Ag Weather Forum

The USDA weekly weather and crop bulletin for December 23 has a very thorough review of the extent of drought issues in California. They are worth noting for the combination of out-of-bounds dryness and out-of-bounds heat that have plagued the Far West. Details are below.

Bryce

Twitter @BAndersonDTN

During the last 3 weeks, precipitation in California has begun to chip away at staggering, 3-year rainfall deficits. The rain has boosted topsoil moisture, benefited winter grains, and allowed rangeland and pastures to begin a gradual recovery process.

However, major long-term impacts—such as low reservoir levels and groundwater depletion—remain. In addition, California's recent spate of wet weather did not result in much high-elevation snow, leading to concerns about a spring runoff shortfall unless "colder" storms materialize during the next few months.

California recently completed its driest 36 months on record for all 3-year periods ending in November, according to the National Climatic Data Center. From December 2011-November 2014, California's precipitation averaged 45.39 inches, just 67 percent of normal. Effectively, the state has received 2 years of precipitation in the last 3 years. Previously, the previous driest such period occurred from December 1974-November 1977, when an average of 47.68 inches fell.

Consistently high temperatures have complicated California's drought situation by increasing evaporation rates and boosting irrigation demands. Since 1895, California's temperatures have never been higher than they have been over the last 3 years. From December 2011-November 2014, California's average temperature of 60.0 degrees Fahrenheit was 2.6 degrees Fahrenheit above the 20th century mean.

California's 154 in-state reservoirs continue to languish at near-record low levels. At the end of November, storage was just 55 percent of the long-term average, according to the California Department of Water Resources. Only 1977 featured lower storage at this time of year. During the current drought, which began in late 2011, statewide reservoir storage fell below this historic average in March 2013. This lag in reservoir impacts helps to highlight the disconnect that exists in California (and elsewhere in the western U.S.) between meteorological drought and managed water systems.

In the Sierra Nevada, snowpack has improved during a stormy period in December 2014 but remains below average. The snowpack on December 22, 2014 measured five inches. In the 2012-13 season, that snowpack amount measured eight inches--with the normal amount for the date at 10 inches.

For the three weeks from December 1-21, 2014, these are the rainfall totals and normal values (in inches) for selected California cities:

Location Total Normal

San Francisco Airport 10.62 2.59

Redding 10.24 4.11

Eureka 8.84 5.58

Sacramento 8.59 2.11

San Diego 4.42 0.95

Los Angeles Airport 3.73 1.24

Fresno 2.29 1.08

Bakersfield 1.87 0.64

(ES)

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