What shall we call these winds?

pgeweather@pge.comNovember 10, 2012 

Throughout the world, downslope winds have been given different names. Along the Rocky Mountains, these down-slope winds are known as Chinook — literally meaning “snow-eater” — winds. In Japan, they are called the Oroshi. Around the Adriatic Sea, they are referred to as the Bora winds.

In Southern California, these downslope winds are called the Santa Anas. These famous winds may have gotten their name from the Santa Ana Mountains. However, some Southern Californians believe that the traditional name is Santanas. That name was occasionally used in early reports. In Northern California, these downslope winds are called diablo winds. Even relatively small geographic areas will have their own unique name for these winds.

For example, in Santa Barbara, they’re referred to as “sundowners.” “The Barber” winds blow over the town of Greymouth in New Zealand.

Like an old International Harvester semi-truck rolling down the Cuesta Grade, air from the higher elevations of the Santa Lucia Mountains will flow downward along the mountain slopes toward the Pacific Ocean, pulled by the never-ending force of gravity.

These are often referred to as downslope or lovingly described by surfers as offshore winds. However, these downslope winds are technically called katabatic wind, from the Greek word katabatikos, which means “going downhill.”

As the air mass descends the side of the mountain range, it warms at the rate of about 5.5 degrees Fahrenheit per 1,000 feet of descent. Meteorologists refer to this rate of warming as the dry adiabatic lapse rate. If the air is warm at the top of the mountain range, it can be sizzling hot and bone dry by the time it reaches the valleys below.

You see, as the air molecules descend into the higher atmospheric pressure close to Earth’s surface, they gain kinetic energy as they compress inward. If you’ve ever filled up a bicycle tire or especially a scuba tank, you’ve probably noticed them getting warmer as the pressure increased. This is
also referred to as compressional heating.

A large ridge of high pressure parked itself over California last week and produced night and morning northeasterly (offshore) winds. These downslope winds along with subsidence, or sinking of the air mass over the county, created the warmest beach weather of the year. Old high
temperature records fell like bowling pins this past Monday and Tuesday.

When these northwesterly (offshore) winds blow, temperatures at our beaches often peak during the late morning hours before the afternoon northwesterly (onshore) winds cool things off.

Historically, wind data recorded at the Diablo Canyon meteorological tower indicates that northeasterly winds blow about 12 percent of the time throughout the year, but during the fall this percentage can increase to more than 20 percent.

Autumn is often the warmest season along our beaches because of the greater occurrence of northeasterly (offshore) winds.

All this leads to an interesting question that Chris Arndt of SLOweather.com asked recently: Why doesn’t San Luis Obispo County have its own unique name for these downslope winds?

I don’t know the answer. But perhaps it’s finally time to name these winds. We could call them the Santa Lucia winds, or perhaps the Obispo winds. Maybe even the Cuesta winds.

If you have a suggestion, please write me an email at pgeweather@pge.com. After we get the suggestions together, Chris will post them on SLOweather.com and give everyone a chance to vote for their favorite.

If you don’t have email, please write to John Lindsey, PG&E, P.O. Box 56, Avila Beach, CA 93424-0056.

Historically, the only winds I found that had a name in San Luis Obispo County were the Los Osos winds. Depending on the time of the year, these northwesterly (onshore) winds blowing from the Pacific through the Los Osos Valley toward San Luis Obispo could either produce cooling sea breezes during a hot summer afternoon or bitterly persistent icy temperatures with fog during the spring.

After last week’s heat wave, I’m sure a lot of us will welcome back the large white blanket of the coastal fog monster and the cooler conditions that these Los Osos winds bring.

Today’s weather report

This Veterans Day morning will see gentle to moderate (8- to 18-mph) northeasterly (offshore) winds in the coastal valleys and along the beaches.

These downslope winds will keep the coastal valleys and beaches above freezing. However, locations sheltered from these winds in the North County could see morning low temperatures drop into the low to mid-20s. Very cold indeed.

Temperatures will rise to the low to mid-60s throughout San Luis Obispo County this afternoon.

An area of high pressure will continue to build over California in the wake of Friday’s weather system.This condition will produce fresh to strong northeasterly (offshore) winds during the night and morning hours Monday and especially Tuesday.

In fact, wind gusts of nearly 50 mph could develop in the coastal canyons and passes during the morning hours. Areas near Morro Bay High School and eastern San Luis Obispo will be particularly windy.

These winds will produce dry and clear conditions Monday into Wednesday, with afternoon temperatures reaching the mid-70s in the coastal valleys and along the beaches.

But once again, areas sheltered from these winds in the North County will see overnight lows drop into the mid-20s.

Another Gulf of Alaska low-pressure system is expected to produce increasing southeasterly winds beginning Wednesday evening and continuing through Friday. The associate cold front is forecast to past over the Central Coast on Thursday night into Friday, producing rain showers.

At this time, rainfall amounts do not appear heavy. On the other hand, temperatures are not expected to be nearly as low as those that accompanied the most recent system. Unsettled weather is expected next weekend.

Today’s surf report

The winds will shift offshore today. Consequently, the northwesterly (295-degree deep-water) swell will decrease to 3 to 5 feet (with an 8- to 11-second period) later today and will remain at this height and period through Wednesday.

Increasing southerly winds will generate 2- to 4-foot southerly (180-degree shallow-water) seas (with a 4- to 7-second period) Thursday, increasing to 3 to 5 feet Friday.

A 970-millibar Gulf of Alaska storm will produce a 3- to 5-foot northwesterly (300-degree deep-water) swell (with an 18- to 20-second period) Friday, increasing to 5 to 7 feet (with a 16- to 18-second period) Saturday.

Seawater temperatures

Seawater temperatures will be between 56 and 58 degrees through Tuesday, increasing to 57 to 59
degrees Wednesday through Saturday.

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

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