Weather Watch

Extreme microclimates along the Central Coast are becoming the new norm. Here’s why

A Catalina Eddy is forecast to develop Sunday into Tuesday, which will produce decreasing northwesterly winds and cause the marine layer to deepen and move further inland during the night and morning hours with pockets of fog and drizzle throughout the coastal regions of San Luis Obispo and northern Santa Barbara counties.
A Catalina Eddy is forecast to develop Sunday into Tuesday, which will produce decreasing northwesterly winds and cause the marine layer to deepen and move further inland during the night and morning hours with pockets of fog and drizzle throughout the coastal regions of San Luis Obispo and northern Santa Barbara counties. Special to The Tribune

An epic temperature gradient developed along the Central Coast on Wednesday.

At 2 that afternoon, Diablo Canyon Power Plant reported 55 degrees Fahrenheit, while just a few miles away, the PG&E Energy Education Center in Avila Valley was at 108 degrees. That’s a 53-degree temperature differential. I went through my records, and I couldn’t find such a drastic temperature differential between the two locations.

Think about that: For the unprepared, 108-degree temperatures could lead to heat exhaustion turning to heatstroke, which is classified as a medical emergency. Conversely, and depending upon the person, 55-degree conditions can cause hypothermia.

Previously, the most significant temperature gradient along the Central Coast I know of occurred on Sunday, Sept. 2, 2007. It was Labor Day weekend when at the Pops by the Sea concert in Avila Beach there were reports of thermometers reaching 110 degrees. A little distance away, a fishing boat at Port San Luis reported a temperature of 105 degrees near the Harford Pier. As the vessel moved past the breakwater toward the wind-shift line, the temperature dropped 37 degrees in less than a quarter mile.

Yes, the Central Coast is a land of many microclimates, but lately extreme microclimates seem to be a more accurate description. Bob Shanbrom of San Luis Obispo said it best: “Sometimes you need to have the air conditioning on in the front of your car and the heater in the back.”

In other parts of the country, especially in Gulf of Mexico regions, you could drive for hundreds of miles in summer and only experience a few degrees of temperature change.

So why do specific Central Coast locations experience such drastic temperature differentials?

Well, there were a lot of moving parts occurring Wednesday. First, the northwesterly winds nearly reached 50 mph at the Diablo Canyon Power Plant’s meteorological tower. This, in turn, produced enormous amounts of upwelling, which brought 51-degree seawater temperatures to the immediate coastline that chilled the air above and created low marine clouds.

Secondly, a massive dome of high pressure in the upper atmosphere, kind of like Steven King’s “Under the Dome,” produced triple-digit temperatures away from the coastline throughout California. This condition also formed a strong temperature inversion layer. In fact, temperatures were in the high-90s about 1,500 feet above the shoreline on July 25.

This area of increasing air temperatures with rising height is referred to as subsidence inversion. Within this region, the air sinks (subsidence) and warms by compression, but it tends not to break through the relatively cooler and denser Pacific air mass.

However, if the northwesterly winds blow more than 40 mph over the Irish Hills, located west of San Luis Obispo, these gales can break through the inversion and bring this hot and dry air mass to Avila Valley; and that’s what occurred on Wednesday.

As the air mass descends, 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 or compressional heating, like a bicycle tire or scuba tank that’s being inflated. 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.

Not only do these severe temperature gradients occurred in Avila Valley, but in other coastal valleys near the coastline along the Central Coast. In the future, these temperature gradients will probably become greater and here’s why.

After review of data from the PG&E Diablo Canyon meteorological towers and other weather stations farther inland, I discovered that the temperature inversion layer is becoming stronger over the long-term.

You see, if you put a balloon filled with air over a flame, it will pop in an instant. However, if that balloon is filled with water, the liquid absorbs the heat, and it will not burst. Water’s thermal conductivity (the rate it can remove or add heat) is much higher than air and has four times the specific heat capacity than air, according to Cal Poly thermal dynamics professor Jim LoCascio.

This is one of the reasons why the atmosphere is warming at a faster rate than the Pacific Ocean as ever- increasing amounts of greenhouse gases are dumped into the atmosphere, like carbon dioxide, which acts as a blanket reducing the amount of heat that can radiate in the space. This, in turn, can fashion stronger inversion layers. The warming of the atmosphere is causing all sorts of problems, including more intense wildfires.

We can all help by reducing our carbon footprint. By far, the most prominent single contributor to greenhouse gases in California is transportation. Our family purchased an electric vehicle several years ago, which dramatically reduced the amount of carbon dioxide we put into the atmosphere every year.

The electricity we use to power our cars is clean. In 2015, the energy that PG&E delivered to our house was about 60 percent carbon-free. That number climbed to nearly 70 percent in 2016, and in 2017 it was 80 percent.

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.

Heading to the Mid-State Fair in Paso Robles this week? Brace yourself for triple-digit heat, and follow these tips on staying cool.

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