General Outlook

So much for the doom and gloom as reported last month. This Awesome April brought most of the winters missing snow in just one short month. Measured in feet not inches snowpack piled up in record fashion nudging out April 2011 for the king of come backs. Going back to 2009 there have only been 2 significant years where April saved the day. Typical April snowfall is light and often followed by warm weather that simply evaporates it to the atmosphere, not adding to the overall snowpack and subsequent runoff. Below normal temperatures slowed stream runoff to below and much below normal levels.

The most recent forecast through mid-month indicates below normal temperatures with near normal precipitation. Climate Prediction Center 3-month (May-Jun-Jul) forecast of near to below normal temperatures with below normal chances of seasonal precipitation. The US Drought Monitor indicates the continuation of D1-D3 drought designation carried over from last year in eastern Washington.

Snowpack

The May 1 statewide SNOTEL readings increased to 114% of normal. As the state begins to drift into the heart of melt season some basins will react differently to end of season snowfall. Westside medians from SNOTEL included the North Puget Sound River basin with 108% of normal, the Central and South Puget River basins with 32% and 111% respectively, and the Lower Columbia basins with 114% of normal. Snowpack along the east slopes of the Cascade Mountains included the Yakima area with 101% and the Wenatchee area with 118%.

Snowpack in the Spokane River Basin was at 114% and the Upper Columbia River basins had 107% of the long-term median.

Precipitation

May precipitation accumulation was near normal throughout the state. Statewide water-year average was 109% of average as of May 1. Monthly precipitation ranged from a high of 376% of normal in the Colockum Drainage to a low of 74% in the north-east corner of the state. Some individual site reporting’s for the month include Pope Ridge 207% of normal, Dungeness 292%, Lost Horse 230%, Hozomeen Camp 156%. 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. May 1 Reservoir storage in the Yakima Basin was 115% of average for the Upper Reaches and 102% of average for Rimrock and Bumping Lakes.

Coeur d’Alene Lake, 170,100-acre feet, 81% of normal and 71% of capacity; and Ross Lake within the Skagit River Basin at 94% of normal and 47% of capacity. Recent climate impacts and management procedures may affect these numbers on a daily or weekly basis.

Streamflow

Early winter forecasts for May-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.