Monday, December 22, 2014

U.S. Drought Monitor News

Special California Drought Update through Dec. 16 from USDA

Dec 18, 2014

By Brad Rippey, Meteorologist, Office of the Chief Economist, U.S. Department of Agriculture

PLEASE NOTE: This update is specific to California due to significant precipitation that has fallen since Thanksgiving.

Since Thanksgiving, several systems have brought significant precipitation across California. In valley locations, rain has boosted topsoil moisture, benefited winter grains, and helped to revive rangeland and pastures. According to the U.S. Department of Agriculture’s National Agricultural Statistics Service, 30 percent of California’s rangeland and pastures were rated in good to excellent condition on Dec. 14, compared to just 15 percent on Oct. 26. Also on Dec. 14, four-fifths (80 percent) of California’s winter wheat was rated in good to excellent condition.

During the three-week period from Thanksgiving Day (Nov. 27) to Dec. 17, rainfall totals at selected California locations included:

Location

Total in inches

Normal in inches

Percent of Normal

Mt. Shasta City

11.63

4.94

235

San Francisco

11.30

2.41

469

Redding

9.84

4.03

244

Sacramento

8.15

2.01

405

San Diego

4.42

0.92

480

Los Angeles

3.95

1.14

346

Fresno

2.30

0.98

235

Bakersfield

1.87

0.60

312

During California’s wet spell, most of the precipitation has been produced by “warm” storms. As a result, Sierra Nevada snow levels have been very high – sometimes above 7,000 feet. Consequently, high-elevation snowpack is neither deep nor well established. According to the California Department of Water Resources, the average water content of the high-elevation Sierra Nevada snowpack was less than 4 inches on Dec. 17 – only 48 percent of normal for this time of year. In a typical winter, nearly 30 inches of water builds up in the Sierra Nevada snowpack by April 1.

With most of the precipitation falling as rain, some of California’s major reservoirs received a boost from runoff. In general, the runoff led to capacity increases (at least 6 to 10 percentage points) in major reservoirs across northern and central California. For example, the respective percent of capacity values for Nov. 28 for Trinity, Shasta, Oroville, Folsom, and San Luis Lakes were 23, 23, 26, 28, and 23; on Dec. 16, they increased to 29, 32, 33, 38, and 33 percent. Respective historical averages on Dec. 16 for those five reservoirs are 44, 53, 54, 79, and 52 percent.

The latest U.S. Drought Monitor, issued Dec. 18, indicates that there was a substantial reduction in D4 (exceptional drought) coverage in northern and central California. Statewide, D4 coverage fell from 55 to 32 percent -- the smallest area in exceptional drought since early June 2014. However, overall drought (D1 to D4) coverage declined only slightly in California, from 99.7 to 98.4 percent. In other words, nearly all of the state remains in drought, although the drought intensity has decreased by one category in parts of northern and central California.

California Weather Outlook: Northern and central California can expect one more round of precipitation, starting on Friday, Dec. 19. Starting this weekend, however, the focus for heavy precipitation will shift into the Northwest. As a result, the last ten days of December appear likely to be rather warm and dry across most of California, although showers may occasionally graze the northern part of the state.

The next regularly scheduled issuance of the emailed U.S. drought update will be Thursday, Jan. 8, 2015, unless conditions warrant an earlier release. The “U.S. Crops in Drought” products are online:
http://www.usda.gov/oce/weather/Drought/AgInDrought.pdf

Archived “U.S. Crops in Drought” files:
http://drought.unl.edu/Planning/Impacts/USAginDroughtArchive.aspx

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