October brings a foot of rainfall to area mountains

Already the wettest October on record for most of Northwest Montana, last month wrapped up as Kalispell’s sixth-rainiest month of all time and broke the overall records for single-month precipitation in several nearby towns.

The rain gauge at Hungry Horse Dam became the first in the region to record more than a foot of rain in a single month, with 12.3 inches of total precipitation. That bested the previous record of 10.8 inches, recorded in November 1973.

West Glacier recorded 10.6 inches — its wettest month since 1948, when records for the weather station begin. More than 8 inches of rain in Troy broke the town’s single-month record, which was also set in November 1973.

In the Flathead Valley, rainfall totals were less impressive, but the 4.86 inches of October precipitation at Glacier Park International Airport still gave Kalispell its rainiest October, easily breaking the 1914 record of 3.4 inches. According to historical data from the National Weather Service, October averages just 1.01 inches, making it typically the third-driest month of the year.

Corby Dickerson, a meteorologist at the National Weather Service office in Missoula, said the unusual month owed much to the outgoing El Nino weather system, which generated a high number of powerful West Pacific typhoons last month. Typhoon season averages three to four named typhoons, he said, but five of the massive storm systems developed in October alone, plus one that had fizzled out by the end of September.

“That moisture from the six storms kept getting entrained into the upper level of the jet stream,” he said. “We call them ‘atmospheric river events,’ and they typically carry a lot of tropical moisture with them.”

The consistent push of typhoon leftovers into the United States’ Pacific Northwest delivered the month’s seemingly unending procession of rainy days. On all but six days last month, Kalispell received measurable precipitation. Despite the impressive monthly total, only the Oct. 9 single-day record was broken, when 0.68 inches of rain fell at the airport weather station.

Rivers and creeks throughout the region are running at record highs for this time of the year, with flow rates more typical of springtime numbers.

Gauges at West Glacier and Columbia Falls showed the Middle and North forks of the Flathead River have broken several long-standing records for single-day flows through the second half of October, although water levels remain well below flood stage.

The swollen waterways have stymied the typical draw-down of Flathead Lake, which on Tuesday remained within a half-foot of full pool. Energy Keepers, Inc., a tribally owned corporation that operates Séliš Ksanka Ql’ispé Dam, is bound by its federal energy license to keep the surface at 2,893 feet during the summer. Beginning in the fall, water is gradually let out to lower the elevation to 2,883 feet by April 15.

“Those are just absolutely staggering streamflow and precipitation totals,” Travis Togo, Energy Keepers’ director of power management, said Tuesday.

He added that the Flathead River basin as a whole received more than 300 percent of its normal precipitation last month.

“When you look at this October that just happened, we had 738,000 acre-feet of water,” Togo said, referring to the amount flowing into the lake. “It’s very similar to April, which would normally be one of our three wettest months of the year.”

A typical October, he said, would see 223,000 acre-feet of water flowing into the lake. The difference equates to an additional 3 to 4 feet of lake elevation.

Dam operators had brought water levels slightly below average by the start of the month. Togo said that draw-down continued until about mid-October, after which the lake elevation began marching back up to its current level, about a third of a foot below full pool.

He didn’t expect to have any difficulty bringing the annual draw-down back on schedule in the coming months. From a business standpoint, he added, the month’s odd weather was a boon.

“Not surprisingly, we generated a lot more electricity in October than we would have in a normal October,” Togo said.

The dam averaged 120 megawatts of power throughout the month, he said, compared with its October average of 87 megawatts.

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