The months of June and July saw slightly below to average seasonal temperatures throughout the Central Coast, along with much of California.
Other parts of the world haven’t been so fortunate; in fact, the global average temperature this past July was the hottest month ever recorded. These record-breaking July temperatures contributed to record wildfires in Alaska and Siberia.
Earlier this summer, 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 generally occurs during the summer. That, in turn, allowed a deeper marine layer to develop, producing milder temperatures.
This August was slightly warmer than typical in most Central Coast locations. Paso Robles Airport averaged 95 degrees or about 2 degrees above normal. San Luis Obispo usually sees a high of 79 degrees in August, but this year saw an average high of 80 degrees. Santa Maria Airport reported an average high of 76 degrees, or about 3 degrees above normal.
After I reviewed the PG&E Diablo Canyon weather forecast from past years, this August saw a more considerable amount coastal stratus “Fogust” with more fog, mist and drizzle than in 2017 and 2018. So many people I’ve spoken with this month have commented that this summer is how they remember Morro Bay and Los Osos in years past with their long stretches of overcast skies.
This last rainfall season (July 1, 2018, through June 30, 2019) produced above-average rainfall and snow throughout much of California. Locally, SLOWearther.com in western San Luis Obispo finished with 32 inches or 132 percent of typical. The rain gauge at Diablo Canyon saw 20 inches or 107 percent of normal. Cal Poly reported 25 inches while Paso Robles, Santa Maria, and Santa Ynez recorded 14 inches and Lompoc 16 inches.
This above-normal rainfall combined with near historical seasonal temperatures has kept the moisture content of vegetation/fuels above normal. The higher the moisture content, the more difficult it is to burn. Locally, according to Cal Fire San Luis Obispo County and Santa Barbara County Fire Department, live fuel moisture levels are above average this year, unlike last year when they were well below.
So far this year, these favorable conditions have resulted in one the quietest starts to the California wildfire seasons since 1998. You may remember, 1998 was very strong El Niño year. Diablo Canyon recorded 44 inches of rain; the month May of 1998 saw nearly 5 inches at Cal Poly.
Regrettably, it’s no time to be complacent. The Climate Prediction Center is advertising that warmer than typical conditions with below-normal precipitation will continue through November, if not longer, so wildfire conditions could change rapidly.
In September, October and November, high-pressure systems often move over the Great Basin — the space between the Sierra Nevada range to the west and the Rocky Mountains to the east. This condition can produce strong to gale-force northeasterly down-slope winds. These down-slope winds are technically called katabatic wind, from the Greek word katabatikos, which means “going downhill.”
As the air mass descends the side of the mountain range, 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. 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, creating potentially horrific fire conditions.
As part of its efforts to prepare customers and communities for the growing threat of wildfire, PG&E has launched a robust weather webpage (www.pge.com/weather). This page offers a seven-day, look-ahead regional forecast updated daily by a PG&E meteorologist or fire scientist that indicates the potential need to call a Public Safety Power Shutoff (PSPS).
No single factor drives a Public Safety Power Shutoff, as each situation is unique. PG&E carefully reviews a combination of many criteria when determining if power should be turned off for safety. These factors generally include, but are not limited to:
▪ A Red Flag Warning declared by the National Weather Service (Note: A Red Flag Warning alone does not automatically trigger a PSPS).
▪ Fire Potential Outlooks from the Interagency Geographic Area Coordination Centers.
▪ Low humidity levels, generally 20 percent and below.
▪ Forecasted sustained winds generally above 25 mph and wind gusts in excess of approximately 45 mph, depending on location and site-specific conditions such as temperature, terrain and local climate.
▪ Condition of dry fuel on the ground and live vegetation (moisture content).
▪ On-the-ground, real-time observations from PG&E’s Wildfire Safety Operations Center and observations from PG&E field crews.
Beyond PSPS information, weather enthusiast will find a lot to like about the new weather page.
With PG&E’s weather map at your fingertips, you’ll be able to check humidity, precipitation, temperatures, wind speeds and wind gusts across 70,000 square miles of Northern and Central California.
You can also check out those same conditions in your hometown, based on the closest weather station. Additionally, the map shows whether the National Weather Service has called a Red Flag Warning and where. It also offers access to the thousands of weather stations and dozens of high-definition cameras in use by PG&E.
I will be giving a presentation about climate change, and what it means for our local weather at ECOSLO’s Green Drinks event on Tuesday, Sept. 10, from 5:30 to 7 p.m. at 7 Sisters Brewing Co., 181 Tank Farm Road in San Luis Obispo. All are welcome, including families.