Whether Flathead Lake reaches its summer pool elevation by June 15 will depend on how much rain falls in the valley over the next two weeks.

Each winter, the lake level is lowered by about 10 feet to prevent ice from damaging docks and other infrastructure around the lake.

Snowmelt and precipitation during late spring and early summer is then held back by Kerr Dam, bringing the lake’s elevation up to levels specified in the dam’s Federal Energy Regulatory Commission license.

However, a spokesman for Northwest Energy, which took over dam operations last November, said the company has notified the federal energy agency that this year’s unusually dry conditions and early snowmelt might prevent the lake from reaching full pool by that deadline.

“It’s obviously been very dry in the Flathead this spring, and our flows into Flathead and Kerr Dam actually peaked in March, when typically they would peak much later,” Butch Larcombe said. “Historically, May and June in the Flathead have been pretty wet periods, so if we saw a return to a more normal pattern we might see the full pool levels return.”

As of last Friday, Larcombe said, the lake was about 2.5 feet below the June 15 target of 2,893 feet. With warmer-than-average weather persisting since February, remaining snowpack in the Flathead River Basin is at just 42 percent of normal for this time of year, according to data from automated snow measurement sites.

On top of an early peak melt, Kalispell registered just a fraction of its average rainfall last month, setting a new record for the driest May on record.

June, traditionally the wettest month of the year, started out with rains totaling half inch to an inch across Northwest Montana.

The last time Flathead Lake failed to reach full pool by June 15 was 2001, which held the previous record for the driest May at 0.23 inches.  

Chuck Orwig, a hydrologist with the Northwest River Forecast Center, said the recent rainfall appeared to have improved forecasts for the lake’s elevations but still depends on whether June stays true to historic weather patterns.

“For the last 24 hours, the rise today for the North Fork, Middle Fork and the Hungry Horse outflow, they’re all showing a forecast rise with the rain coming in,” Orwig said Tuesday. “In today’s picture, the Corps has [forecast] the pool getting up to 2,892.85 by about the eighth of June, based on projected precipitation and temperatures for the next 10 days.”

That’s just below the target level, but the forecast is based on historic rainfall patterns for the month. With upper-elevation snow melting early, water flowing into Flathead Lake will be more dependent than normal on new precipitation. Using historic rainfall levels, the river forecast center predicts 65 percent of the lake’s average inflow for the month of June, followed by 60 percent for July.

The two other major reservoirs in the area are also below normal pool elevations, with dam operators adjusting outflows based on stream forecasts.

Eric Edwardson is the operations project manager at Libby Dam, which is run by the Army Corps of Engineers. He said the Corps typically releases two pulses of water downstream to encourage threatened sturgeon to swim upstream to breed. This year, however, low precipitation and early snowmelt forced the agency to curtail that to a single release of water.

“Low-lying snow melts earlier and causes a rush of water, then later on when the higher-elevation melts off, we release a second pulse,” Edwardson said. “We also control the temperature by manipulating gates to draw different water temperatures that trigger the sturgeon to start spawning.”

The dam, which created Lake Kookanusa, is also responsible for contributing approximately 30 percent of the water in the lower Columbia Basin, an important spawning ground for salmon.

Orwig estimated that the Kootenai drainage still has between 40 and 50 percent of its normal snowpack. Edwardson noted the basin has a significant snow deficit but precipitation in June would be the main driver.

“The rainfall, if it comes late in the season in June, you can’t plan for that and empty the water in the lake in a month’s time,” he said. “That’s what got us in trouble two years ago, when we had record-setting rains in June, and by then we had already set up for the releases.”

Hungry Horse Dam, which is operated by the U.S. Bureau of Reclamation, is faring somewhat better, according to Mary Mellema, a hydrologist with the bureau. Hungry Horse Reservoir is currently at about 3,543 feet. Full pool is 3,560 feet.

“We’re still on track to get pretty close to full. We’re expecting runoff to get us within the top five feet,” Mellema said.

The dam is still discharging water at levels above the minimum, however, in anticipation of flow increases to start July 1. Those higher flows are implemented until the end of September to encourage bull trout in the main Flathead River to begin migrating upstream to spawn.

“You don’t want to lower discharges to minimum, and then bring them back up, because it’s very bad for the fish in the mainstem of the Flathead,” she said.

As with the Libby Dam, operators also release extra water to maintain minimum flows in the lower Columbia River, which are necessary for salmon to spawn. With Washington having a particularly dry year so far, Mellema said she expects the levels will be drawn down an additional 20 feet for salmon, compared to a 10-foot drawdown during wet years.

Unlike Kerr Dam, Hungry Horse Reservoir doesn’t have a minimum pool elevation in the winter, instead drawing water levels down for flood control. She added that this winter the reservoir was lowered between 40 and 50 feet below the maximum level to offset the year’s early snowmelt.

“During the winter, if it’s a flood control year we have to draft it down pretty deeply when there’s a lot of runoff,” Mellema said. “But by the end of June, we’re going to be at fairly normal levels in the reservoir.”

That could bode well for Flathead Lake as well. Larcombe noted that extra water released from Hungry Horse Reservoir could make the difference in reaching its minimum pool level.

“The weather is a big factor, and the other is the operation of Hungry Horse Dam, which we don’t own or operate,” he said. “So we’re sort of at their mercy to some degree as well.”

Reporter Samuel Wilson can be reached at 758-4407 or by email at swilson@dailyinterlake.com