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If you live in California, you don’t often think of sandstorms, but they do happen. One of the worst occurred on Dec. 20, 1977, when a terrible dust and sandstorm struck the southern San Joaquin Valley and caused a great amount of damage.

That year, the Eastern Pacific high was entrenched off the California coastline and kept the storm track far to the north. This prevented all but a few weather systems from penetrating into California.

The most notable was Hurricane Doreen, which tracked northwestward along Mexico’s Baja Peninsula, came onshore as a tropical depression over Orange County and produced heavy rain and floods in parts of Southern California.

Otherwise, the position of the Eastern Pacific high produced one of the worst two-year droughts in California history, from 1975 through 1977. The San Joaquin Valley was declared a disaster area. Its soils were more parched than normal. The snowpack measurements performed on April 1, 1977 indicated the lowest water content in 47 years. As the winter of 1977 approached, the air over the high deserts of the western United States cooled and became dense.

On Dec. 20, an exceptionally strong area of high pressure moved southward over the Great Basin. At the same time, an intense low-pressure system and its associated cold front approached the coast of Northern California. This condition produced a very steep pressure gradient through the Central Valley. The air flowed in a clockwise direction around the high pressure system, forcing cool and dry desert air down the Tehachapi mountain canyons toward the southern San Joaquin Valley. As gravity pulled the air mass toward the valley floor, it funneled through the mountain passes and canyons, producing hurricane-force east-southeasterly winds. To make matters worse, as this air mass descended, it was compressed, and its temperature increased; as air heats, its relative humidity decreases, so the air became bone dry.

Fearsome winds slammed into the southern San Joaquin Valley that day and, combined with the extraordinarily dry soil, produced a terrifying dust and sandstorm.

Vehicles that were left outside during that sandstorm were literally sandblasted. The winds carried tremendous amounts of soil that filled in many of the water canals that criss-crossed that part of the valley. It took weeks of work by heavy equipment operators to clear some those canals. Not surprisingly, large volumes of dust were carried northward through the San Joaquin and Sacramento valleys toward the Oregon border. Dust from this storm obscured the sun as far north as Colusa County. Months later, PG&E hydrographers found a layer of dust embedded in the snowpack in Mount Shasta.

An outbreak of valley fever followed as spores traveled into Sacramento and Redding. A great ape at the San Francisco Zoo succumbed to the fever.

Did you know? PG&E delivers some of the nation’s cleanest power. Nearly 70 percent of the electricity the company provides to customers comes from sources that are renewable and/or emit no greenhouse gases.

John Lindsey is Pacific Gas and Electric Co.’s Diablo Canyon Power Plant marine meteorologist and a media relations representative. Email him at pgeweather@pge.com or follow him on Twitter @PGE_John.

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