GENERAL OUTLOOK
Continued dry conditions have, again, lowered seasonal volume expectations. Dry soils will decrease streamflows as spring melt and rainfall satisfy soil moisture deficits. Several forecast sites in the basin will have record low runoff.
Like January, February storm systems split as they approached the Pacific Northwest. Most of the energy associated with these systems dove south to form fairly strong low pressure systems off the coast of California. Pacific Northwest precipitation totals were below normal.
Pacific Northwest mean temperatures departed -3.4 degrees from normal relative to 1961-1990 normals (31 stations). Mean temperature departures ranged from -10.0 to 2.3 degrees.
NO TEMPERATURE OR PRECIPITATION RECORDS WERE BROKEN IN FEBRUARY.
Some items of note, Astoria experienced their third driest February since 1953, Portland their 5th driest February since 1931, Medford their 19th driest February on record, Salem their 6th driest February since 1892.
For FEBRUARY, PRECIPITATION is:
55 percent of normal (1961-1990) at COLUMBIA ABOVE COULEE,
55 percent of normal at THE SNAKE RIVER ABOVE ICE HARBOR,
and 51 percent at COLUMBIA ABOVE THE DALLES.
For the WATER SUPPLY SEASON (October through February), PRECIPITATION is:
56 percent of normal (1961-1990) at COLUMBIA ABOVE COULEE,
72 percent of normal at THE SNAKE RIVER ABOVE ICE HARBOR,
and 58 percent at COLUMBIA ABOVE THE DALLES.
Dry conditions limited February snow accumulations. March 1st snow water equivalents range from 70 percent in Southern Idaho and Southeast Oregon to less than 50 percent on the Kootenai river and on the Boise, Payette and Weiser rivers in Idaho. Snow water equivalent percentages were unchanged or down slightly from February 1st values. Snowpack deficiences are greatest in British Columbia, where several snow reporting sites have the lowest snow water equivalents of record for March 1st.
Observed runoff for February continued to be very low. The Upper Columbia in Canada and the Upper Snake had February runoff in the 70-90 percent range. Most other drainages had runoff of 40-60 percent. The lowest runoff at 15-30 percent of average was observed on the Yakima basin in Washington and the Spokane river tributaries in Idaho. The February runoff for The Columbia river at The Dalles was less than 50 percent.
Deficient precipitation and snow accumulations during February dropped forecasts another 4-10 percent on the Columbia river and 5-20 percent on the Snake river. The January-July forecast for the Columbia river at The Dalles is 58.6 million acre feet (MAF) and 55 percent. This compares to a runoff of 98.0 MAF last year.