Delayed warmer weather kicks off US Northwest snowmelt, boosts hydro outlook

Despite below-normal precipitation throughout the current water year, much colder winter weather resulted in healthy snowpacks across the Columbia River Basin, which translates into stronger hydro supply outlooks than just a year ago when drought threatened the western US.

However, water-year-to-date adjusted runoff levels are still below normal with the spring snowmelt season just now starting, a delay compared to years past, Geoffrey Walters, lead hydrologist with the Northwest River Forecast Center, said during the May 4 water supply briefing. Typically, November through March are the wettest months.

"May can change the outlook of the water supply forecast if we have a wetter or drier month," Walters said.

Improvements in hydro supply have pulled down power forwards across the region. Mid-C on-peak June is currently in the mid-$40s/MWh, $23 lower than a month ago, according to data from Platts, a division of S&P Global Commodity Insights. Meanwhile, SP15 on-peak June is in the upper $40s/MWh, more than $4 lower than a month ago, while Palo Verde on-peak June is in the mid-$70s/MWh, more than $11 lower than in early April.

Weather changes

"Precipitation has been below normal through the winter and pretty much through the water supply year," Walters said. "But, because of the cold temperatures, we've actually has pretty decent snowpack levels."

Snowpack levels are near normal despite below-normal precipitation.

Water year precipitation at Grand Coulee Dam is 72% of normal, which is below the 30-year average level but consistent with recent years, Walters said. At the Lower Granite Dam, water year precipitation is 87% of normal, while at The Dalles Dam it is 78% of normal.

"Last week there was a change in the weather pattern ... and rivers have responded," Walters said. "That's led to a dramatic turnaround in basin conditions."

Warmer spring temperatures have caused snow to start melting and river levels to rise. However, runoff levels are still below normal.

The Dalles water-year-to-date adjusted runoff is at 61% of normal, up 5 percentage points from a month ago, while Grand Coulee is at 59%, up 4 points, Walters said.

The Dalles is the traditional index for the entire Columbia River system.

The Dalles Dam

The water supply forecast at The Dalles Dam, located on the Columbia River separating Oregon and Washington, is currently at 93% of normal for the April-September forecast period, up seven points month on month, but down 2 points year on year, according to NWRFC data. The water supply forecast year runs Oct. 1 through Sept. 30.

Inflows at The Dalles were down 10% year on year to average 125.39 thousand cubic feet per second (kcfs) in April, according to US Army Corps of Engineers data. That's an improvement from being down 37% year on year in March.

Generation at The Dalles averaged nearly 492 MW in April, down 15% year on year, which is an improvement from 36% lower year on year in March, according to Corps of Engineers data.

Conditions at The Dalles serve as the barometer for hydro conditions in the region and indicate any potential surplus energy for exports into neighboring regions. Less hydro generation in the Pacific Northwest translates to less generation available for exports to neighboring regions.

Hydro generation

Northwest hydro market share was down 5 percentage points year on year in April to average about 62% of the total fuel mix, according to Bonneville Power Administrator data. However, BPA hydro has climbed in recent days, averaging 11% higher year on year so far in May.

"Over the past week, northwest hydro output has increased by about 8 aGW," said Morris Greenberg, senior manager with the low-carbon electricity team at S&P Global Commodity Insights. "This has reversed the direction of energy flow on a daily average basis to California."

California Independent System Operator imports averaged 3% of the total fuel mix in April, a decrease of nearly 14 points from a year ago, according to California Independent System Operator data. On nearly half the days in April, CAISO was actually exporting power instead of receiving generation imports.

At the same time, CAISO hydro market share averaged over 15% of the total fuel mix, up 7.5 points from a year ago.

Across the West

There have been major improvements during the past few months across California and the Great Basin, but little or no precipitation in the last week, according to the US Drought Monitor. Farther North, drought of varying intensity is designated for parts of Oregon and northern Idaho where precipitation has averaged below normal so far this water year.

The water supply forecast at Shasta Dam in Northern California is currently at 137% of mean for the April-July forecast period, down 13 points month on month, according to California Nevada River Forecast Center data.

Meanwhile, the water supply forecast at Glen Canyon Dam on the Arizona-Utah border is 172% of average for the April-July forecast period, down 5 points month on month, according to Colorado Basin River Forecast Center data.