Rainfall during the first two weeks of April brought the most CA mountainous basins to about 50% of normal for the month of April. Valley locations in CA and all of Nevada had below normal precipitation.
April 1st Snow water content for the State came in at 87% according to snow surveys, with above normal SWE in the Northern watersheds, and below normal in the Central and Southern Sierra watersheds. Early April warm temperatures are feeding some early melt.
Figure 2. CA snow water content by region. Source: CA Department of Water Resources
Trends in the water year forecasts for the Sacramento and San Joaquin Valley Water Resources Index locations are trending downward. Today the Sacramento Water Supply Index forecast reached 120% of average, but the San Joaquin Index is only at 75% of average.
Figure 3a. Water year forecast trends for the Sacramento Valley Water Supply Index. Source: CNRFC
Figure 3b Water year forecast trends for the San Joaquin Valley Water Supply Index. Source: CNRFC
The last week of April is expected to be near average according to the Climate Prediction Center, with a slight lean towards above average in the central and southern portions of CA. Also temperatures are expected to be near normal, except in Nevada and N. California. Overall, snowmelt runoff will not vary greatly from average conditions for late April.
Figure 4 a. & b. - Climate Prediction Center (CPC) Week 2 precipitation and temperature outlooks (Source - Precipitation: CPC & Temperature: CPC)
May Outlook
Not one of the international climate models looking out into May 2025 shows above normal precipitation. Therefore, the International Multi-Model Ensemble (IMME) is predicting normal to below normal precipitation for May, but the confidence in the outlook is low (40-50% chance)
Figure 5 - Climate Prediction Center (CPC) IMME forecast of May, 2025, precipitation anomalies. (Source: CPC)
The April-July snowmelt season is in full swing with some early warm temperatures and some small precipitation chances this week. The rest of April however should see some slowing of the melt.
Most likely we’ll have a second year in a row with near normal runoff statewide in CA, with a north-south gradient however. Therefore, the central and southern Sierra will likely be below normal (but near the median).
Pete Fickenscher
CNRFC
