The highest floodwater in 15 years is expected on the St. Joe River at St. Maries later this week as a fast-melting snowpack combines with heavy rain that’s forecast for Thursday and Friday.
Floods are also possible on other area rivers and Lake Coeur d’Alene.
The St. Joe could reach 38.8 feet by Friday at St. Maries, a level that will inundate low-lying farmland, cover portions of St. Joe River Road and approach flood gates in the levee at Aqua Park. The river was at minor flood stage at 33.1 feet on Monday.
National Weather Service forecasters said a tropical moisture plume in the middle of the Pacific Ocean on Monday is headed toward the Inland Northwest.
“It’s a very wet forecast,” said forecaster Rocco Pelatti.
Rainfall could begin today with the advance of thunderstorms from the south, possibly carrying large hail. That will be followed by the storm on Wednesday night and Thursday, which could dump 0.80 inches in Spokane and Coeur d’Alene.
Monday’s high of 81 at Spokane International Airport was several degrees off the record of 87 for the day.
Waterways already swollen by record March rain and snowmelt will only rise higher, Pelatti said.
Rivers that are being watched are the Moyie, the North Fork of the Coeur d’Alene, the Little Spokane at Dartford, the Kettle and the Grand Ronde.
The Yakima, Naches and Stehekin rivers in Washington are approaching or are above flood stage. Also being watched is the Yaak River in northwest Montana.
Lake Coeur d’Alene is expected to crest at just under 2,135 feet elevation on Sunday, which could cause flooding of homes, docks and roads. That will be the highest lake water since 2008, said Katherine Rowden, hydrologist with the weather service in Spokane.
This weekend the water will work its way down the Spokane River, where a moderate flood of 28 feet is expected. That equals a flow of 38,300 cubic feet of water per second.
On Monday, the Spokane was at 24,200 cfs and 25.4 feet on the city’s river gauge. Warm weather and high water have been drawing spectators to the Spokane Falls.
If the expected flow occurs, it would be the seventh-highest on record and the largest since May 2008.
Floodwaters are likely in Peaceful Valley, at Harbor Island, at the Riverpoint industrial area, along Upriver Drive and on the Centennial Trail.
The Coeur d’Alene River at Cataldo was at minor flood stage Monday and was expected to rise and fall before cresting at moderate flood stage on Friday at 46.1 feet.
Water could approach the Interstate 90 exit near Cataldo as well as cover Coeur d’Alene River and Latour Creek roads, the weather service said.
Temperatures will drop back to the upper 50s by Thursday with lows in the upper 30s and remain there through the weekend. Drier conditions are likely on Saturday and Sunday. Snow levels will drop in the mountains and slow the melt-off.