GENERAL OUTLOOK
Late Summer and early Fall conditions were generally warm and drier than average. In November weather patterns changed to a cooler and wetter regime. October - November precipitation ranges from 70 percent in parts of southern Idaho and southeast Oregon to 150 percent in the Okanogan. The October-November precipitation for the Columbia River above The Dalles is 111 percent.
The January 1st snow accumulations mirror the precipitation pattern, with snow water equivalents ranging from 80 percent in southern Idaho and southeast Oregon to as high as 180 percent in parts of the Washington Cascades.
Fall runoff has been below average in the Upper Columbia, Pend Oreille and Clearwater Rivers, while the rest of the area has experienced near average to above average runoff through the Fall.
The January-July forecast for the Columbia River above The Dalles is 116.0 million acre feet or 110 percent of the 30 year average. This compares to a January-July runoff of 104.1 million acre feet last water year.
Despite a major arctic air outbreak across the region after mid month December trended toward above normal temperatures with frequent precipitation occasionally heavy particularly within the second and last week of December.
Mean temperatures departed +0.67 degrees (31 stations) from normal for the pacific northwest relative to 1961-1990 normals. Mean temperature departures ranged from -5.2 to 7.5 degrees.
A reported daily record high temperature occurred at Helena on the 17th (58 degrees) and a record minimum temperature climbing to 46 degrees at Portland was observed on the 12th and again on the 28th. The only trace of frigid arctic air beyond mid December was reflected in a record low temperature at Missoula (-20 degrees on the 20th).
Astoria saw record daily rainfall on the 1st (2.43 inches).and on the 27th (2.23 inches), Eugene on the 27th (2.25 inches), Seattle on the 27th (1.53 inches) and Olympia on the 7th (1.13 inches).
Frequent pacific frontal disturbances dominated most of our western tier basins up through mid December and again in the last week of the month. Disturbances produced pronounced periods of warm locally heavy rains with snowmelt and sharp rises in streamflows focused mostly in western Washington and western Oregon basins just prior to mid month and again near the last week in December. A pacific disturbance scouring out arctic air around the Christmas holidays resulted in local freezing rain problems mostly confined to Oregon and Washington. Regarding snowpack conditions several snowmelt and build events resulted in little overall snow pack changes.
For December precipitation was 120 percent of normal (1961-1990) at Columbia above Coulee, 100 percent of normal at the Snake river above Ice Harbor and 117 percent at Columbia above The Dalles.
