With summer underway and a new rain season started, I thought it would be interesting to look at the long-range forecast for temperature and rain.
Central Coast summer temperatures
After a warmer than typical June, the first part of this July has been colder than usual.
So far, Paso Robles has seen an average temperature of 70.5 degrees; typically its 73.6 degrees. San Luis Obispo recorded an average temperature of 62.8 degrees or about 3 degrees below normal. Santa Maria reported a mean of only 61.5 degrees; historically its 63.2 in the month of July.
For the rest of July, temperatures are expected to remain slightly below to normal for most Central Coast locations. By the way, July 2018 saw well above-average temperatures for most areas away from the immediate coast.
Much like last August, temperatures this August are favored to be above average across the coastal and inland valleys and slightly above normal near the beaches. Last August, locations south of Point Conception were abnormally warm due to record-breaking local sea-surface temperatures. The Scripps Nearshore reached 81.3 degrees, breaking the old record 80.4 degrees set during the very strong El Niño event of 2015. The Torrey Pines waverider buoy also hit 81.3, while the Mission Bay buoy reported 79.9.
Temperatures in September are favored to be slightly above average across most of the inland valleys. The beaches and coastal valleys are expected to be near average, as well. September 2018 was slightly warmer for areas near the coast and colder across most of the interior.
Upcoming rainfall season outlook
Precipitation this July, August and September is expected to be near normal — or in other words, dry.
However, the North America Monsoon is expected to produce thunderstorms and rain over the Sierra Nevada with a typical chance of subtropical moisture reaching the Central Coast. For the rest of the season, the weak El Niño condition (warmer than usual ocean water in the equatorial and eastern Pacific), which helped to shift the position of the jet stream farther south, thereby directing more Pacific storms toward the Central Coast last winter (rainfall amounts in the previous season ranged from between 104 percent above average in Santa Ynez to 132 percent above normal at Cal Poly and SLOWeather.com).
However, according to the Climate Prediction Center, El Niño is predicted to persist through this summer (66 percent chance), but with lower odds of continuing through this fall and winter (50 to 55 percent chance). The neutral condition — the infamous “El Nothing” or “El Nada” — may develop by winter because of the increasing strength of the trade winds across the Pacific.
NOAA uses Niño 3.4, an area of sea-surface temperatures (SST) in a central equatorial region of the Pacific Ocean, as the standard for classifying El Niño (warmer-than-normal SST) and La Niña (cooler-than-normal SST) events.
The fortunetelling SST cycles in Niño 3.4 are categorized by the amount they deviate from the average SST over a three-month period. A weak El Niño is classified as an SST anomaly between 0.5 and 0.9 degrees Celsius. A moderate El Niño is an anomaly of 1.0 to 1.4 degrees Celsius. And a strong El Niño ranges from 1.5 to 1.9 degrees Celsius. A very strong El Niño anomaly is anything above 2.0 degrees Celsius (or 3.6 degrees Fahrenheit). The classification of the El Niño-Southern Oscillation (ENSO), or El Niño, La Niña or neutral conditions, historically has had a bearing on the amount of rainfall the Central Coast will receive.
Typically, in San Luis Obispo and Santa Barbara counties, the higher the classification of the El Niño event, the more rain it will create. On the other hand, La Niña events tend to produce less rain. Unfortunately, the predicted neutral conditions combined with another large-scale ocean water temperature cycle may produce lower-than-average winter rainfall.
The other large-scale ocean water temperature cycle is the Pacific Decadal Oscillation (PDO), which can increase or decrease the ENSO effect. The PDO is found primarily in the North Pacific. The phases of the PDO are called warm phases or cool phases. Unlike ENSO, which focuses on sea-surface temperature in the central equatorial region of the Pacific, the PDO is classified by seawater temperatures throughout the northern Pacific Ocean.
Josh Willis, oceanographer and climate scientist at NASA’s Jet Propulsion Laboratory in Pasadena, said the PDO shifted to the positive phase in late 2014, which historically enhances the effects of El Niño and La Niña events. However, some of the models are indicating that it will shift to the cool phase later this year, which means a higher chance of below-normal rainfall.
With that said, the predictions of ENSO conditions are often wrong. However, if the current models verify, we could see lower than average amounts for rainfall in California this winter, but only time will tell the story.
Have a plan in case of earthquake emergency
As the recent earthquakes in the Ridgecrest area demonstrates, be prepared for emergencies. Spend time this weekend getting your emergency plan and supply kit together. Make sure you and your family are prepared for earthquakes, natural disasters and other dangerous events. Please visit www.pge.com/beprepared for information.