From the Department of Water Resources:
The Department of Water Resources has finished the April 1, 2020 Water Supply Index (WSI) and Bulletin 120 (B120) forecasts. These forecasts include observed conditions through the end of March.
Due to the COVID-19 pandemic, not all snow courses normally measured in April were measured during the April 2020 snow measurement period. About 170 of the scheduled 260 courses (two-thirds) were manually measured. We’d like to give a big Shout-out to those surveyors in our wonderful cooperative snow surveyor network who went above and beyond to collect this data for this forecast and ultimately all users of this historic snowpack data set. A variety of alternative snow data sources and calculation estimates were used in place of snow course measurement data where necessary. And fortunately, because of these extraordinary surveyor efforts, we used less estimated SWE data than originally expected.
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 around 30 percent (3 smaller rivers) to 72 percent for the Pit River. The statewide seasonal AJ median forecast is 7.46 MAF which puts it at 53 percent of the historic average. This value is a 5 percent increase from the March 1 Bulletin 120 Forecast.
The projected median Water Year (WY) runoff in the major Sierra river basins ranges from 34 percent on the Tule River to 70 percent for the Pit River. The projected Statewide median WY runoff is 49 percent of the historic average.
The WSI forecast is based on precipitation, snow, and flows observed through March 2020 and can be summarized as follows:
|
Sacramento River Unimpaired Runoff Water Year Forecast (50 percent exceedance) |
9.2 MAF (52 percent of average) |
|
Sacramento Valley Index (SVI) (50 percent exceedance) |
6.0 (Dry) |
|
San Joaquin Valley Index (SJI) (75 percent exceedance) |
2.1 (Critical) |
All three indices in the table above rounded up to the values shown and so the SJI, which sits on the Dry/Critical threshold, still falls in the Critical Year Type Classification.
Runoff:
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 |
Mar Runoff |
Oct-Mar Runoff |
|
Sacramento River Region |
84 |
45 |
74 |
45 |
33 |
31 |
45 |
|
San Joaquin River Region |
92 |
33 |
84 |
26 |
26 |
41 |
40 |
|
Tulare Lake Region |
110 |
77 |
91 |
42 |
41 |
38 |
54 |
All but the Cosumnes River are flowing below average for April full natural flow rates.
April full natural flow rates updated through April 5-7, 2020:
|
River Basin |
Percent of Historic Average |
|
Trinity |
34 |
|
Shasta Inflow |
77 |
|
Sacramento at Bend Bridge |
80 |
|
Feather |
57 |
|
Yuba |
64 |
|
American |
90 |
|
Cosumnes |
119 |
|
Mokelumne |
55 |
|
Stanislaus |
54 |
|
Tuolumne |
67 |
|
Merced |
74 |
|
San Joaquin |
44 |
|
Kings |
42 |
|
Kaweah |
43 |
|
Tule |
53 |
|
Kern |
35 |
Precipitation:
Precipitation for Water Year 2020 accumulated at the following rates of average
|
Region |
WY accumulated precipitation (%) through March 31, 2020 |
|
Sacramento River Valley |
55 |
|
San Joaquin River Valley |
68 |
|
Tulare Lake Basin |
61 |
|
Statewide |
66 |
|
Regional Precipitation Indices |
WY average to date as of April 8, 2020 |
|
Northern Sierra 8-Station Index |
60 (26.9 inches) |
|
San Joaquin 5-Station Index |
62 (21.2 inches) |
|
Tulare Basin 6-Station Index |
61 ( 15.2 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 |
Apr |
|
Northern Sierra 8-Station Index |
3 |
43 |
107 |
55 |
2 |
81 |
71 |
|
San Joaquin 5-Station Index |
0 |
69 |
109 |
19 |
4 |
101 |
94 |
|
Tulare Basin 6-Station Index |
0 |
106 |
91 |
12 |
12 |
76 |
120 |
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.
Statewide, snow surveyors reported (1) soils as “damp” under the snow for 61 percent of courses measured and (2) sampling as “easy” to “moderately difficult” at all snow courses. Despite these reported sampling conditions, DWR surveyors sheared off cutters from two snow tube kits at the Castle Creek #5 course in the Yuba, due to a 3-4 inch ice layer buried approximately 60 inches below the snow surface – one at the first sample point and one at the eighth!
A dry January and February and relatively average March resulted in a below average snowpack as of April 1. April snow course measurements show the statewide average at 50 percent of average. The results of the April 2020 statewide snow surveys are as follows:
|
Region |
No. of Courses Measured |
Average Snow Water Content (inches) |
% Average |
|
North Coast |
18 |
11.5 |
41 |
|
Sacramento |
51 |
16.2 |
58 |
|
San Joaquin Valley |
43 |
14.3 |
45 |
|
Tulare Lake |
28 |
10.2 |
45 |
|
North Lahontan |
12 |
10.9 |
49 |
|
South Lahontan |
18 |
10.8 |
50 |
|
Statewide Average (weighted) |
50 |
||
As of April 8, the statewide snowpack based on the automated snow sensor network is 64 percent of average to date and 63 percent of the April 1 average. The snowpack as of the morning of April 8, 2020 stands at the following (based on snow sensors):
|
Region |
Snow Water Content (inches) |
% of Average (Apr 1) |
% of Average (April 8) |
|
Northern |
19.0 |
65 |
67 |
|
Central |
19.8 |
67 |
68 |
|
Southern |
13.8 |
54 |
55 |
|
Statewide |
17.9 |
63 |
64 |
The statewide snowpack snow water content has increased by 2.5 inches from 15.4 inches on April 1. On April 1, the snow sensor statewide snowpack was at 54 percent of average, considerably closer to the percent of average as determined by the April snow course measurements.
Weather and Climate Outlooks:
According to the CNRFC 6-day forecast, there are chances of precipitation in southern California over the next three days. The forecasted 6-day basin wide average precipitation totals in the Central Coast, Southern Coast, Tulare, and San Joaquin are 0.1, 1.0, 1.1, and 0.1 inches, respectively. The bulk of the precipitation is expected to fall over the next two days. No significant precipitation is forecasted in any other basins over the next 6 days.
Freezing elevations range from 10,000 feet in the north (Klamath) to 5,000 feet in the south (Southern California) to start the period; by the end of the 6-day forecast, freezing elevations are forecast to be relatively constant across the state, ranging from 8,000 feet in inland areas to 10,000 feet along the coast.
The NWS Climate Prediction Center (CPC) one‐month revised outlook for April 2020 issued on March 31, 2020, points to chances of below normal temperatures for Northern California and the Sierra spine while elsewhere equal chances of above or below normal temperatures. This same outlook suggests increased chances of above normal precipitation for all of California excluding a sliver of California near the Arizona border.
The CPC three-month (April-May-June) outlook, issued on March 19, 2020, points to increased chances of above normal temperatures across the State. The same outlook forecasts equal chances of above or below normal precipitation in central and southern California, and chances of below normal precipitation in northern California.
According to the latest El Niño/Southern Oscillation (ENSO) discussion issued by the Climate Prediction Center on April 6, 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 (~65% chance), continuing through summer 2020 (~55% chance).
Next Update:
A Bulletin 120 update for conditions as of April 14 will be available by Thursday, April 16. 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
