Powerful onshore winds make for blustery spring days

Special to The TribuneApril 26, 2014 

Gale-force northwesterly winds blow across Morro Bay last week.

COURTESY PHOTO

True to its nature, the northwesterly (onshore) winds of spring have returned along the Central Coast. Spring is a transition season in terms of weather conditions: not quite summer and not quite winter.

You may have stormy weather one day followed by record-breaking heat the next. However, spring along the Central Coast usually means constant northwesterly winds.

To put the wind direction into perspective, at this time of the year, the winds blow out of the northwest around 80 percent of the time at the Diablo Canyon nuclear power plant’s meteorological tower.

If these winds are strong enough, they make a howling noise as they travel over tower’s guide wires. In old weather reports from the early 1900s in San Luis Obispo, locals often called these winds the “Los Osos winds” as they blew in from the Los Osos Valley off the Pacific Ocean.

So why is spring so windy? At this time of the year, the Eastern Pacific High off the California coast strengthens and gradually shifts northward.

This condition frequently weakens cold fronts as they head down the California coastline, which diminishes the strength of the pre-frontal (southerly) winds, but tends to increase the post-frontal (northwesterly) winds.

The northwesterly winds of spring are further enhanced by the greater amount of sunlight as the days grow longer. Let me explain, the longer days produce warmer temperatures in the inland valleys.

As the valley’s surface air is warmed, it expands and rises like a hot air balloon. This in turn, produces lower pressure at the earth’s surface. Meteorologists refer to this as a thermal low.

Nature never likes anything out of balance, and consequently, the higher air pressure out over ocean forces air inland in to fill the void left by the thermal low.

As these northwesterly winds blew along the coastline, the friction of the wind causes the ocean surface water to move.

The apparent Coriolis force turns the surface water to the right, or offshore, causing upwelling along the shoreline as very cold and nutrient-rich subsurface water ascends to the surface along the beaches. At times like these, seawater temperatures can plummet to a bone-chilling 48 degrees!

As the winds blow across these cold seas, they are cooled like a gigantic air conditioner. Not only are these winds cold, but thankfully they are almost free of pollen along the coastline.

The number of people affected by pollen is staggering — doctors estimate between 10 and 30 percent of the adult population has hay fever, with the numbers even higher in children.

The medical community will tell you that hay fever – seasonal allergic rhinitis, or SAR, is the correct term because hay is not usually the problem – is frequently caused by pollen.

If you suffer from hay fever, the nearly pollen-free onshore winds usually keep the pollen counts low at Montaña de Oro State Park, Los Osos, Morro Bay and other northwesterly-facing beach communities.

However, as these winds travel inland, they pick up small, light, dry pollen grains from grasses, trees and weeds, and invisibly spread them across the coastal valleys toward the interior. This condition increases the inland pollen count, and by the time it reaches San Luis Obispo you may be sneezing.

In honor of National Volunteer Month this month, PG&E has announced an unprecedented employee volunteerism goal for the company of 50,000 employee volunteer hours this year. This goal is supported by the company’s Month of Service program, which will feature more than 100 employee volunteer projects throughout Northern and Central California.

John Lindsey’s column is special to The Tribune. He is a media relations representative for PG&E and a longtime local meteorologist. He is president of the Point San Luis Lighthouse Keepers. If you have a question, send him an email at pgeweather@pge.com.

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