By Scott Pattee

Water Supply Specialist

USDA-NRCS Snow Survey Office

What happened to our miracle March and La Nina, you may ask? Well, the warm dry trend from January and February continued through March. There were only three or four significant periods where average temperatures were cold enough for snow accumulation.

Otherwise, most days remained above freezing which caused the snowpack to mature and, in most cases, peak 1-3 weeks early.

April started out wet with substantial mountain snow, however, initial indications are that the moisture content was not significant enough to add much to the overall snowpack except at the highest elevations.

Snowmelt is well under way in most east side and lower elevation west side basins. The most recent forecast through next week indicates below normal temperatures with above normal precipitation.

Climate Prediction Center 3-month (Apr-May-Jun) forecast continues the previous track of below normal temperatures with equal chances of seasonal precipitation which is indicative of the forecasted Enso La Nina. The US Drought Monitor indicates the continuation of D0-D3 drought designation carried over from last year in eastern Washington.

Snowpack

The April 1 statewide SNOTEL readings were 80% of normal. The lowest readings in the state were at 5% of the 30-year median for April 1 in the Status Creek Basin. The Puyallup River Basin had the most snow with 126%. Westside medians from SNOTEL included the North Puget Sound River basin with 95% of normal, the Central and South Puget River basins with 87% and 82% respectively, and the Lower Columbia basins with 83% of normal. Snowpack along the east slopes of the Cascade Mountains included the Yakima area with 64% and the Wenatchee area with 80%. Snowpack in the Spokane River Basin was at 83% and the Upper Columbia River basins had 78% of the long-term median.

Precipitation

April precipitation accumulation was below normal in all but the Central and South Puget Sound basins. Statewide water-year average was 106% of average as of April 1. Monthly precipitation ranged from a high of 96% of normal in the Tolt and Skykomish basins to a low of 20% in the Entiat Basin. Some individual site reporting’s for the month include Pope Ridge 20% of normal, Dungeness 22%, Lost Horse 21%, Yakima Airport 19%, Winthrop 26% and Forks 70%. SNOTEL collects all forms 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. April 1 Reservoir storage in the Yakima Basin was 126% of average for the Upper Reaches and 127% of average for Rimrock and Bumping Lakes. The power generation reservoirs included the following: Coeur d’Alene Lake, 203,100-acre feet, 132% of normal and 85% of capacity; and Ross Lake within the Skagit River Basin at 102% of normal and 64% of capacity. Recent climate impacts and management procedures may affect these numbers on a daily or weekly basis.

Streamflow

Early winter forecasts for April-September stream flows are never quite as robust as they are later in the season when we know more about the winter climatology. At times only a few degrees warmer or cooler than forecasted can make or break stream flow predictions.

Volumetric forecasts are developed using current, historic and median snowpack, precipitation and streamflow data collected and coordinated by organizations cooperating with NRCS. Caution should be used when using early season forecasts for critical water resource management decisions since governing conditions are likely to change for the better or the worse.