A wet January helped offset what had been an extremely dry water year since October, according to Ryan Lucas, hydrometeorologist for NOAA's Northwest River Forecast Center. But significant snowmelt over the past week is having the opposite impact on the region's water supply, he said.
"After these three dry months, we had a pretty good January across much of the Columbia Basin, especially in the northern Cascades," Lucas said during the center's Feb. 5 water supply webinar. But broad swaths of the basin in eastern Oregon and the Snake River are still projected to have below normal water supply, partly due to significant snowmelt and runoff from Jan. 30 through Feb. 2.
Some areas—especially in western Washington and a few locations in eastern Oregon—are also experiencing flooding. Runoff conditions continue to be generally high for this time of year, he said.
As of Feb. 5, the April-to-September water supply forecast for the lower Columbia River at The Dalles Dam is 105 percent of normal—1 percent higher than it was a month ago, he said.
The forecast for lower Snake River at Lower Granite Dam is 95 percent of normal—12 percent lower than it was in early January.
Forecasts of water supply for the upper Snake River areas went down, and are now at 97 to 114 percent of normal.
Middle Snake River tributaries are suffering the most, predicted to be between 82 and 98 percent of normal water supply.
But the upper Columbia River above Grand Coulee Dam is 112 percent of normal—8 percent higher than it was in early January.
Runoff from recent rains had a bigger impact in basins on the West Coast. The Willamette River at Salem is currently forecast to have 86 percent of its normal water supply—a loss of 9 percent from last month. Other westside rivers range from 89 to 104 percent of normal.
As for total precipitation so far this water year, Lucas said, "It's looking better than it did a month ago . . . We got a pretty good amount of snow in the month of January. It definitely brought those numbers up."
Forecasters expect the next three or four weeks to be colder and drier than normal, which is also playing a role in the water supply outlook, he said.