Mountains in the Inland Northwest have enough snow to keep most of the region’s rivers flowing at 80 to 90 percent of normal, according to a water supply outlook issued this week.
Some rivers may see flows well below normal, including those in north central Washington and the Okanogan Valley, said Royce Fontenot, hydrologist with the National Weather Service in Spokane.
While snow inundated the lowlands this winter, mountain areas that provide water for spring and summer stream flows have below-normal snow packs, largely because of dry weather in late autumn and again in late January and most of February.
“We basically had winter in three weeks,” Fontenot said about the region’s winter storms that started on Dec. 17.
February was particularly dry with most of the region getting only 55 to 60 percent of normal rain and snow.
The stream-flow forecast was prepared by various government agencies through the Northwest River Forecast Center.
The latest outlook shows that the Spokane River system, including the Coeur d’Alene and St. Joe rivers, should flow at 80 percent of normal this spring and summer.
Stream flows are predicted to be 87 percent of normal on the Columbia River at Grand Coulee Dam; 84 percent on the Kootenai River at Bonners Ferry; 86 percent on the Pend Oreille River at Box Canyon Dam; 82 percent on Priest River; and 87 percent on the Clearwater River at Spalding.
The Snake River is forecast to flow at 75 percent of normal at Lower Granite Dam. Also, the Okanogan, Similkameen and Methow rivers may see only 60 percent of their normal flow.
Fontenot said the lower flows in central Washington could cause problems for farmers that rely on irrigation supplies from those systems. He said stream basins on the east side of the Cascades don’t have as much snow pack, and that the relative shortage of precipitation there could lead to an early-stage drought.
Dry conditions have also prevailed along the upper Columbia Basin growing areas, including Lincoln, Grant, Adams and Douglas counties, an area that is now considered “abnormally dry,” he said.
A forecast of below-normal stream flows doesn’t eliminate the risk of spring flooding. Warm weather and rain could trigger a rush of water even with the leaner snow pack, Fontenot said.
“If we get rain on top of snow, we can still get a flood,” he said.