Columbia Basin Water Supply Forecast Still Projected Well Below Normal; Expect Early Runoff, Lower Flows This Spring/Summer

Water supply forecasts at major dams in the Columbia River basin dropped again during March, with the forecast at The Dalles Dam dropping from 83 percent of normal in February to 80 percent of normal in March, according to the April 3 water supply forecast by NOAA’s Northwest River Forecast Center.

However, not all of the basin’s water supplies are as far below average. Higher than normal snowfall in southern Idaho and northeast Oregon are elevating the upper Snake River basin water supplies, where at American Falls the water supply, April – Sept., is 115 percent (3 percent lower than the March forecast) and at Lucky Peak it is at 94 percent (9 percent lower than the March forecast), according to a NOAA NWRFC presentation by Henry Pai this week.

Unfortunately, by the time the water reaches Lower Granite Dam on the lower Snake River and Clearwater River water supply is factored in, the forecast drops to 89 percent of normal, still higher by 2 percentage points than the March forecast.

Pai said that lack of precipitation upstream of The Dalles Dam is driving the lower-than-normal forecasts throughout the basin.

Although southern Idaho has received higher than normal snowfall this year, the north side of Idaho and the Clearwater River basin have not, leaving Dworshak Dam on the North Fork of the Clearwater River at 76 percent of normal, down 1 percentage point from the March forecast.

Willow Walker of the U.S. Army Corps of Engineers’ Walla Walla District said this week at an interagency Technical Management Team meeting that Dworshak is still likely to meet its April refill target, but it may have to do so by sustaining minimum outflows through April. That could impact releases of juveniles at Clearwater hatcheries, Jay Hesse, Nez Perce Tribe, said at the TMT meeting. A full reservoir by the end of April is important to provide cold water flow augmentation in late spring and summer targeting out-migrating juvenile salmon at Lower Granite Dam in the lower Snake River.

According to Pai, of the 76-year history of recording water supplies throughout the basin, this is the worst year for Mica Dam in British Columbia where the April 3 forecast is 77 percent of normal, down a full 5 percentage points from the previous month. That upper basin lack of water is driving down the water supply at Grand Coulee Dam to 81 percent of normal, down 2 percentage points from last month.

In addition, the Clearwater River basin, which includes Dworshak Dam, is in its 20^th driest year out of the 76 years of record-keeping.

On the other hand, the Owyhee River basin is at its second highest of the 76-year history.

Further east, Montana is experiencing very low snowpack and lower than normal water supply expectations. Libby Dam water supply is at 81 percent of normal, actually up 2 percentage points from the March forecast. And, Hungry Horse Dam water supply is at 75 percent of normal, up 1 percentage point.

Snowpack varies throughout the basin, according to Pai. High snow levels, in some cases in the mid-200 percent of average range, persist in southern Idaho and NE Oregon. Pai said that there is too much water for that area and that NOAA has flood concerns. Libby is lower than normal. The southern Washington Cascade Mountain snowpack is generally close to normal, although much of the low-level snow has melted.

Snowpack in the Columbia River basin upstream of Grand Coulee is 80 percent of normal and higher than last year at this time. Snowpack in the Snake River basin is near normal and higher than during the past two years, Pai said. It is higher in the south and lower in the north.

Runoff at Grand Coulee is expected to be 94 percent of normal, 74 percent at Mica, 72 percent at Dworshak, 80 percent at Lower Granite, 85 percent at The Dalles, 135 percent at the Methow River, 84 percent at Yakima, 102 percent at the Willamette River above Salem, 162 percent at the Crooked River, 111 percent at the Owyhee River, 92 percent at the Grande Ronde River and 94 percent at the Umatilla River.

Pai predicts that runoff at Grand Coulee will be normal in April, but lower in May and June, indicating an early runoff from the upper Columbia River. He predicts higher than average runoff at Lower Granite Dam on the Snake River in April, slightly lower than average runoff in May and lower than average in June.

Wrapping up weather in the first three months of this year, Pai said that January was wet in Oregon and southern Idaho, but most of Washington in the northeast Columbia basin and northern Cascades was dry. In general, temperatures were cooler in the north and warmer in the south.

February precipitation was above normal in most of the basin, with the exception of the Washington Cascades. Temperatures were cooler than normal east of the Cascade Mountains, but with more rain the snow.

March saw a transition to a drier “signal,” Paid said. The exception was southern Idaho and northeast Oregon.

Looking ahead 10 days, Pai said to expect wetter than normal conditions in southern Idaho and northeast Oregon, while Canada, Washington Cascades and south into the Oregon Cascades can expect drier than normal conditions.

More information available here: https://pweb.crohms.org/tmt/documents/WSF/.

NOAA’s Climate Prediction Center’s national weather outlook for spring (April through June) is above average temperatures for most of U.S., wetter in the Southeast, low flood potential likely across the U.S., as drought worsens for parts of the Plains.

“Climate change is affecting the timing, intensity and duration of weather events in the United States,” said NOAA Administrator Rick Spinrad, Ph.D. “The Spring Outlook is one of the many tools NOAA provides to help communities prepare for what’s ahead.”

The greatest chance for above-average temperatures is in the Great Lakes region, the Pacific Northwest and Northwest Alaska, though most of the continental U.S. and Alaska have elevated odds of above-average temperatures, the forecast says.

Parts of the Pacific Northwest and Southwest are most likely to see precipitation below the seasonal average.

There is an 83 percent probability that ENSO Neutral conditions, neither El Nino nor La Nina, will return by the April-May-June 2024 timeframe. However, El Nino is expected to continue impacting weather patterns in the U.S. into the spring. A La Nina Watch issued by the Climate Prediction Center remains in effect — meaning La Nina conditions could return to the equatorial Pacific within six months.

“Our scientists at the Climate Prediction Center observed one of the strongest El Nino events on record during the winter of 2023-2024,” said Jon Gottschalck, chief of the Operational Prediction Branch from NOAA’s Climate Prediction Center. “But a quick transition to La Nina — the cool phase of ENSO — is possible as early as the first part of summer.”

For background, see:

— CBB, March 7, 2024, FEBRUARY’S LOWER TEMPS, NORMAL PRECIP GIVES SLIGHT IMPROVEMENT TO COLUMBIA BASIN APRIL-AUGUST WATER SUPPLY FORECAST; 83 PERCENT OF AVERAGE, https://columbiabasinbulletin.org/februarys-lower-temps-normal-precip-gives-slight-improvement-to-columbia-basin-april-august-water-supply-forecast-83-percent-of-average/

— CBB, February 16, 2024, BASIN WATER SUPPLY DROPPING WITH MOST WATERSHEDS WELL BELOW NORMAL, SETTING UP LOW EXPECTATIONS FOR THE YEAR, https://columbiabasinbulletin.org/basin-water-supply-dropping-with-most-watersheds-well-below-normal-setting-up-low-expectations-for-the-year/

— CBB, January 18, 2024, SEEMS LIKE A LOT OF SNOWY, WET WEATHER, BUT COLUMBIA BASIN WATER SUPPLY LIKELY TO REMAIN BELOW NORMAL; 77 PERCENT AT DALLES DAM, https://columbiabasinbulletin.org/seems-like-a-lot-of-snowy-wet-weather-but-columbia-basin-water-supply-likely-to-remain-below-normal-77-percent-at-dalles-dam/

— CBB, May 10, 2023, BASIN WATER SUPPLY FORECASTS RISING, 93 PERCENT OF NORMAL AT DALLES DAM; LOW CANADA SNOWPACK IMPACTING FLOWS, https://columbiabasinbulletin.org/basin-water-supply-forecasts-rising-93-percent-of-normal-at-dalles-dam-low-canada-snowpack-impacting-flows/

— CBB, April 14, 2023, COOLER WEATHER KEEPING SNOWPACK HIGHER UP BUT BASIN WATER SUPPLY EXPECTED TO BE BELOW AVERAGE THIS SUMMER, https://columbiabasinbulletin.org/cooler-weather-keeping-snowpack-higher-up-but-basin-water-supply-expected-to-be-below-average-this-summer/

— CBB, March 9, 2023, ALL THIS WET WEATHER YET COLUMBIA RIVER BASIN WATER SUPPLY FORECAST FOR SALMON MIGRATING SEASON STILL BELOW NORMAL, https://columbiabasinbulletin.org/all-this-wet-weather-yet-columbia-river-basin-water-supply-forecast-for-salmon-migrating-season-still-below-normal/

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