Published 11:15 am Tuesday, April 9, 2024
Winter weather has left northern Idaho with one of its lowest snowpacks on record and southern Idaho with one of its biggest snowpacks for a second year in a row, according to the Natural Resources Conservation Service in Idaho.
Everywhere south of the Salmon Basin has had a pretty good winter in terms of snowpack, said Erin Whorton, water supply specialist for NRCS Idaho.
“Southern Idaho got tons of precipitation. It’s been really wet this year down there for the second year in a row. So water supply looks really good in southern Idaho,” she said.
For the Boise Basin, Little Wood, Big Wood and Lost basins and the upper Snake River above Milner Dam, it’s shaping up to be a good water year, with nearly normal snowpack and higher reservoir storage, she said.
Folks who rely on Mackay Reservoir are probably going to be challenged, as the reservoir is filling after repairs. But snowpack is good, so hopefully it will fill, she said.
“Northern Idaho down to the Salmon basin had another low snowpack year. That means there will probably be a reduced amount of water in streams and rivers compared with normal,” she said.
Water supply looks sufficient this season, especially for users with ample storage rights, although the impacts of a low snow year will be felt in northern Idaho, she said.
March was a wet month with near- to above-normal precipitation across the state. Southern and eastern Idaho were the wettest, with northern Idaho remaining drier than the rest of the state. Total monthly precipitation during March ranged from 89% of normal monthly precipitation in the Coeur d’Alene-St. Joe basin to 183% in the Oakley basin.
Another month of improvements in Idaho’s snowpack boosted confidence in water supply for the upcoming season. Reservoir storage was at or above normal on April 1 with the exception of Mackay Reservoir, Brownlee and Lake Pend Orielle.
In general, reservoir storage this water year is greater than storage levels at this time during Water Year 2021, the last water year with above-normal storage at the beginning of the irrigation season.
The Boise River system had storage at 123% of normal on April 1. Snowpack in the Boise system is much higher than other west central basins, the agency reported.
Reservoir storage in the Payette River system is 108% of normal. However, snowpack is only 79% of peak snow water equivalent on April 1, which could prevent Deadwood Reservoir from filling. Cascade Reservoir will likely fill.
Total storage in the Upper Snake Reservoir system above Milner Dam was about 120% of normal on April 1. Combined Jackson Lake and Palisades storage above Heise was 134% of normal.
Streamflow forecasts across Idaho remain sharply divided between the north and south. Above-normal streamflow is expected in southern Idaho and well below-normal streamflow is expected in central and northern Idaho. Nearly normal streamflow is expected in the Wood and Lost basins as well as the Henrys Fork-Teton Basin.
Streamflow, snowpack, and precipitation data for each basin are available on the Idaho Snow Survey website.
