GENERAL OUTLOOK
Water year 2001 has started out in a dry mode. Seasonal precipitation for October - December was mostly in the 50-70 percent range, with basin snow packs East of the Cascades showing similar percentages. One important consideration this year is the relatively dry soils going into the snow accumulation season. This will result in more rain and snow melt runoff being lost in soils, reducing downstream runoff. Consequently, low runoff volumes are anticipated for most of the Columbia-Snake drainage.
The month of December was generally much drier than normal while temperatures were typically below normal.
Precipitation for December was low in the 40-60 percent range for most of the basin. The exceptions were the Okanagan River at 75 percent and the Upper Snake at 93 percent. Seasonal precipitation for the Columbia River above The Dalles is near 65 percent.
Early in the month, little precipitation was reported because of a ridge of high pressure that dominated through much of the period. Most of the precipitation that fell during December occurred during the middle of the month as high pressure broke down and a series of storm systems rolled in from the Pacific Ocean. A majority of the storm systems that impacted the region late in the month were weak and brought only light precipitation.
Pacific Northwest mean temperatures departed -1.3 degrees from normal relative to 1961 - 1990 normals (31 stations). Mean temperature departures ranged from -5.2 to 1.1 degrees.
Nor record high or low temperatures were reported during the month of December.
No daily precipitation records were tied or broken during the month of December.
For December, precipitation is:
53 percent of normal (1961 - 1990) at Columbia above Coulee,
52 percent of normal at the Snake River above Ice Harbor,
and 54 percent at Columbia above The Dalles.
For the water supply season, (October through December ) precipitation is:
60 percent of normal (1961 - 1990) at Columbia above Coulee,
84 percent of normal at the Snake River above Ice Harbor,
and 66 percent at Columbia above The Dalles.
January 1st snow pack is below average for the entire basin. Importantly, the lowest basin snow at this time is in the Upper Columbia - Kootenai in Canada and in the Pend Oreilla basin. Since these two areas contribute slightly more than half the runoff at The Dalles, they are important indicators of this years volume. It is important to note that several months remain of the snow accumulation season and improvements can still occur.
With deficient precipitation and drier than average soil moistures, December runoff was well below average. Most areas had December runoff in the 50 to 70 percent range. The January - July forecast runoff for the Columbia River at The Dalles is 80.4 million acre feet or 76 percent of average. This compares to a runoff of 98.0 million acre-feet last year.