Living in the Goldilocks Zone

Relatively warm seawater, many sunny days and a frequent offshore air flow mean most Central Coast residents live in the Goldilocks Zone, but meteorologists have a formula for numerically quantifying and predicting how we'll respond to our climate in terms of energy demands.

Most of the Central Coast resides in the Goldilocks Zone, not too cold and not too hot but about just right.

One way to tell is to look at how often we turn on our air conditioners compared with other parts of the state.

When the mean daily temperature climbs above 65 degrees Fahrenheit, most people in the United States will begin to cool their homes and businesses.

I know 65 degrees sounds surprisingly low, but many years of historical temperature data and people’s behavior verifies the temperature.

Higher humidity levels in other parts of the country probably play an important part in determining that temperature.

“Cooling Degree-Days,” or CDD, is the term for the method used to estimate the energy needed to cool the atmosphere in our homes or businesses to 65 degrees.

In other words, CDD is used to relate the day’s mean temperature — the average temperature over a 24-hour period — to the energy demands of air-conditioning.

CDD is calculated by subtracting 65 degrees from the mean. The higher the CDD value, the greater amount of energy needed for cooling.

For example, a daily mean temperature in Santa Ynez of 70 degrees would produce 5 CDDs, or 70 degrees minus 65 degrees.

Pacific Gas and Electric Co.’s meteorologists forecast the daily mean temperature throughout its immense service territory, which extends from near the Oregon border, east toward Lake Tahoe and all the way south to the Gaviota Pass in Santa Barbara County.

By calculating the CDDs, PG&E can forecast energy demand and generate or buy the correct quantity of energy needed to keep us comfortable.

You can also use that value to compare the heat in different parts of the state.

Along the coastline in Northern California, persistent onshore winds and a cold Pacific Ocean often produce a deep and persistent marine layer.

That condition allows a blanket of fog to form over Eureka that greatly diminishes the amount of sunshine that reaches the ground for days on end during the summer.

The dreary and cool overcast gives Eureka a CDD of zero. Not a lot of need for air-conditioning in Eureka.

As you head farther south down the rugged Northern California coastline, Fort Bragg has a CDD of 6, and San Francisco, with slightly warmer seawater temperatures, has a CDD of 108.

As you continue to move toward the more southern latitudes of the Central Coast, occasional offshore wind events produce higher CDD levels. Santa Maria has a CDD level of 456, while Lompoc has a CDD level of 332.

I couldn’t find any official values for Santa Ynez Valley communities, but I suspect they would be higher due to the greater amount of sunshine and warmer temperatures at those locations.

Once you pass Point Conception, the Pacific Ocean abruptly warms. The warmer water and the hot and dry offshore Santa Ana winds produce a CDD of 984 at San Diego.

Heading toward the interior where even more sunshine reaches the surface, the CDD is 956 in Paso Robles.

Fortunately, night and morning marine stratus often streams southward from the Salinas Valley and through the Templeton Gap, allowing homes to cool naturally at night, which reduces the need for air-conditioning.

The same can’t be said for the low desert of far Southern California, which is characterized by extremely hot days and warm nights during the summer when the sun’s rays relentlessly heat the Earth’s surface and cooling is the overwhelming concern.

Brawley in Imperial County has the highest CDD that I could find in the state at 6,565. Living in Brawley would probably require the air conditioner to be on almost continuously during the summer.

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Where does Pacific Gas and Electric Co. procure the energy to meet the requirement of all those CDDs?

In 2017, nearly 80 percent of the electricity the utility provided to customers came from sources that are renewable and/or emit no greenhouse gases.

John Lindsey is Pacific Gas and Electric Co.’s Diablo Canyon Power Plant marine meteorologist and a media relations representative. Follow him on Twitter @PGE_John.


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