A drier than normal January is contributing to February’s lower Columbia River basin water supply forecasts for the months ahead. As was the case in early January, snow water content and water supplies vary throughout the region, but, overall, all are lower than a month ago, according to a NOAA Northwest River Forecast Center water supply briefing this week.
However, as dry as January was, early February precipitation and cold weather in many of the areas offered some hope that snowpack and water supplies could improve this month, particularly in the southern basin.
For the next 10 days, the Northwest River Forecast Center is predicting precipitation in the southern portions of the Columbia basin – east of the Cascade Mountains to eastern Idaho and north towards Yakima and the Tri-Cities that is 125 percent to 175 percent higher than normal. That drops to near normal in a slim band just north of that area and to 50 to 75 percent of normal in a swath across Washington, northern Idaho and southwest Montana. British Columbia precipitation is predicted at below 50 percent of normal for the next 10 days.
In its early January briefing, the NWRFC said that the 2025 water year got off to a slow start due to a below normal April to September 2024 runoff in the northern portions of the basin. That continued with a dry but cool January, dampening river runoff and water supplies throughout the basin in February.
While there is a mix of conditions across the basin, there is a clear distinction between the northern basin where snowpack and water supplies are lower than normal, and the southern areas, where they are generally higher than normal, said Henry Pai, senior hydrologist at the NWRFC, during his online presentation, Thursday, February 6. Still, he added, it is difficult to find any improvement across the basin when looking at water year runoff and water supply forecasts.
Runoff and water supply are largely the same, but with a timing difference. Runoff measures what has been observed during the water year Oct. 1 and, in this case, ending Feb. 5. It is not a forecast since it has already happened. Water supply is a forecast for a supply of water the region can expect in the future.
Pai pointed to runoff in the Canadian portion of the basin where at Mica Dam, runoff water year to date is 123 percent of normal, but that is lower by 6 percentage points than it was in early January. Duncan is at 124 percent of normal, also down 6 percentage points.
Water supply forecasts can be vastly different than water runoff, especially this year. The February water supply forecast at Mica for April through September is 80 percent of normal, down 5 percentage points from the January water supply forecast, which was also the first of the year. For Duncan, the water supply forecast is 80 percent of normal, down 7 percentage points.
Further downstream and in U.S. waters, runoff is even lower, with Libby Dam in Northwest Montana on the Kootenai River at 84 percent of normal, down 5 percentage points, Hungry Horse Dam on the South Fork of the Flathead River, also in Montana, at 60 percent of normal, down 1 percentage point, and Grand Coulee Dam on the mainstem Columbia River at 84 percent of normal, down 7 percentage points.
The February water supply forecast for Libby Dam April through September is 4.72 MAF, 73 percent of normal, down 10 percentage points from the January forecast. The Hungry Horse forecast is at 1.67 MAF, 76 percent of normal, down 7 percentage points, and at Grand Coulee Dam, the forecast is 82 percent, down 6 percentage points.
In the Snake River, year to date runoff at American Falls is at 83 percent of normal, the same as it was in January. Lower Granite Dam is 79 percent of normal, down 3 percentage points and Dworshak is at 72 percent, down 8 percentage points.
Much of this can be explained by changes in the Idaho snowpack, which has dropped from January’s amounts, according to the Natural Resources Conservation Service in Idaho (https://www.nrcs.usda.gov/idaho/snow-survey?utm_medium=email&utm_source=govdelivery).
“Thanks to an abnormally dry January, snowpack percentages compared to normal decreased significantly. said Erin Whorton, Water Supply Specialist for NRCS Idaho. “As of February 1, basin-wide snowpack percentages range from 68 to 119%. This means that snow drought conditions developed in the Wood, Lost, Upper Snake, Bear, Salmon, Clearwater and Coeur d’Alene-St. Joe basins during January.”
“In terms of total water year precipitation, conditions are driest in the Wood and Lost basins (62% to 76%) and wettest along the southern border of Idaho (82 to 97%). Fortunately, at report time, significant snowfall is occurring across the state. Hopefully, these storms will alleviate snow drought conditions.”
The good news is that February water supply forecasts at Snake River dams for April-September are higher. At American Falls the forecast is at 94 percent of normal, up 21 percentage points, and at Lower Granite the forecast is 22.512 MAF, 101 percent of normal, up 7 percentage points, and at Dworshak Dam the forecast is 2.354 MAF, 90 percent of normal, up 1 percentage point.
The culmination of all water available upstream in the Columbia and Snake rivers is measured at The Dalles Dam where the water year runoff is 82 percent of normal. That’s down 6 percentage points and lower than Grand Coulee’s water year runoff at 84 percent of normal. Pei said that’s because water coming out of the Washington Cascade Mountains is so low. For example, the Methow River water year runoff is at a low 65 percent of normal, although that is up 2 percentage points. The Yakima River is at 51 percent of normal, down 3 percentage points and the Walla Walla River is at 66 percent of normal, down 16 percentage points.
The Dalles Dam February water supply forecast is at 79.96 MAF, 85 percent of normal, down 3 percentage points, and slightly higher than at Coulee. The water supply forecast for the Methow River is at 50 percent of normal, down 10 percentage points. The Yakima River water supply is at 99 percent, down 2 percentage points, and the Walla Walla River is at 78 percent of normal, down 12 percentage points from the January water supply forecast.
Even areas where snow water equivalent has been high this year saw a drop during January and that is now reflected in the February water year runoff. The Umatilla River water year runoff is 101 percent of normal, but that’s down 30 percentage points from January’s runoff. The Grande Ronde is 83 of normal, down 9 percentage points, the Owyhee water year runoff is at 109 percent, down 16 percentage points, and the Crooked River is at 188 percent of normal, but that has dropped 66 percentage points since early January.
Unlike water year runoff where runoff is dropping, water supply is rising in the Umatilla River where it is at 104 percent of normal, up 4 percentage points higher than early January. Likewise, the Grande Ronde River water supply is up at 104 percent of normal, 4 percentage points higher, the Owyhee water supply is at 115 percent of normal, up 28 percentage points, and the Crooked River is at 194 percent of normal, a huge gain in one month with a 75-percentage point rise.
Water Supply information is here: https://public.crohms.org/tmt/documents/WSF/WSF_WY25_02.pdf
For background, see:
— CBB, January 20, 2025, Columbia River Basin snowpack a mixed bag so far, water supply forecast at Dalles Dam (April-August) now 89 percent of normal, https://columbiabasinbulletin.org/columbia-river-basin-snowpack-a-mixed-bag-so-far-water-supply-forecast-at-dalles-dam-april-august-now-89-percent-of-normal/
— CBB, June 21, 2024, Basin summer water supply? Record low snowpacks in the north, above normal Southern Idaho, Dalles Dam runoff 77 percent of average, https://columbiabasinbulletin.org/basin-summer-water-supply-record-low-snowpacks-in-the-north-above-normal-southern-idaho-dalles-dam-runoff-77-percent-of-average/