Weather Watch

Week’s winds were tough, but look at ’77

I knew it was bad when I saw the photographs of overturned semitrailers near Cajon Pass in San Bernardino County. I was stunned to see concrete light poles cracked in half by the wind’s force in Los Angeles County.

Most of the time, Central Coast surfers, kayakers and beachgoers lovingly anticipate the arrival of the northeasterly (offshore) winds with the warmer temperatures and sparkling clear skies they often bring. During late fall and winter, coastal temperatures will often be warmer than the inland temperatures in the North County. However, like many things in life, too much of a good thing can be bad. So it was last week with a strong offshore wind event.

Winds are caused by air flowing from high pressure to low pressure, like air escaping from an inflated balloon. When an area of high pressure moves closer to a region of low pressure, the differential gives rise to stronger winds.

Weather charts show lines of constant pressure as isobars. These black isobar lines that curve across weather maps are labeled with their pressure value in millibars (mb). The closer these lines are together, the stronger the wind.

Wednesday night and Thursday, the isobars were spaced very close together along the entire length of California, producing one of the fiercest wind events in Southern California in many years. These frightful Santa Ana winds knocked down trees and left hundreds of thousands of people without power.

Laurel Mountain at 4,390 feet in Kern County reported sustained northerly winds of 68 mph with gusts to 89 mph. A wind gust of 97 mph was recorded at the 4,120-foot Whitaker Peak in Los Angeles County on Wednesday night. Mammoth Mountain Summit at 11,053 feet had sustained winds of 140 mph with gusts above 150 mph.

At this high altitude, the jet stream was significantly contributing to these amazing wind speeds.

Closer to home, the SLOweather.com   weather station on top of the Condor Lookout facility, located at an elevation of 3,190 feet on aptly named Hi Mountain about 15 miles east of San Luis Obispo, reported sustained winds of 55 mph with gusts to 63 mph.

State Parks officials decided to cancel tours at Hearst Castle because they were worried about visitors being struck by falling tree debris. Falling trees and debris produced widespread power outages in Cambria.

One of the strongest California wind events that I know of occurred during winter 1977. On Dec. 20, an exceptionally strong area of high pressure moved southward over the Great Basin, the expanse of land between the Sierra Nevada range to the west and the Rocky Mountains to the east.

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.

Some of the strongest winds ever recorded in California history slammed into the southern San Joaquin Valley that day and, combined with the extraordinarily dry soil, produced a fearsome dust and sand storm.

Sustained winds reached 125 mph and caused extensive damage to buildings and fertile farmland. The U.S. Geological Survey estimated that wind gusts reached 192 mph at Arvin! Cliff Trotter, who was the engineer-manager of the Arvin-Edison Water Storage District in Kern County at the time, told me that “Vehicles that were left outside during that windstorm were literally sandblasted.”

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.

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. Months later, PG&E hydrographers found a layer of dust embedded in the snowpack in the Mount Shasta area that was probably from this event. Thursday.

Another round of gentle to moderate (8- to 18-mph) northeasterly (offshore) winds is forecast Friday through next weekend.

The long-range models keep the Central Coast dry until about the middle of December if not longer.

Today’s forecast

Monday afternoon will see increasing southerly (onshore) winds that will produce higher humidity levels and warmer overnight lows along the beaches and coastal valleys Tuesday.

Moderate to fresh (13-to 24-mph) northwesterly (onshore) winds Wednesday and Thursday will give even warmer overnight lows and areas of low clouds and fog along the beaches and coastal valleys Wednesday night into

Surf report

Today’s 4- to 6-foot northwesterly (300-degree deepwater) swell (with a with an 11- to 13-second period) will decrease to 3 to 5 feet (with an 8- to 11-second period) Monday and will remain at this height and period through Tuesday.

Increasing northwesterly winds will generate a 2-to 4-foot northwesterly (310-degree deep-water) sea and swell (with a 5- to 15-second period) Wednesday and Thursday.

A 960-millibar storm with hurricane force winds off Russia’s Kamchatka Peninsula will produce a long-period westnorthwesterly swell. This swell will arrive along the coast Friday at 3 to 5 feet (with an 18- to 20-second period), building to 4 to 6 feet (with a 16- to 18-second period) Saturday.

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John Lindsey is a media relations representative for PG&E. He is also a local weather expert and has lived along the Central Coast for nearly 25 years. Email him at pge weather@pge.com.

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