April Precipitation
As of today, the precipitation for the state has been below normal. The Northern Sierra has ranged from 40-60% of normal while the Southern Sierra has been 80% to 100% of normal. The Eastern Sierra has been roughly between 50-80% of normal depending on the area.
Snowpack
Snowpack was about 115% of normal statewide as of our last water resource updated on April 11th. Since then the snowpack has dropped to just below normal. This is due to both the below normal April precipitation, and the higher than expected snowmelt during the month of April.
Snowmelt Trends
Overall, snowmelt volumes during the month of April were higher than the 50% forecast issued on April 1st. Below is the monthly probability volumetric forecast issued on April 1st for the Yuba River at Englebright.
The 50% April volume forecast was 323 TAF on April 1st. If we combine the observed volume with the remaining April forecast volume, we get 367 TAF. The May volume forecast has come down from 365 TAF issued on April 1st to 346 TAF (as of today’s forecast).
The same trend has been observed in the Southern Sierra. The 50% April volume forecast issued on April 1st was 231 TAF (see below). Combining the observed April volume with the residual April forecast gives us 337 TAF. As a result, the 50% forecasted May volumes have dropped from 518 TAF to 466 TAF.
May Outlook
Overall, the first half of May is looking like below normal to near normal temperatures. The week 3-4 range is looking like slight chances of above normal for the Northern Sierra and near to below normal for the Southern Sierra. If this holds true, this should help moderate the snowmelt rates during the month of May. Peak snowmelt week is expected to be anywhere from May 15th to May 30th for much of the Southern Sierra.
Summary
There has been some variability in the monthly runoff volume forecasts through the first part of the April-July snowmelt season, but there has not been a lot of fluctuation in the overall AJ volumes for this “abnormally normal” year. The last time we had a near normal year like this for the San Joaquin was back in the late 1990s.
