GENERAL OUTLOOK
Volumes decreased in almost all basin areas. Generally, snow accumulations were less than average for the month and March precipitation was also below average basin wide. The area that is an exception is the Willamette River area and southwest Oregon, where snow accumulated at greater than average rates, but volume still decreased due to less than average precipitation.
Precipitation during March ranged from less than 50 percent in most of eastern Oregon and in the Flathead River area in Montana to 90 percent in the Upper Columbia in Canada and in the Kootenai River basin. The October -March seasonal precipitation for the Columbia River above The Dalles is 116 percent.
Basin snow water equivalents are still well above average for most of the Columbia - Snake basin but down from the March 1st percents by 3 - 20 percent. Greatest departures from average (above 200 percent) occur in the Cascades in southwest Washington and in Oregon.
Snow water equivalents are greatest in the northern basins (120 - 160 percent) and least in southern areas of Idaho at 80 - 105 percent. Runoff for the month was generally above average caused by a 5 - 7 day warm spell during the month which produced some moderate snowmelt peaks. The average adjusted runoff at The Dalles for the month of March was 126 percent.
Volumes decreased 5 - 20 percent in most areas from March 1st forecasts. Volume runoffs now range from greater than 130 percent in the Cascades in Washington and Oregon, on the Spokane River area and on the Weiser River in central Idaho to less than 100 percent in parts of southern Idaho and southeast Oregon. The January - July forecast from the Columbia River above The Dalles is 128.0 million acre feet or 121 percent of average. This compares with a volume runoff of 104.1 million acre feet in 1998.
Mid-late March warming and snowmelt focused along the middle-upper Snake was countered by a dominant winter-like storm pattern, elsewhere interrupted only a few times by transient widespread fair weather episodes across the region. Mean temperatures departed +0.5 degrees from normal for the Pacific Northwest relative to 1961-1990 normals (31 stations). Mean temperature departures ranged from -3.2 to 4.5 degrees.
Astoria saw record daily rainfall on the 12th (2.01 inches) and Great Falls on the 31st (0.44 inches - that also included a record 24 hour snowfall total of 8.1 inches for the 31st). Daily record temperature records were broken at Astoria (69 deg on the 19th) Pocatello (72 deg on the 20th and 25th) and Kalispell (64 degrees on the 19th 68 on the 21st and 61 on the 25th).
Mostly frequent Pacific winter-like frontal disturbances with plenty of lingering unsettled post frontal conditions produced more valley rain and surprisingly low mountain snows focused largely into western Washington and northwestern Oregon. This was contrasted by below normal precipitation and above normal warming that started near the middle of March across eastern Oregon, south-central Idaho and into southwestern Montana. Resulting interior snowmelt runoff was particularly pronounced in western Idaho's Weiser river basins despite this snowmelt episode exhausting a healthy portion of low elevation snow in southeastern Oregon's Owyhee. Snowpacks across the region are still considered to be significantly above normal.
For March, precipitation was 137 percent of normal (1961- 1990) at Columbia above Coulee; 185 percent of normal at the Snake river above Ice Harbor; and 156 percent at Columbia above The Dalles.