Dry conditions could prevent full pool in Flathead Lake

A spokesman for Northwest Energy, which took over operations at Kerr Dam last November, recently said the company has notified the  Federal Energy Regulatory Commission that this year’s unusually dry conditions and early snowmelt might prevent Flathead Lake from reaching full pool by June 15.

“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, Flathead 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 how high the lake level will go 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 June 2. “In today’s picture, the Corps has the pool getting up to 2,892.85 by about June 8, 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 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. The 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,” Mellema said. “We’re expecting runoff to get us within the top five feet.”

The Hungry Horse Dam is still discharging water at levels above the minimum in anticipation of flow increases starting July 1. Those higher flows are implemented until the end of September to encourage bull trout in the maintem of the 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,” Mellema said.

Unlike Kerr Dam, the Hungry Horse Reservoir doesn’t have a minimum pool elevation in the winter, instead drawing water levels down for flood control. Mellema 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,” she 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.”