This La Niña winter proved to be drier than hoped for across much of Idaho. Except for the Clearwater Basin, the lack of precipitation during March resulted in near to below normal snowpack across Idaho as of April 1. Across the state, current reservoir storage is on pace with the historical 30-year average storage level, indicating normal winter baseflow into reservoirs.
“Dry conditions in the Wood and Lost basin indicate water supply concerns for irrigators, dryland grazing operations and folks relying on natural streamflow,” said Erin Whorton, Hydrologist-Water Supply Specialist for NRCS Snow Survey in Idaho. “There will likely be agricultural water shortages in these basins this summer. In addition, dry conditions in the Bear River Basin are of concern for ranchers using non-irrigated pastures for forage, however, reservoir storage in that basin appears sufficient for irrigators. Drought conditions in central and southern Idaho are expected to persist during spring. Across the Snake River basins, except for Oakley and Salmon Falls, we expect sufficient reservoir supply for irrigators. At report time, we also expect normal irrigation water supply across the rest of Idaho.”
Current SNOTEL data indicates that peak snowpack has been reached this winter and the melt season has begun in earnest below the high elevation sites. Once the snowpack reaches 32°F throughout its entire thickness it’s considered isothermal. When the snowpack reaches this point, runoff from snowmelt begins. Cold snaps can temporarily slow down snowmelt, but once the snowpack is isothermal, winter is over, and spring is here to stay. These are the conditions Snow Survey is observing across Idaho.
Streamflow, snowpack, and precipitation data for each basin can be accessed on the NRCS Idaho Snow Survey web page.
For information on specific basins, streams, and reservoirs, please view the full report online at April Water Supply Outlook Report.