At 8:09 p.m. today, the sun will be directly above the Earth’s equator, resulting in the end of summer and the beginning of fall. As we move into autumn, the days will continue to get shorter and have less sunlight and cooler temperatures. But this past summer wasn’t normal, and relatively speaking, we will probably see warmer temperatures this fall than what we experienced this summer in the coastal valleys and along the beaches.
Santa Barbara recorded its coldest summer since record-keeping began in 1941. Normally, the average temperature for the summer is 64.7 degrees. But this year, the average was only 61.9 degrees, according to National Weather Service meteorologist Eric Boldt in Oxnard.
San Luis Obispo usually averages 66.3 degrees during summer, but this year, it averaged 62.8 degrees. Santa Maria had the sixth coldest summer on record, averaging 59.8 degrees. Normally it is 62.8 degrees for the summer.
Temperatures were even cooler at the beaches near San Luis Obispo. For the majority of summer, the air temperature at the Diablo Canyon nuclear power plant never even reached the 60-degree mark, remaining in the 50s under mostly overcast skies. Most locations in coastal California averaged 3 to 8 degrees cooler than average this summer.
So what happened to summer? It was a combination of several factors.
The jet stream buckled over the West Coast, producing a series of upper-level, low-pressure troughs along the coastline. The troughs decreased the amount of subsidence, or sinking of the air mass, that normally occurs during the summer. That, in turn, allowed a deeper marine layer to develop and persist.
Also, persistent northwesterly winds produced an unusually great amount of upwelling and, combined with a strengthening La Niña (colder than normal ocean water in the equatorial and eastern Pacific), helped to produce unusually chilly seawater temperatures along the immediate shoreline, cooling the air above it.
Another factor was the near total lack of monsoon moisture. In the past, I’ve seen this cycle of low coastal clouds broken when subtropical moisture from the south migrates across our area. This moisture often mixes out the marine layer and can cause our Mediterranean climate to change to a humid, subtropical one reminiscent of Florida. But there were no thunderstorms this summer.
Warmer weather could be on the way. Typically during the fall, an area of high pressure builds at the surface over the Great Basin — the area between the Sierra Nevada range to the west and the Rocky Mountains to the east — and begins to dominate our coastal weather.
This condition usually produces northeasterly (offshore) winds, especially during the night and morning hours. These winds bring the relatively dry air to our shoreline, pushing the marine layer far out to sea, which produces sparkling, clear visibility along our beaches and warmer temperatures.
We will see immediate impact: Building high pressure will mean clear skies and hot temperatures Friday, with Paso Robles near 91 degrees and San Luis Obispo near 86.
It will get even warmer Saturday, with the high temperature near 100 in Paso Robles and near 90 in San Luis Obispo. Sunday stays hot before a cool down begins Monday.