Weather Watch

Bring the heat: California — and the entire nation — in for a hot, hot summer

Special to The Tribune

I made the assumption after three straight years of record-breaking air temperatures in Central California that this year would be cooler than normal due to the neutral condition — the infamous El Nothing or El Nada currently present in the central equatorial region of the Pacific Ocean.

The neutral condition combined with near- or below-average seawater temperatures along the California coastline caused by stronger than typical springtime northwesterly winds led me on the wrong path to my hypothesis. I also received emails from readers who asked about the lack of triple-digit readings in the inland valleys of the Central Coast; I thought that air temperatures were probably cooler than normal this spring.

I stand corrected after I carefully reviewed air temperature data from the National Weather Service’s Airport Surface Weather Observation Stations at San Luis Obispo, Paso Robles and Santa Maria. It turns out, air temperatures were warmer than average for the spring.

San Luis Obispo saw an average temperature of 62.6 degrees Fahrenheit, while Paso Robles reported 65.3 degrees.

That was between 2 and 2 1/2 degrees warmer than seasonal norms. Santa Maria recorded an average of 59.1 degrees, which was 1 degree warmer than normal for May.

So far, June is also above normal. And the difference between seasonal norms and actual temperatures will probably significantly increase for the rest of June, and here’s why.

A prolonged heat event, especially across the interior of San Luis Obispo and Santa Barbara counties, will persist through next week. As if on cue, on the first day of summer, Paso Robles is forecast to reach 107 on Tuesday and Wednesday, which may come close to breaking the daily high temperature for those days. Further inland, Bakersfield is forecast to hit 113 on Tuesday, which would break the previous record of 107 degrees recorded in 1947. Caused by a strong upper-level ridge of high pressure (596 dm) over the desert southwest that will expand and strengthen over California, it will allow temperatures to soar away from the coastline.

So what is dm? It’s an abbreviation for decameters.

On average, half of the atmosphere’s weight lies between the Earth’s surface and an altitude of about 18,000 feet.

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 atmosphere is at its thickest near the equator and gradually narrows toward the poles.

The higher the 500-millibar line, the thicker the atmosphere, and the warmer it will be.

Last week, the 500-mb line was around 577 decameters (dm) above the Earth and centered over the Central Coast.

Anything above 580 dm will usually provide hot temperatures in late spring, summer and fall. If you’re above 590 dm, there’s a possibility of record-breaking temperatures.

At the Earth’s surface, meteorologists often express air pressure in units called millibars (mb). The standard atmospheric pressure is defined as being equal to 1,013.25 mb at sea level. Depending on the surrounding atmospheric conditions, levels above that value may be considered areas of high pressure. Along the Central Coast, 1,030 mb and above is considered strong high pressure.

As the state heads into summer, the latest guidance from the U.S. Climate Prediction Center is calling for “above-normal temperatures” for all of California through September. In fact, they’re calling for above average temperatures throughout most of the United States.

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Please be careful if you’re heading to the Sierra Nevada this summer. Near- to record-breaking temperatures this week across much of California combined with one of the deepest snowpacks in the state’s history and record rainfall in many parts of the Sierra Nevada has produced colder and much higher river and stream flows.

California State Parks Division of Boating and Waterways (DBW) and PG&E warn water enthusiasts that river flows are expected to last longer and be greater than they have in years. Swift water can create treacherous conditions for all recreationists — waders, swimmers, paddlers, boaters, anglers and hikers cooling off at the water’s edge.

Enthusiasts are encouraged to take extra precautions when in or near the water.

“With the most snowmelt in decades, we ask those enjoying the outdoors to be careful near mountain streams, rivers and reservoirs. Water flows can fluctuate as the snow melts faster on warmer days, so always be prepared for a change in conditions,” said Ed Halpin, PG&E’s senior vice president of generation and chief nuclear officer.

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 pgeweather@pge.com or follow him on Twitter @PGE_John.

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