Series of weather events set up extreme flooding | State and Region


Meteorologists said on Monday that a series of significant weather events during an unusual spring season created “never…before-seen” water levels in high mountain areas that resulted in destructive flooding around from Montana.

As authorities evacuated residents of Red Lodge and Yellowstone National Park closed its entrances due to extreme flooding, National Weather Service forecasters said major towns downstream are expected to experience peak flows from Monday evening.

In neighboring southwest Montana, Jim Brusda, chief meteorologist for the National Weather Service in Great Falls, says three contributing factors are causing rivers to rise rapidly.

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First, April and May, unusually cool for the season, kept snow accumulation in the mountains, and late spring snowstorms significantly worsened the snow accumulation.

Second, the temperature of the existing snowpack, measured by satellite, was 32 degrees due to the angle of the sun at this end of the year.

Third, Montana experienced several days of heavy precipitation at higher elevations.

The three factors combined, Brusda said, caused the snowpack to “fade away quickly instead of melting more gradually.”

“This is bringing the Gallatin River above (minor) flood stage as we speak near the town of Logan,” Brusda said Monday afternoon. “But we don’t expect major flooding on the Gallatin.”

Brusda forecast the Gallatin River flooding to last a few days, with conditions beginning to improve on Thursday.






Water rushes over House Rock as the Gallatin River reaches flood stage on Monday.


Photo courtesy of the Gallatin County Sheriff‘s Office


Dan Borsum, senior forecaster at the Billings National Weather Service office, similarly described “really big” events that triggered flooding in south-central Montana watersheds: a snowstorm during the Memorial Day which has deposited moisture in the mountains and the recent series of rain events. which dropped 2 to 3 inches in some areas.

Much of the heavy rain and snow fell on the south side of the Absaroka-Beartooth region, Borsum said, but that moisture is flowing north and into watersheds like Paradise Valley and Clarks Fork from the Yellowstone River. Soda Butte Creek near Cooke City and Silvergate reported water levels of 4 feet above bridges there, Borsum said.

“You don’t normally think of floods that high in the mountains,” Borsum said. “…The levels that have been observed at these upstream locations have never been observed before.”

Forecasts

Water levels peaked Monday afternoon in upper river regions in that part of the state, Borsum said. The next question is what’s going on with the towns downriver, including Livingston, Laurel, Columbus and Billings. According to Borsum, river levels are expected to peak in:

  • Livingston by Monday evening;
  • Columbus between 4 a.m. and 7 a.m. Tuesday;
  • Laurel around noon on Tuesday; and
  • Billing between 2 p.m. and 6 p.m. on Tuesday.

“Laurel and Billings, in particular, could see their high waters continue for longer periods,” Borsum said. “We’re still trying to get a sense of that.”

Looking ahead, temperatures in south-central Montana are expected to reach the 90 to 100 degree range in the coming days, with temperatures in the mountains hovering in the 70s, Borsum said. Monday’s temperatures had cooled enough to adequately slow snowmelt, he said, but when those highs arrive later this week, the melt will pick up speed again.

“It shouldn’t be as high as it has been,” Borsum said. “But with all the effort to fix the infrastructure, people should know that a ton of water is still about to go down in the area.”

Excess water in the Gallatin and the emergency release of water from the Hebgen Dam into the Madison River put the Missouri River near Toston under flood watch.

Hebgen Dam operators are releasing more water than usual as they attempt to limit pressure on the dam as crews work to repair parts of the dam that failed in November 2021. This water is heading towards Ennis, which is also in flood watch, before it reaches the Missouri River.

“The Toston area should only experience minor flooding for about a day or two,” Brusda said. “Flooding is expected to be confined to the edges of the Missouri River in this area.”

No flooding is expected further downstream as the Canyon Ferry Reservoir collects all runoff.

The Great Falls National Weather Service is monitoring the glacier region and the Rocky Mountain Front as up to 2 inches of rain are forecast to fall below 50.00 feet and 3 to 4 inches of snow above 6,000 feet at the over the next two days.

As long as high elevation precipitation falls as snow, as expected, flooding is expected to remain minor along the eastern front of the Northern Rockies. But if the precipitation falls in the form of rain, it could mean more severe flooding in this region.

Brusda urged people not to recreate on the rivers at this time as the rivers are “washing away” leftover debris from last year’s low waters.

“Anyone recreating on the river right now should know this is not a good situation,” Brusda said. “There is a lot of debris in the river and it is flowing too high and very fast.”

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