Rain-Heavy Precipitation Mix Concerns Idaho Water Supply Forecasters
Idaho and much of the West are experiencing a snow drought, posing a threat to water supplies for irrigation and other uses.Despite above-normal precipitation this winter,warmer-than-normal temperatures have resulted in rain rather of snow,notably at lower elevations.
idaho and the western Snow Drought
A concerning lag in snowpack is developing in Idaho as we reach the midpoint of the snow accumulation season.According to hydrologists at the USDA Natural Resources Conservation service (NRCS), this situation threatens the availability of water for irrigation and other crucial needs later in the year.
“The Western U.S. and most of Idaho are in a snow drought thanks to warmer than normal temperatures in November, December and the beginning of January,” NRCS Idaho water supply specialist Erin Whorton said in a news release. “Even though Idaho received above-normal precipitation this winter thus far, with high-temperature records being set everywhere, only the highest mountain ranges have gotten more snow than rain.”
this “snow drought” isn’t necessarily a lack of precipitation,but rather temperatures that are too high for precipitation to fall as snow. The NRCS-Idaho’s January water supply outlook report highlights this unusual situation: “This brings us to the unusual situation where total water year precipitation is near or above normal in all Idaho basins, but the snowpack is abysmally low across large swaths of the state.”
While recent atmospheric river storms have helped alleviate drought severity in some areas, the underlying warm conditions persist. “If the snowpack continues to lag behind, the long-term accumulated precipitation deficits could have substantial negative impacts on water supply in Idaho.”
The water year began with warm and wet conditions, preventing snow accumulation except at the highest elevations. Snowpack levels in most Idaho river basins were at or near record lows until mid-December.
Current Snowpack Status
Currently, the Salmon River basin in north-central Idaho, along with the Wood and Lost basins in the central mountains, and the Upper Snake basin above Heise in the east, have snowpack near or above normal. However, basins in northern Idaho, the west-central mountains, and the southern Snake River Plain “remain well below normal, and many sites are at historic lows.”
The exceptions are the Wood, Lost, and Snake headwater basins, which are showing positive signs.
“But even in those basins, the lower valleys are devoid of snow for the first time in many people’s memory,” the report said.“Water supply concerns diverge across Idaho depending on each basin’s particular combination of reservoir storage and snowpack status.”
Statewide snowpack is currently 88% of normal. Normally, at this time of year, Idaho’s snowpack should be around 50% of its peak annual accumulation; it is currently at 42%.
Snowpack typically peaks around April 1.
Most of Idaho is experiencing below-normal snowpack, especially areas south of the Snake River.
Reservoir levels are mixed: 112% of normal on the Boise River,80% in the Upper Snake,and 184% in the Owyhee basin,which has seen above-normal snowpack for three years but currently sits at around 15% of normal. The Owyhee Reservoir holds a roughly two-season supply of irrigation water.
The Role of La Niña
the current La Niña weather pattern typically brings cooler temperatures and increased precipitation to the Pacific Northwest.
“We have received the precipitation but not the cool temperatures that typically deliver an above normal snowpack,” the report states.
The National Weather Service Climate Prediction Centre forecasts cooler-than-normal temperatures for February-April in Idaho’s northern panhandle and wetter-than-normal conditions north of the Snake River Plain. Conversely, warmer and drier conditions are predicted for April-June statewide.
“Last year, these dry and hot spring conditions led to rapid snowmelt, reduced runoff from the snowpack and earlier irrigation demand which stressed water supplies,” the NRCS Idaho report said.
