Weather Watch

Think it’s going to get hot in SLO County? Heat records are being broken across the world

A heat wave is classified as a prolonged period of extremely high temperatures for a specific region or season.

But what is a heat wave in one region can be called normal for another area. You see, if our coastal communities reached into the 80s over a few days, it would be classified a heat wave, while just a short distance away in the inland valleys it would be considered cool at this time of year.

Yes, the Central Coast is a land of many microclimates.

With that said, the inland valleys of California are in for a heat wave, perhaps a record-breaking one, which will start Monday and continue through Friday, if not longer, and here’s why.

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As I wrote earlier this year, the Climate Prediction Center forecasted “above-normal temperatures” for much of the United States this summer. So far, their prediction has been verified.

Not only has North America seen above-average temperatures, but also throughout the Northern Hemisphere. Much of Finland and Sweden that resides well within the Arctic Circle reached into the high 80s this past week. Kevo, Finland, located at the 70th parallel north, hit 91 degrees on Wednesday. Kevo is closer to the North Pole than nearly all of Alaska.

The ancient city of Kyoto, Japan, reported over a week of 100-degree or higher temperatures, smashing all their records. Early in July, Quriyat, Oman, recorded an overnight low of 108.7 degrees, the highest “low” temperature in world history.

Closer to home, the Electric Reliability Council of Texas said electrical demand reached 73,259 megawatts on Thursday, breaking their previous all-time demand due to record-breaking heat throughout Texas and neighboring states. To put that in perspective, the record demand in California is 50,270 megawatts, according to the California ISO.

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Unfortunately, the upper-level high-pressure system responsible for these scorching Texas temperatures will travel westward toward California and start to produce triple-digit temperatures in the inland valleys Monday.

Along the coastline, a steep pressure gradient will develop and produce gale-force northwesterly winds. These winds will keep temperatures in the coastal regions cooler with the daily highs occurring during the late morning hours before the onshore winds coming off the Pacific bring a refreshing and moist air mass to the coastal valleys during the afternoon and evening hours.

This dome of heat from Texas may reach nearly 600 decameters (dm) in height and will be centered over Central and Southern California by Wednesday.

Meteorologists determine the thickness of the atmosphere by analyzing 500-millibar upper-level charts. In other words, this chart will tell you how high the pressure is 3 or 4 miles above the Earth’s surface. The higher the 500-millibar line, the thicker the atmosphere, and the warmer it will be.

Anything above 580 dm will usually give hot temperatures; if near 600 dm, record-breaking. Both Wednesday and Thursday could see record-breaking temperatures in the inland valleys. The record high in Paso Robles for July 25 is 112 degrees set back in 2006, and the all-time high for July 26 is 109 degrees set in 1959.

As the atmosphere continues to warm due to increasing amounts of carbon dioxide and other greenhouse gases from the burning of fossil fuels, the thickness of these high-pressure domes will also increase which will bring an ever-greater number of heat waves.

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John Lindsey’s column is special to The Tribune. He is PG&E’s Diablo Canyon marine meteorologist and a media relations representative. Email him at or follow him on Twitter: @PGE_John.