The December 19th - December 27 storms quickly reversed the dry start to December. For much of the region, the December precipitation deficit was removed. Compared to December precipitation averages, portions of the Northern Sierra, Transverse Range and the Los Angeles area received upwards of 200% - 350% of their December precipitation average (see below).
Figure 1 - December 2025 percent of normal precipitation estimated by CNRFC.
Soils also responded to the recent storms with soils wetting to above average for December 30th for much of the region. The CNRFC tracks soil moisture using the Sacramento Soil Moisture Accounting model (SAC-SMA). Northern California soils experienced the largest change in comparison to the December 15th values as shown below. Moving forward, if the wet pattern continues, saturated soils will allow precipitation to generate runoff more efficiently.
Figure 2 - CNRFC SAC-SMA soil moisture model percent of normal for Dec 30th and Dec 15th.
Prior to the December 19th - December 27th storms, snowpack (snow water equivalent - SWE) was well below normal for much of the domain as depicted by Figure 3. CNRFC uses the Snow17 model to track SWE across our modeled basins. While the recent storms helped SWE conditions to improve, much of the Sierra remains below normal as of December 30th. The lack of recovery is attributed to much of the recent precipitation falling as rain due to warm storms. Some portions of the Feather basin did receive a decent amount of snowfall during the latter part of the storms, in particular, the backside of the Sierra near Susanville.
Figure 3 - CNRFC Snow17 model SWE percent of normal for Dec 30th and Dec 15th.
The April-July forecasted runoff volumes shifted upward compared to the December 15th water resource update. The increase in water supply is attributed somewhat to the recent storms but also incorporates the upcoming forecasted precipitation this weekend and into next week. The upward trend can be seen in the Central Valley Index trend plot shown in Figure 4. It is important to note the warm temperatures of the recent storms did allow for some significant observed daily runoff shown by the light gray traces. As of December 31st, the Central Valley Index April-July forecast sits at 107% of the mean and 133% of the median.
Figure 4 - April-July runoff forecast trend plot for the Central Valley Index including contributions from Bend Bridge, Oroville, Englebright, Folsom, Millerton, New Exchequer, New Don Pedro, and New Melones.
In general, the April-July runoff forecasts improved and are near to above normal for most of the Sierra.
Figure 5 - April-July runoff projections for Dec 31st, 2025 as a percentage of average and median.
After this weekend’s storms, the Climate Prediction Center is favoring near normal precipitation for much of CA and NV for January 8th through January 14. Normal temperatures are also favored for the same time period.
Figure 6 - Climate Prediction Center 8-14 day outlook published on December 31st, 2025.
