Dry March pulls down water supply forecast across the Pacific Northwest

New York — The Dalles Dam water supply forecast has dropped to its lowest point since December 2020 as inflows sit well below the three-year average, with the weather forecast showing below-normal precipitation and power forwards trending as much as 136% higher than a year earlier.

The Dallas water supply forecast is at 91% of normal for the April-September forecast period, down 5 percentage points from the end of February, according to Northwest River Forecast Center data. The forecast reached a high of 108% in November 2020.

"March was dry and as a result precipitation was down with the volume forecast was down," hydrometeorologist Ryan Lucas said during the April 1 Northwest River Forecast Center water supply briefing. "Fortunately, March was cooler and allowed snow in the mountains to stay there."

While there was steady snow building over the course of the year, that flatlined in March with a lack of precipitation, Lucas said. As a result, snowpack for the Columbia River above The Dalles is at 79% of normal, down 8 percentage points month on month.

Inflows at The Dalles dropped 18.5% month on month to average 120 kcfs in March, down about 4% year on year, according to the US Army Corps of Engineers data. Less inflows into the reservoir caused generation produced at The Dalles to drop 25% month on month to an average of 711 MW for March 1-23, down 4.4% year on year.

"There is some precipitation in the forecast, which is good, but the development we see over the next 10 days is pretty dry compared to what we see as normal," Lucas said, adding the dry March pulled down the water supply forecast.

The 10-day precipitation forecast a normal to above-normal precipitation probability, according to the US National Weather Service.

Price impact

The three-month outlook is mixed, with chances for below-normal precipitation and equal chances for above- and below-normal precipitation across the region, according to NWS. Temperatures have greater chances for below-normal temperatures in the three-month outlook.

Precipitation leads to snowpack, which translates into hydropower generation once the runoff season starts and that impacts wholesale power prices.

With less snowpack, Mid-C power forwards have spiked above year-ago counterparts as less hydropower or renewable generation tends to drive up power prices.

Mid-C on-peak July averaged $43.25/MWh in March, climbing as high as $69/MWh by the end of the month, a package high and 116% above the year-ago package, according to S&P Global Platts.

Likewise, on-peak August climbed to $94/MWh March 31, also a package high and 136% higher than the 2020 package a year ago.

For comparison, Mid-C on-peak day-ahead prices in July 2020 averaged $19.26/MWh and August 2020 averaged $37.07/MWh, according to Platts pricing data.