Weather Watch

Central Coast summers offer extremes in temperature

A cooling marine layer hovers over Port San Luis.
A cooling marine layer hovers over Port San Luis.

As the Central Coast moves toward summer, the temperature differences between the shoreline and the interior become very noticeable. It’s not unusual to see triple-digit temperatures in the North County or even in the coastal valleys, while the meteorological tower at Diablo Canyon nuclear power plant along the coastline is reporting temperatures in the 50s.

That’s what occurred Friday when Paso Robles Municipal Airport reached 105 degrees at 4 p.m., while Diablo Canyon reported 57 degrees — a nearly 50-degree temperature difference between the shoreline and the inland valleys.

Tribune journalist Kathe Tanner reported a “thermal whiplash driving from Templeton to Cambria,” she told me.

Not only do we experience severe temperature differences in the horizontal plane, but also in the vertical direction. This is called a temperature inversion when a warmer, less dense air mass covers cooler, denser air at the surface.

On Friday, the PG&E Black Butte weather station on the Cuesta Grade (at an elevation of 2,600 feet) reported a temperature of 83 degrees at 5 a.m. At the same time, the San Luis Obispo County Farm Bureau Weather Station at 240 feet of elevation reported a temperature of 66 degrees. A weather balloon launched from Vandenberg Air Force Base on Friday, indicated a 55-degree air temperature at sea level and quickly warmed to 87 degrees when it reached 2,800 feet.

I’ve experienced temperature gradients of more than 40 degrees in less than a few miles while traveling Highway 101 from Avila Valley toward San Luis Obispo. The temperature changes were because of cool moisture-laden northwesterly (onshore) winds from the Pacific Ocean blowing through Los Osos Valley while hot and dry Santa Lucia northeasterly (offshore) winds moved from 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. Thankfully, along the Central Coast, 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 hot days.

The greatest temperature gradient along the Central Coast I know of occurred on Sunday, Sept. 2, 2007. It was Labor Day weekend, and at the Pops by the Sea concert in Avila Beach, high pressure in the upper atmosphere combined with dry and hot Santa Lucia winds to produce scorching coastal temperatures. There were reports of thermometers reaching 110 degrees in Avila Beach that day.

I remember numerous concert attendees jumping in San Luis Creek to keep cool.

A little distance away, 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 farther out to sea, the temperature reached 60 degrees off the Point San Luis Lighthouse.

That’s what you call a temperature gradient. One could write an American Meteorological Society Bulletin about these temperature gradients, but many meteorologists from other parts of the country would probably be skeptical that such temperature differences could even occur.

As far as temperature dropping in a fixed location, I received a fascinating email that I treasure to this day from Tobias Brekke of San Luis Obispo who passed away last year. Tobias looked for the best in everyone and helped more souls than even he could ever imagine.

He was climbing Mount McKinley with a summit elevation of about 20,320 feet in Alaska’s Denali National Park back in June 1981. After five or six days of climbing, the temperature reached 80 degrees.

“Because of the heat, the mountain exploded with the biggest avalanche I had ever experienced, stopping just short of burying all of us,” he said. “There were ice blocks the size of shopping malls.”

They made camp and named it Coco Beach Camp because of the amazingly warm temperatures. After pitching camp, the winds began to blow. An intense storm reached their area and the temperature dropped to 65 degrees below zero in just a few hours. That’s a 145-degree temperature drop! Unofficially, that would be the greatest temperature change in less than 12 hours ever recorded in the United States — if not the world!

At PG&E, your safety is our highest priority. Summer is almost here, which means lots of fun in the sun. Nevertheless, the weather can get extremely hot and quickly go from fun to dangerous. Extreme heat can be life threatening. So learn what extreme heat is and how you can protect yourself. Please visit for heat safety tips.

John Lindsey is the PG&E Diablo Canyon meteorologist and media relations representative. Email him at or follow him on Twitter @PGE_John.