BULLETIN 120 Forecast Update – April 26, 2022 – MAVEN'S NOTEBOOK

From the Department of Water Resources:

DWR has finished the April 26, 2022 Bulletin 120 (B120) forecast update. The forecast includes observed conditions through the morning of Tuesday, April 26, 2022.

The forecasts are posted at:

B120 Update: https://cdec.water.ca.gov/reportapp/javareports?name=B120UP
B120 Update WY Distribution: https://cdec.water.ca.gov/reportapp/javareports?name=B120DIST

Forecast Summary:

The projected median April-July (AJ) runoff ranges in the major Southern Cascades/Sacramento River basins from 24 percent of average for the Trinity River basin to 66 percent of average for the Pit River basin, in the major San Joaquin River basins from 41 percent of average for the Merced River basin to 51 percent of average for the Cosumnes River basin, and in the major Tulare basins from 18 percent of average for the Tule River basin to 44 percent of average for the Kings River basin.

Since the April 19 B120 Forecast Update was issued, the AJ forecasts for all major basins either increased or stayed the same. Forecast increases were most significant in the Feather, Yuba, American, and Cosumnes basins which all saw increases above 10 percent of average. Forecasts remain unchanged since last week in the San Joaquin and Kaweah River basins. All remaining basins saw modest increases between 1 and 6 percent of average. Forecast increases resulted from the precipitation that fell over the last week which was well above median in basins near the transition from northern to central Sierra and more modest in the more northern and southern basins.

Runoff:

Over the last week, flows in most northern basins have begun to decline from a peak at the end of last week that resulted from recent precipitation. Flows in the central and southern Sierra basins have been relatively steady over the last week. The most northerly and the most southerly basins (Trinity, Sacramento, Tule, and Kern) are all flowing at a rate roughly one third of average. Relative April flow rates in the Yuba, American, Merced, and San Joaquin have been the highest at over 70 percent of average. All remaining basins have been flowing at a rate between 50 and 70 percent of the April average.

Unimpaired flows in Percent of Average for Water Year 2022 are as follows:

River	Oct	Nov	Dec	Jan	Feb	Mar	Oct-Mar	Apr (Month to Date)
Trinity	312	195	40	46	32	28	49	28
Shasta	104	104	72	67	29	25	53	39
Sacramento at Bend Bridge	125	115	76	54	25	23	51	39
Feather	348	137	117	74	45	47	79	63
Yuba	566	163	117	58	35	42	74	73
American	814	198	144	58	40	48	80	75
*Sacramento Region*	233	131	99	60	33	35	64
Cosumnes	1334	151	254	51	28	22	66	52
Mokelumne	732	234	135	58	49	58	87	63
Stanislaus	432	161	146	47	47	56	77	63
Tuolumne	384	176	143	45	39	49	74	66
Merced	277	167	140	42	36	51	65	72
San Joaquin	282	170	215	71	67	73	102	74
*San Joaquin Region*	402	176	165	52	45	53	79
Kings	96	100	126	54	49	59	68	68
Kaweah	70	49	99	38	34	42	47	53
Tule	65	29	95	35	22	26	36	27
Kern	51	58	72	45	37	34	45	35
*Tulare Region*	76	74	104	48	41	47	56

Precipitation:

April for the northern Sierra received considerable precipitation over the last two weeks with the Northern Sierra 8-Station Index accumulating more precipitation than it did over the previous three months combined. The Northern Sierra 8-Station Index totaled 6.1 inches in April which is 141% of the April average. Some precipitation did fall on the central and southern Sierras; however, the San Joaquin 5-Station Index and Tulare Basin 6-Station Index will come in below average at approximately 62% and 44% respectively.

Precipitation summary for Water Year 2022 as of April 28, 2022:

Region	Percent of Average								Precipitation (inches)
Region	Oct	Nov	Dec	Jan	Feb	Mar	Apr (Month to Date)	WY to Date	Apr (Month to Date)	WY to Date
Northern Sierra 8-Station Index	453	58	144	14	4	16	141	81	6.1	39.3
San Joaquin 5-Station Index	314	25	195	0	2	26	62	66	2.2	24.3
Tulare Basin 6-Station Index	216	7	221	0	9	31	44	62	1.1	16.0

Snowpack:

The statewide snow water equivalent (SWE) based on snow sensors is 7.4 inches which corresponds to 32 percent of normal for this date and 26 percent of the April 1 average. Since April 1, the statewide snowpack has decreased by 2.9 inches. Snowmelt was high at the start of the month decreasing the snowpack to 6.0 inches on April 11, but recent precipitation added almost 3 inches back to the statewide snowpack creating a local peak on April 23^rd at 8.9 inches. Since April 23^rd the Statewide snowpack has steadily declined. The entire Sierras have seen significant snow over the last two weeks with the majority in the Northern Sierra.

The regional snowpack levels as of the morning of April 28, 2022 stand at the following (based on snow sensors):

Region	No. of Stations	Avg. SWC	Percent of April 1	Percent of Normal
Northern	29	6.8	24	32
Central	43	9.7	33	39
Southern	25	4.2	17	21
Statewide	97	7.4	26	32

Weather and Climate Outlooks:

According to CNRFC 6-day forecast, small amounts of precipitation is forecasted for the north coast and northern Sierra over the first five days of the forecast with the entire state being dry by the sixth day. The north coast and northeast corner of the state will see precipitation totals of less than half an inch with other impacted areas seeing less than a tenth of an inch. In the northern parts of the state, freezing levels will increase over the next 24 hours from 4,000-6,000 feet and fluctuate between 6,000-10,000 feet over four days before rising to 9,000 to 12,000 feet by the last day of the forecast. In the Central and Southern parts of the state, freezing levels will rise from current levels between 8,000 to 11,000 feet to 10,000 to 13,000 feet by the end of the forecast period.

The NWS Climate Prediction Center (CPC) one‐month (May) outlook issued on April 21, 2022, suggests equal chances of above or below normal temperatures for the coast and suggests above average chances for higher-than-normal temperatures in the remainder of the state. The same forecast suggests the northern half of the state has slightly increased chances for below normal precipitation. For the southern half of the state there is equal chances of above or below average precipitation.

The CPC three-month (May-June-July) outlook, issued on April 21, 2022, suggests equal chances of above or below normal temperatures for the central and northern coasts and for the rest of the state increased chances of above average temperatures are expected. The outlook also shows equal chances of above or below normal precipitation for the central and southern parts of the state except for a small area of the southeast corner which shows increased chances of above normal precipitation. The northern third of the state shows increased probability of below normal precipitation.

According to the latest El Niño/Southern Oscillation (ENSO) discussion issued by the CPC on April 25, 2022, La Niña conditions are present. Equatorial sea surface temperatures (SSTs) are below average across most of the Pacific Ocean. The tropical Pacific atmosphere is consistent with La Niña. These conditions are favored to continue into the Northern Hemisphere summer (59 percent chance during June-August 2022), with a 50-55 percent chance of La Niña through the fall.

Important Links:

Full Natural Flow Data: