Fifty years ago today, the biggest flood on record in Montana began to sweep over the Flathead Valley and communities east of the Continental Divide, the result of a freakish combination of meteorological forces.

A new sign was unveiled last week at the Teakettle fishing access site near Columbia Falls showing the exact level the Flathead River reached when the river crested on June 9, 1964.

The line on the sign, well above the reach of any person, denotes the 25.8-foot level the river reached with flows surging to 176,000 cubic feet per second on June 9, 1964.

By comparison, the Flathead River has been at the 11-foot level recently with flows at 33,000 cfs. Flood stage is 13 feet and 44,000 cfs.

“It’s a sign that Mother Nature can really get out of control,” said National Weather Service hydrologist Ray Nickless, who gave an overview of the turn of events leading to the epic flood.

A low-pressure weather system, common at this of year, was circulating counter-clockwise in northern Wyoming, drawing a system loaded with precipitation from the Gulf of Mexico into the northern Rockies, where it collided with another front moving south from Canada.

The drenching result: Over a 30-hour period, 14 to 16 inches of rain fell on the Continental Divide in what is now the Bob Marshall and Great Bear wilderness areas, causing a flash runoff of mountain snowpack that was well above average.

That’s more precipitation than many Montana communities get in an entire year.

“It was really the rainfall that caused the problem,” Nickless said. “It’s one of those events that can happen over time but it is extremely rare.”

Charles Parrett, a hydrologist who worked for the U.S. Geological Survey for 30 years, gave a lecture Thursday along with his son, Aaron, on the 1964 Flood at Flathead Valley Community College during an event sponsored by the Flathead Conservation District and the Daily Inter Lake.

“The really interesting thing is that [the rainfall] was focused right over the center of the Continental Divide,” he said as he displayed a map showing the tightly concentrated area of heavy rainfall.

That caused catastrophic flooding both east and west of the Divide, inundating the Flathead Valley, Choteau, St. Mary, parts of Great Falls and the Blackfeet Indian Reservation, where 30 people died.

Parrett noted that the largest known flood on the Flathead River prior to 1964 occurred in 1894 when the river peaked at 150,000 cubic feet per second. That’s considerably short of the 176,000-cfs peaks flows of 50 years ago — and the 1894 flood happened before the construction of Hungry Horse Dam.

In 1964, the dam successfully held back high flows from the South Fork Flathead drainage.

If the dam hadn’t existed, Flathead River flows at Columbia Falls during the Flood of ’64 would have reached nearly 250,000 cfs, Parrett said.

The chance of a 1964-magnitude flood recurring twice in a century is considered to be 1 percent every year, said Parrett, who likened that to the chance of drawing a full house two times in a row in a game of poker.

“It’s really rare, but it can happen,” he said.

A lot has changed in terms of forecasting for floods since 1964, Nickless said.

“We do have a lot more information” as the result of high-tech automated snow and rain gauges in the mountains, Nickless said. “We’re more advanced with our atmospheric models also.”

Fifty years ago, there were warnings that could have helped communities far downstream from the Continental Divide, Nickless said.

“But to really convince people that it’s going to be that bad, that’s the hard part,” Nickless said. “You wouldn’t think that all that water is going to come out of those mountains.”

On the Blackfeet Reservation, there was no warning because the flash flooding that killed 30 people was the result of dams on Birch Creek and the Two Medicine River being breached.

Aaron Parrett, an author and professor from the University of Great Falls who has written at length about the flood and the lives lost, remarked about how people tend to recall their lives in terms of events such as the 1964 Flood.

“People think about their lives in terms of their memories of meteorological events,” he told the standing-room-only crowd at the college’s large conference room. “People tend to date their histories in terms of these events.”

The big flood is the subject of a hardcover book, “Torrents of Rain, Miles of Misery: Flood of ’64” produced by the Daily Inter Lake and the Hungry Horse News. The 128-page book costs $39.95 and is available at the Inter Lake office, 727 E. Idaho St. in Kalispell, or by calling 755-7000.

Reporter Jim Mann may be reached at 758-4407 or by email at jmann@dailyinterlake.com.