It appears the tables have turned for early precipitation in the Big Lost basin, according to Danny Tappa, hydrologist with the Natural Resources Conservation Service.
In the Jan. 1 water supply outlook report, Tappa wrote that the Big Lost basin “had a very difficult go last year. The word dry barely does it justice. In fact, the past few years have not been kind to the Big Lost.”
Through Jan. 4, when the survey data was collected, snow water equivalent in the Big Lost basin stood at 9.3 inches, an “impressive 154 percent of normal,” the snow survey states. Snow water equivalent in the basin generally peaks at 12.9 inches in early April. “We are well on our way there,” he said. Winter precipitation usually hits the basin through April and, if the trend continues, it means good news.
Throughout Idaho fall precipitation and late December snowstorms brought relief to drought conditions, Tappa and other NCRS staffers wrote. They caution that “we’re not out of the woods yet.” But drought severity is reduced and soil moisture and shallow groundwater sources improved throughout the fall. Those factors, coupled with above-normal December snowfall “provide more optimism for more efficient runoff come spring,” the report states.
NRCS personnel estimate Idaho needs to get between 135 and 190 percent of normal precipitation this winter to end drought conditions by April 1. That means the probability of improving drought conditions is higher than of ending drought conditions.
The highest percent of normal snowpack in the state is currently recorded in the Wood and Lost River basins. Those two basins have between 130 and 150 percent of normal snowpack so far, “a welcome departure from having the worst drought conditions in the state over the last two years,” Tappa wrote. The two basins are already near or above their snowpack and snow water equivalent peaks from last winter.
Reservoir storage in the Wood and Lost basins ranges from 40 to 65 percent of normal. Mackay Reservoir is at 66 percent of normal while the Little Wood Reservoir is at 61 percent of normal and Magic Reservoir was at 39 percent of normal on Jan. 4.
Snowpack density ranges from 18 to 24 percent across the two basins. Soil moisture values are above normal, which are expected to increase spring runoff efficiency.
Snowpack is off to a good start in the Salmon River basin, the report states. Precipitation was 115 percent of normal as of Jan. 1 with slightly higher amounts in the southern sub basins. December storms brought the snowpack from 30-year lows on Dec. 11 to 117 percent of normal on Jan. 1. Bulk snowpack density at snotel sites is “remarkably uniform across the basin, ranging from 20 to 25 percent,” Tappa reported.
Snowpack across Idaho was alarmingly low until mid-December, the report states. Snowpack is now above normal in all basins north of the Snake River Plain and below or near normal in the southern Snake basins.
October storms brought wet conditions and above-normal precipitation to all of Idaho except the Clearwater basin. Snow fell at higher elevations in parts of Central Idaho in October, but most of the precipitation that month came as rain because of warmer-than-normal temperatures, the report states. November was significantly warmer than normal across all of Idaho. Combined with a lack of precipitation, early snowpack development was delayed.
Forecasts for January from NOAA’s climate prediction center “suggest increased odds of above-normal precipitation and cooler than average temperatures” across the Gem state. Northern Idaho should especially benefit from cooler and wetter La Niña conditions. NOAA’s three-month outlook predicts equal chances for warm, neutral or cooler conditions in the southern Snake River and Snake River headwaters basins. That means reservoir storage along the Snake could still be an issue since carryover this fall was well below normal, Tappa wrote.
Streamflow forecasts anticipate near-normal conditions from April through July throughout the state.