Ag Weather Forum

Snow Brings Slight Western Drought Easing

Bryce Anderson
By  Bryce Anderson , DTN Senior Ag Meteorologist
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The current snow water equivalent percent of median map shows many areas with significantly above normal snowpack for this point in the season. (NRCS graphic by Nick Scalise)

Following are highlights from the Drought Monitor summaries for the Far West and Northwest -- where much attention is being paid to the chance for drought easing this winter. -- Bryce

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FAR WEST -- The northern coast of California and the Sierra Nevada received half an inch to an inch of precipitation this week from Pacific systems. While the precipitation was beneficial to surface soil moisture, it had no effect on the long-term hydrological situation. In some areas, river base flows have not increased and groundwater and reservoir levels have not rebounded. Additionally, a well recently went dry in Cazadero (Sonoma County) in one of the typically more wet environments of northern California (coastal redwood forest). According to media reports, as of November 12, of 125 recreational lakes in California, 33 lakes held less than 25 percent of capacity, 19 of the 33 lakes held less than 10 percent of capacity and four lakes were empty. As noted by the U.S. Department of Agriculture, California statewide reservoir statistics (from the California Department of Water Resources/CDEC), updated through the end of October, show that this year's preliminary reservoir withdrawal stands at 6.92 million acre-feet (from a peak of 18.08 maf on March 31 to a probable minimum of 11.16 maf on October 31). This is just 84% of the historical average. Conservation is working, but storage is still precariously low, at second-lowest on record for this time of year, ahead of only 7.53 maf on October 31, 1977.

NORTHWEST -- Most days this week saw a continuation of the barrage of Pacific moisture and storm systems into Washington and northern Oregon. The frontal rains and upslope enhancement wrung out 6-plus inches of precipitation over a widespread area west of the Cascades. Precipitation totals for November 11-17 from observation stations in Washington included 20.79 inches at Quinault, 14.31 inches at Elma, and 13.03 inches at Olympia. Several other stations in western Washington reported over 8 inches of precipitation. Normals here this time of year can range up to 3 to 5 inches a week, so the precipitation that fell was 2 to 4 times the weekly normal. The rainfall raised streamflows and increased soil moisture, with some high elevation stations recording an increase of snowpack, up to 1 to 2 feet of new snow at some stations.

In Oregon, long-term precipitation deficits remained even with these last few storms, streamflows have been slow to respond, and reservoirs were near empty (the Willamette is well into conservation storage). It will take many more storms, with the accumulation of a thick winter mountain snowpack, to refill the reservoirs during the spring melt season.

With a westerly circulation, the air masses dried out as they crested the Cascades, so central and eastern portions of Washington and Oregon received only a few tenths of an inch of precipitation at best. Parts of the Rockies in northern Idaho and northwest Montana received half an inch or more of precipitation, which helped increase the snowpack at some high-elevation stations, but snow depth reports were only a few inches to a foot at most stations. Precipitation amounts declined to the east and south, with parts of northern Wyoming and southeast Montana receiving less than a tenth of an inch or no moisture.

(CZ/AG)

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