Warm weather starting today is expected to trigger renewed runoff from the higher elevations of the Rockies, sending the Pend Oreille River above flood stage next week, forecasters said Thursday.
Because of flooding problems downstream from Newport, Washington, in recent years, the federal government announced Thursday that it is lowering the threshold flow for minor flooding on the Pend Oreille from 100,000 to 95,000 cubic feet per second. The mean flow in 2013 was 24,590 cfs.
Temperatures at higher elevations are forecasted to reach the 60s during the day and middle 40s at night at least through Thursday.
Spokane will see highs in the lower 80s and lows in the 50s under mostly sunny skies.
Already, rivers have been flowing at high levels in Western Montana from warm weather last week.
The Pend Oreille River at Albeni Falls Dam east of Newport should reach the 95,000 cfs flood stage on Tuesday and rise to nearly 100,000 cfs by Thursday. The forecast only extends until Thursday so it is possible the river could crest even higher.
The National Weather Service announced Thursday that the new flood flow threshold stemmed from the experiences during floods in recent years, including 2011.
Forecasters said that they learned in those previous floods that private property and public infrastructure were affected at levels below the old threshold of 100,000 cfs.
The new flood flow was established in conjunction with the U.S. Army Corps of Engineers and the Pend Oreille County Department of Emergency Management.
Under the adjusted levels, minor flooding starts at 95,000 cfs; moderate flooding remains at 110,000 cfs; and major flooding will go from 120,000 to 130,000 cfs.
The 21 floods on record above the new threshold on the Pend Oreille occurred between May 21 and June 25, with 18 of them in June.
Lake Pend Oreille, which feeds the Pend Oreille River, should remain about two feet below flood stage at an elevation of 2,062 feet.
Elsewhere, the Kootenai River is expected to rise again next week, but remain 4 feet below flood stage at Bonners Ferry. The river may have hit its peak for spring runoff for the year at 63 feet last weekend. The river is expected to crest again about Tuesday at 61 feet. Minor flood stage is 64 feet.
Also, the Okanogan River near Tonasket, Washington, should rise again to minor flood stage starting Monday and stay there through much of next week. The river crested last week above minor flood stage, but dropped with cooler weather this week.
The Spokane River appears to have peaked for the season. On May 9, the river ran at 20,000 cfs. On Thursday it was running at 17,600 cfs, about its mean flow for the month of May.