I am often asked, “About what time of day do we usually have our highest temperatures in different parts of the Central Coast? Is the warmest hour of the day different during summer or winter?”
As the sun rises, the solar radiation increases until the sun is at its highest point in the sky at noon Pacific Standard Time or 1 p.m. daylight saving time. This is called solar noon. Even though the sun’s radiation is at its strongest then, that doesn’t necessarily mean that the maximum temperature will occur at that time.
Many inland areas of San Luis Obispo County will continue to climb so long as the earth is receiving more incoming heat than what is radiating back to space. On average, the summertime temperature will actually peak at 3:30 p.m. in Paso Robles. Farther inland, Bakersfield doesn’t peak until 5 p.m. during the summer months. The delay between maximum solar radiation and the warmest time of the day is called thermal response. In fact, by the time the surface temperature reaches its maximum in the San Joaquin Valley, the amount of solar radiation reaching the surface has decreased almost by half of that at solar noon.
However, it’s a different story along our rugged coastline. We live in an area of many microclimates. Tribune journalist Kathe Tanner reported a “thermal whiplash” driving from Templeton to Cambria on Highway 46 West.
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. Last week, for 48 hours, overnight temperatures on top of the Santa Lucia Mountains above Cambria never dropped below 80 degrees, while along the shoreline; temperatures dropped to the low 50s.
These temperature changes are often caused by the northeasterly Santa Lucia (offshore) winds and northwesterly (onshore) winds that often clash with each other for supremacy. This back-and-forth battle can produce hot conditions in the late morning and then cool conditions in the afternoon in Cambria.
That’s why a lot of us keep a sweater handy. For example, San Luis Obispo will typically reach its highest daily summer temperature at 2 p.m. before the northwesterly (onshore) winds kick in to drive the temperature down. On average, Cambria reaches its maximum temperature at 11 a.m. with the morning’s Santa Lucia winds.
During the winter months, the coastal areas reach their maximum temperature later in the day, while the inland areas hit their highs earlier.
A similar pattern occurs on a seasonal level. The sun’s radiation is at its greatest for the entire year at the summer solstice — the longest day of the year. Our atmosphere is a lot like a large freight train; it takes a lot of energy to get it going. This year’s summer started June 20. However, the warmest months in San Luis Obispo County will not occur until August through September. Seawater temperatures also greatly influence our air temperatures, which peak along the coastline in late September through October.
At PG&E, your safety is our highest priority. Summer is 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 www.pge.com for heat safety tips.
John Lindsey is the PG&E Diablo Canyon meteorologist and media relations representative. Email him at firstname.lastname@example.org or follow him on Twitter @PGE_John. His column appears quarterly and is special to The Cambrian.