The Jefferson River is expected to crest more than a foot above flood stage near Three Forks Thursday, causing “major” flooding in the area, the National Weather Service said Monday. Flooding also is expected in places along the Gallatin River between Gallatin Gateway and Logan this week.
The forecast calls for the Jefferson River to reach 9.4 feet by 6 p.m. Thursday. Flood stage is 8 feet and “major flood stage” is 9 feet, according to the Weather Service. The record flood stage, reached in 1997, was 9.9 feet.
The forecast for the Jefferson was substantially revised from Sunday’s predictions, which called for the river to crest at 10.5 feet. Weather Service hydrologist Gina Loss said forecasts are frequently revised based on rainfall and snow melt patterns.
At 8.5 feet, the river will begin washing over some county roads and bridges in the area, and may affect “several homes,” according to the National Weather Service.
At Logan, the Gallatin River is expected to crest more than two feet above flood stage late Wednesday or early Thursday, causing moderate flooding. Major flood stage at Logan is 11 feet, and the river is expected to crest at 10 feet, 3 inches.
Storms this week are expected to add some water to area rivers and reservoirs, and southwest Montana could receive up to 2 inches of rain over the next few days, she said. But cooler temperatures are expected to slow snow melt at the same time.
Nevertheless, nearly all of southwest Montana remained under a flood watch Monday, Loss said.
Snowpack is slowly melting and rivers and streams are “just now coming up,” she said. “Response has been slower than we expected.”
Loss said most of Montana remains flood prone, though.
“We still have a lot of water and we definitely aren’t done with our spring flood event yet,” she said. “We do have virtually the entire state under some type of flood watch or warning at this point in time. A lot (is) going on with the water.”
Also, she said, a “long stream of really warm days” is forecast to start later this week, and with snow water content at 200 percent of average in nearly every river basin in Montana, the threat of flooding will continue over the next several weeks.
“We haven’t lost as much snow as we should have for this time of year,” she said. “Some mountains are starting to lose some snow, but we have a long way to go.”
The SNO-TEL site at Darkhorse Lake near Wisdom, for example, is showing some 47 inches of snow water, where 25 inches is normal for this time of year, Loss said.
The Jefferson at Three Forks, which should start its climb toward flood stage Tuesday, is “one of the sites we’re watching fairly closely,” Loss said.
Three Forks Mayor Gene Townsend said in May that the city has pinpointed several sites where flooding from the Jefferson could enter town, and is prepared to sandbag as necessary.
“We will react if we have to,” he said.
View our Spring Flooding Gallery frequently, as new photos are added throughout the runoff season.