GENERAL WEATHER SUMMARY
February 1, 2000
Water supplies have improved for all Snake River tributaries, while in the northern portions of the basin water supply forecasts are little changed from last month. Increased volumes also occurred in most Oregon basins.
Precipitation during January was above average for most of the Oregon and Idaho basins, and near average for the northern basins. The wettest area was in southwest Oregon where frequent storms pushed precipitation to nearly twice the average. Seasonal precipitation for the Columbia basin above The Dalles is at 104 percent.
Snow conditions for basins in most of Washington, northern Idaho, British Columbia and western Montana have remained near to slightly below average, unchanged from last month. However, snow conditions in southern basins have increased dramatically with increases of 20 - 50 percent from January 1st. The greatest increases were in western Oregon and in the Great Basin in Oregon. Runoff for January was above average in the Upper Columbia and Kootenai and near to below average for the rest of the basin.
The February 1st forecast for the January - July period at the Columbia River above The Dalles is 106 million acre feet or 100 percent of average, an increase of 1 percent from last month. This compares to a runoff of 124.1 million acre feet for last year.
A strong jet stream located along the southern periphery of a trough of low pressure across the Gulf of Alaska guided storm systems into the Pacific Northwest on a frequent basis. When systems were able to tap moisture from the subtropics, heavy precipitation was often the result, especially across the Olympic Peninsula, Cascades, and coastal range. Breaks in this overall weather pattern occurred for only a couple of days early in the month and again for a slightly longer period at the end of the month. During these hydrologically benign weather periods, high pressure maintained dry weather and high freezing levels.
Pacific Northwest mean temperatures departed +3.0 degrees from normal relative to 1961 - 1990 normals (31 stations). Mean temperature departures ranged from -0.9 to 11.7 degrees.
No temperature or precipitation records occurred in the month of January. For January, precipitation was 100 percent of normal (1961 - 1990) at the Columbia above Coulee; 119 percent of normal at the Snake River above Ice Harbor; and 103 percent at the Columbia above The Dalles.