After recent snow and rain storms in February and March, snowpack levels for Eastern Idaho are all over 100% for this time of the year.
In a report from the Idaho Natural Resources Conservation Service, above average precipitation is leading to a positive outlook for the water levels during our growing season.
However, the news isn't that great for Western and South-Central Idaho, with some snowpacks below 100 %. That could lead to water being limited for some users.
Back–to-back months of above average precipitation across most of Idaho boosted the water supply outlook according to the April report released by the Idaho Natural Resources Conservation Service. March precipitation amounts ranged from 103% to 190% of normal.
“The water year started with four dry months from October to January,” said Ron Abramovich, Water Supply Specialist with the Idaho Natural Resources Conservation Service. “The water supply made an amazing recovery due to the February and March precipitation.”
“However, despite good precipitation the last two months we are predicting water shortages in several areas,” said Abramovich. Predicted water supply shortages will occur in the Big Wood, Big Lost, Little Lost, Oakley, Owyhee, and Salmon Falls basins.
Higher elevations accumulated snow while lower elevations got rain. Abramovich notes the mid-elevation snowpack, between 5,000-6,000 feet, was lacking across central Idaho from Weiser in the west to Swan Valley in the east. The mid-elevation snows are important for rangeland and dryland farmers.
As far as streamflow forecasts Abramovich said “the variability across our region is amazing this year.” The lowest predicted streamflows are in the water-starved Owyhee Basin and Camas Creek near Fairfield. Those areas are predicted to have a meager 20% of normal. The best streamflow forecasts are 130-150% of normal in the headwaters of the Upper Snake and Clearwater Rivers.
The report notes that some reservoirs will fill because of adequate snowpack to feed them and others might fill depending on irrigation demand and runoff timing. Reservoirs in the drier parts of the state will not fill. For more details on reservoirs as well as snowpack, precipitation, and streamflow predictions for each basin in Idaho, view the full April Water Supply Outlook Report online.
Below is a summary for each basin:
Bear Basin -- March provided above normal precipitation, which helps maintain the above normal snowpack and the basin’s slightly above average water year-to-date precipitation level. Natural flow water users can expect much better water volumes will be available in the rivers than the past two seasons.
Clearwater Basin -- Consistent winter precipitation this season led to deep snowpacks resulting in well above average streamflow forecasts. Because of the good, consistent weather pattern bringing moisture into this region, water users should consider using the wetter streamflow forecasts.
Salmon Basin – Two months of above average precipitation brought the basin back to near normal water year-to-date precipitation amounts that increased streamflow forecasts.
Southside Snake River Basins (Owyhee, Bruneau, Salmon Falls, Oakley) -- March brought the Southside Snake basins another month of above normal precipitation. However, the Surface Water Supply Index, which combines current reservoir storage with forecasted streamflow, indicates that more wet weather is needed to prevent water shortages.
Upper Snake River Basin -- Despite current below normal storage levels, water users should expect the reservoirs to fill, or nearly fill, depending on the timing of runoff. The Upper Snake’s water supply is in great shape to handle whatever weather this summer may bring.
Weiser, Payette, Boise River Basins -- Most streamflow forecasts range from 90-100% of average, with the only exception being the Weiser River which is forecast at 80%. Managers expect Arrowrock and Lucky Peak reservoirs to fill; Anderson Ranch Reservoir is uncertain at this time. With reservoirs rebounding and good streamflow predicted, water supplies should be adequate to meet demand.
Wood and Lost River Basins – Despite good March precipitation in these basins, water supply shortages are still expected in the Little Lost, Big Wood, and Big Lost areas. Snowpacks very with elevation ranging from 50-100% of normal; water users should plan for shortages and look for ways to improve efficiencies in their irrigation systems.
***This report was provided by Alexis Collins of the NRCS and USDA