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Higher Temperatures and Rain Melt Snowpack, Spring Flooding Possible

Monday, March 7, 2016   (0 Comments)
Posted by: Breanne Chavez
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Higher Temperatures and Rain Melt Snowpack, Spring Flooding Possible

SPOKANE, WA (March 7, 2016) –El Nino did a number on Washington State this past month with temperatures ranging from 5-15 degrees warmer than normal. However rain was plentiful in most areas of the state. According to the USDA Natural Resources Conservation Service, this combination not only melted low and mid elevation snow but also led to a decline in snowpack percentages.

“The decline in snowpack was due to the lack of normal snow accumulation for February and not the melt. These conditions also attributed to the sharp increase in snowpack density, or quantity of water in the snow, which means that we are about a month ahead of where we should be,” said NRCS Water Supply Specialist, Scott Pattee.

According to Pattee, if these trends continue we will see an early start to spring melt and the possibility of rare spring flooding. The latest NWS 3-month outlook short term forecasts are calling for cool and wet weather for the first half of March but then falling back into a warmer and possibly dryer second half. Long range forecasts for the spring continue to be warmer and dryer than normal with less certainty on precipitation amounts.

The March 1 statewide Snowpack Telemetry (SNOTEL) readings were 100% of normal, down from 109% on February 1 and 120% on January 1. The Skykomish River Basin reported the lowest readings at 62% of the 30-year median for March 1 and the Methow had the most snow with 135%. Most basins reported a net loss from last month primarily due to the lack of fresh snow.  Westside medians from SNOTEL, and March 1 snow surveys, included the North Puget Sound river basins with 93% of normal, the Central and South Puget river basins with 84% and 82% respectively, and the Lower Columbia basins with 101% of normal.  Snowpack along the east slopes of the Cascade Mountains included the Yakima area with 98% and the Wenatchee area with 108%.  Snowpack in the Spokane River Basin was at 83% and the Walla Walla River Basin had 107% of the long term median.

The state received above normal precipitation for the month of February keeping year-to-date statewide SNOTEL averages above normal at 130%. Only north central and south east parts of the state fell below 100%.  Quillayute State Airport measured 152% of normal rainfall. The wettest SNOTEL in the state was Skookum Creek, located in the Tolt River Basin, which collected 23.5 inches of precipitation or 201% of normal during the month of February.

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. A very wet February helped buffer some reservoir levels, supplementing any chance of lower snow levels. March 1 Reservoir storage in the Yakima Basin was 580,000-acre feet, 129% of average for the Upper Reaches and 199,000-acre feet or 145% of average for Rimrock and Bumping Lakes. The power generation reservoirs included the following: Coeur d’Alene Lake, 171,000 acre feet, 129% of average and 72% of capacity; and the Skagit River reservoirs at 43% of average and 73% of capacity.  Recent climate impacts and management procedures may affect these numbers on a daily or weekly basis.

March 1 marks a time where we are about 80% through winter thus making streamflow forecasting a much more attainable target. At times only a few degrees warmer or cooler than forecasted can make or break stream flow predictions. April-September forecasts for some Western Washington streams include the Cedar River near Cedar Falls, 121%; White River, 117%; and Skagit River, 114%. Some Eastern Washington streams include the Yakima River near Parker 123%, Wenatchee River at Plain 109%; and Spokane River near Post Falls 92%. Volumetric forecasts are developed using current, historic and average snowpack, precipitation and streamflow data collected and coordinated by organizations cooperating with NRCS.

Since 1939, NRCS has conducted snow surveys and issued regular water supply forecasts. Since the late 1970s, NRCS has been installing, operating and maintaining an extensive, high-elevation automated system called SNOTEL, designed to collect snowpack and related climatic data in the western U.S. and Alaska.

View the latest Snow Survey and Water Supply Forecast information by state. Other resources on drought include the U.S. Drought Monitor.For information on USDA’s drought efforts, visit USDA Disaster and Drought Information. And to learn more about how NRCS is helping private landowners deal with drought, visit the NRCS website.

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