Washington Water Supply Outlook for March

Cold and dry conditions gripped most of the state last month. With only a hand full of exceptions, monthly precipitation was much below to just near normal. It may seem like it has been wet and snowy and in truth it has been in both the mountains and lowlands. It just hasn’t been enough to keep up with what we should be seeing this time of year, causing greater divergence below normal as we go through time.

The most recent forecast through late-March shows a probability for below normal temperatures and equal to slightly above normal precipitation. NWS 3-month (Mar-Apr-May) forecast indicates slightly below normal temperatures and equal chances of above, below, or normal precipitation which is indicative of the Enso La Nina pattern that we have experienced for the 3rd year in a row. The US Drought Monitor shows an expansion of abnormally dry conditions into the south-west part of the state.

Snowpack: The March 1 statewide SNOTEL readings were 97% of normal, a slight increase since February 1. The lowest readings in the state were at 72% of the 30-year median for March 1 in the Status Creek Basin. Omak and Sanpoil creeks recorded the highest percentage of snow with 146% and 142% respectively. Westside medians from

SNOTEL included the North Puget Sound River basins with 87% of normal, the Central and South Puget River basins with 102% and 96% respectively, and the Lower Columbia basins with 105% of normal. Snowpack along the east slopes of the Cascade Mountains included the Yakima area with 87% and the Wenatchee area with 88%.

Snowpack in the Spokane River Basin was at 94% and the Upper Columbia River basins had 113% of the longterm median.

Precipitation: Precipitation accumulation was below normal across most of the state. Statewide Water-year average increased slightly to 85% of normal as of March 1. Not surprisingly the Central Puget Sound convergence zone saw the highest monthly precipitation at 108% of normal, mostly in the form of snow. Stevens Pass gained 9.9 inches of precipitation, of which 9.2 inches recorded as snow water equivalent. SNOTEL collects all form of precipitation including, rain, snow, sleet, and hail.

Reservoir: Seasonal reservoir levels in Washington can vary greatly due to specific watershed management practices required in preparation for irrigation season, fisheries management, power generation, municipal demands and flood control. March 1 Reservoir storage in the Yakima Basin was 386,300-acre feet, 79% of median for the Upper Reaches and 88% of median for Rimrock and Bumping Lakes. The power generation reservoirs included the following: Coeur d’Alene Lake, 47,000-acre feet, 47% of median and 20% of capacity; and Ross Lake within the Skagit River Basin at 96% of average and 54% of capacity. Recent climate impacts and management procedures may affect these numbers on a daily or weekly basis.

For more information contact your local Natural Resources Conservation Service office.