HELENA – Heavy thunderstorms are expected to compound flooding problems across Montana this week by adding sizable amounts of water to already high rivers and saturated soil, meteorologists said Monday.
A strong storm system heading east from California could bring up to 2 inches of rain across the state and 2-inch hail in eastern and central Montana, according to the National Weather Service. The rain and warm temperatures will speed the melting snowpack that was already projected to raise river levels later in the week.
Tom Frieders, a Weather Service meteorologist in Billings, said flash flooding and isolated tornadoes are possible from Billings to Roundup, which has already been hit hard by flooding.
Heavy rain of up to 8 inches and melting snow pack caused major flooding in parts of Montana last month. The inundated Missouri River also caused flooding problems in North and South Dakota.
Frieders said it’s hard to predict how high the water will get this time until forecasters see how much rain the thunderstorms bring and how much snowpack melts. But the Musselshell River, already near flood levels, is expected to flood again.
“It’s all coming together, both thunderstorms and significant runoff from melting,” Frieders said.
Elsewhere in Montana, the rains and melting snow are likely to have the same impact.
The Clark Fork River in western Montana could reach moderate flood stage by the middle of the week.
Meteorologists are predicting the river could rise to 12 feet, 2 feet above flood stage. The river, near Missoula, could flood residential areas, meteorologist Leeann Allegretto of Missoula said.
Allegretto said the Bitterroot and Flathead Rivers are also likely to reach low to moderate flood stage.
In northern Montana, the Milk River recently reached flood stage and is likely to rise higher.
Also Monday, U.S. Army Corps of Engineers announced they were going to release massive amounts of water from the Fort Peck dam Tuesday. The engineers were originally planning on releasing a record 50,000 cubic feet per second of water from the dam mid-June. The increased water flow into the Missouri River is already causing flooding in residential areas downstream.
More water is expected to cause flooding in low-lying areas downstream on the Fort Peck Indian Reservation and in the Dakotas.
Improvised earthen levees built around South Dakota cities, including the capital city of Pierre, are currently blocking the water from entering parts of the city.