast and Southern California; expected totals are 0.9 and 2.0 inches, respectively.
Freezing elevations range from 8,000 feet in the north (Klamath) to 10,000 feet in the south (Southern California) to start the period; and will drop to 4,000 feet in the north and 5,000 feet in the south over the weekend. Elevations gradually go up from Monday through mid-week, and by Wednesday they range from 7,000 feet in the north to 8,000 feet in the south.
The NWS Climate Prediction Center (CPC) one‐month revised outlook for March 2020 issued on February 29, 2020, points to equal chances of above or below normal temperatures across the State. The same outlook suggests increased chances of above normal precipitation in central and southern California and equal chances of above or below normal precipitation in northern California.
The CPC three‐month (March-April-May) outlook, issued on February 20, 2020, points to increased chances of above normal temperatures across the State. The same outlook suggests increased chances of below normal precipitation across the State.
According to the latest El Niño/Southern Oscillation (ENSO) discussion issued by the Climate Prediction Center on March 2, 2020, ENSO-neutral conditions are present. Equatorial sea surface temperatures (SSTs) are near-to-above average across the Pacific Ocean. The tropical atmospheric circulation is generally consistent with ENSO-neutral. ENSO-neutral is favored through Northern Hemisphere spring 2020 (~60% chance), continuing through summer 2020 (~50% chance).
Next Update:
A Bulletin 120 update for conditions as of March 10 will be available by Thursday, March 12. The April 1, 2020 Bulletin 120 and Water Supply Index forecasts will be available on Wednesday, April 8, 2020. If you have any questions regarding this forecast, please contact a member of the Snow Surveys and Water Supply Forecasting Section.
Important Links:
Full Natural Flow Data:
- Daily FNF: http://cdec.water.ca.gov/reportapp/javareports?name=FNF
- Monthly FNF: http://cdec.water.ca.gov/reportapp/javareports?name=FNFSUM
- Seasonal FNF: http://cdec.water.ca.gov/reportapp/javareports?name=FLOWOUT
Precipitation Data:
- Latest Northern Sierra 8-Station Precipitation Index: http://cdec.water.ca.gov/cgi-progs/products/TAB_ESI.pdf
- Latest San Joaquin 5-Station Precipitation Index: http://cdec.water.ca.gov/cgi-progs/products/TAB_FSI.pdf
- Latest Tulare Basin 6-Station Precipitation Index: http://cdec.water.ca.gov/cgi-progs/products/TAB_TSI.pdf
Snow Data:
- Latest Snow Sensor Report: http://cdec.water.ca.gov/reportapp/javareports?name=PAGE6
- Latest Statewide Summary of Snow Water Equivalents: http://cdec.water.ca.gov/reportapp/javareports?name=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
Bulletin 120:
Historical forecast error plots can now be accessed at the link below. The plots compare actual and forecasted Bulletin 120 runoff projections for individual basins through WY 2018.
Historical Forecast Error Plots: http://cdec.water.ca.gov/snow/bulletin120/B120_error_fcast_plots.html
