John Lindsey: SLO County’s battling microclimates

We live in a county with many microclimates, which become especially prevalent during the late summer and early fall months.

During this time, the northeasterly (offshore) winds and northwesterly (onshore) winds battle it out for supremacy.

The back-and-forth battle can produce hot temperatures in the late morning and then cool temperatures in the afternoon — in the same locations. That’s why a lot of us keep a sweater handy.

The wind direction is reported from where the wind originates. The wind direction is usually reported in cardinal headings.

For example, northeasterly winds are from the northeast and blow toward the southwest.

Because of compressional heating as these winds descend the Santa Lucia Mountains, they can become hot and dry as they move out to sea.

On the other hand, the cool and moisture-laden northwesterly winds come off the Pacific Ocean and blow southeast to land.

Last month I took a drive along Highway 101 from Avila Valley toward Los Osos Valley Road. In just a few miles, the outside temperature gauge on my car went from the low 100s through the Avila Valley to the low 60s as I reached Los Osos Valley Road.

The temperature changes were because of cool northwesterly winds from the Pacific Ocean blowing through the Los Osos Valley, while at the same time the hot and dry northeasterly winds were coming off the Santa Lucia Mountains through Avila Valley.

Many thermometers on today’s automobiles are not fast enough to keep up with such severe temperature changes.

Other passes along the coastal range, such as the Templeton Gap, allow the cool marine air to filter into the coastal valleys and interior, giving relief on the hot days.

Not only do we experience severe temperature gradients in the horizontal plane but also in the vertical direction.

Last Saturday morning, a weather balloon was launched from Vandenberg Air Force Base. The air temperature at sea level was 49 degrees Fahrenheit and quickly warmed to 91 degrees by the time the balloon reached 2,100 feet!

One of the county’s special places is Avila Beach, because its southeasterly orientation along the coastline.

Both northwesterly and northeasterly winds often blow offshore there. That’s why it’s often the sunniest beach in the county.

Two years ago at Pops by the Sea in Avila Beach, it was especially hot. A fishing boat at Port San Luis reported a temperature of 105 degrees near the Harford Pier.

As the boat moved past the breakwater toward the wind shift line, the temperature dropped 37 degrees in less than a quarter mile.

About a half mile further out to sea, the temperature reached 60 degrees. That’s what you call a temperature gradient!

This week’s forecast

A cold front associated with the low-pressure system over Nevada passed our area last night, leaving behind a steep pressure gradient.

This condition produced moderate-gale-to-fresh-gale-force (32 to 46 mph) northwesterly winds along the immediate coastline Saturday night through early this morning.

These northwesterly (onshore) winds will usher in areas of coastal low clouds, fog and drizzle this morning and much cooler temperatures throughout our area.

By this afternoon, we should see partly cloudy to mostly clear conditions. Today’s temperatures will only reach the 60s across most locations and possibly 70-degree readings in a few locations across the interior, making it feel a lot like late fall.

A gradual warming trend will begin Monday and will continue through most of next week as gentle north to northeasterly(offshore) winds develop during the morning hours.

These winds will produce a greater amount of sunshine and fewer coastal low clouds and fog.

However, temperatures will remain under seasonal norms.

The longer range charts are indicating that a chance of unsettled weather is developing for the following week.

Surf and sea report

Moderate-gale to fresh-gale-force (32 to 46 mph) northwesterly winds along the Northern and Central California coastline have produced 9- to 11-foot northwesterly (310-degree deep-water) sea and swell (with a 4- to 12-second period) along our coastline this morning.

This northwesterly sea and swell will continue at this height and period through this afternoon, decreasing somewhat tonight.

Note: This combined northwesterly sea and swell heights will be higher at the offshore marine buoys.

This northwesterly sea and swell will decrease to 5-to 7-feet on Monday, becoming a 3- to 5-foot northwesterly (290-degree deep-water) swell (with an 8- to 11-second period) on Tuesday.

A 3- to 4-foot northwesterly (300-degree deep-water) sea and swell (with a 5-to 13-second period) will develop along our coastline on Wednesday and will continue at this height and period through Saturday.

Arriving from the southern hemisphere:

Today’s 2- to 3-foot southern hemisphere (195-degree deep-water) swell (with a 16-to 18-second period) will continue at this height but with a gradually shorter period through Wednesday.

Seawater temperatures will range between 55 and 57 degrees through Monday, gradually increasing on Tuesday through Friday.

Conservation tip

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John Lindsey is a media relations and nuclear communications representative for Pacific Gas and Electric Co. He is also a meteorologist who specializes in forecasting for San Luis Obispo County. Send him questions to pgeweather@pge.com.