Weather Watch

A ‘perfect storm’ of fire conditions is headed for the Central Coast this week

A helicopter makes a drop on a line of flames burning above homes near Cuesta Park in San Luis Obispo on September 27, 2017.
A helicopter makes a drop on a line of flames burning above homes near Cuesta Park in San Luis Obispo on September 27, 2017. dmiddlecamp@thetribunenews.com

So far, this year’s fire season has been one of the most challenging in our state’s history for our treasured firefighters and first responders. The weather conditions along the Central Coast on Sunday through Wednesday may be some of the most challenging they’ve seen this year, and here’s why.

Last year’s rain season produced well above-average rainfall along the Central Coast. Unlike the previous years of drought, where the hills struggled to turn green in the winter and numerous trees died due to lack of water and insect infestation. This year saw vast amounts of grasses and other seasonal vegetation that turned our hills to hues of brown and gold during the summer and fall.

This abundant foliage has become the fuse to start wildfires — a volatile short fuse that wasn’t present the previous years. This Sunday into Tuesday, a large area of high pressure will build into the Great Basin, the expanse of land between the Sierra Nevada range to the west and the Rocky Mountains to the east. At the same time, a trough of low pressure will develop along the coastline.

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This condition will create gusty and dry Santa Lucia (northeasterly/offshore) winds. These winds flow from the land out to the Pacific, pushing the low coastal clouds out to sea. These Santa Lucia winds can also bring hot temperatures and bone-dry relative humidity levels. As the air mass descends the Santa Lucia Mountains, it warms at the rate of about 5.5 degrees Fahrenheit per 1,000 feet of descent.

This type of warming is the dry adiabatic lapse rate. These winds often funnel down the canyons, pulled by gravity along the Santa Lucia Mountain range. I’ve heard credible reports of these winds gusting well over 60 mph in these locations. As anyone who lives in these canyons for an extended period will tell you, just a few degrees of wind direction change can create profound changes in its velocity. In other words, if the canyon is in alignment with the incoming wind direction, speeds tend to be much higher.

Unfortunately when gusty Santa Lucia winds occur, wildfires can funnel down these canyons with incredible speed, and all these ingredients are coming together, like a perfect storm, to produce a dangerous fire threat Sunday through Wednesday.

National Weather Service meteorologist Robbie Munroe told me:

“The most critical fire weather conditions are expected Monday through Tuesday, where there will be a combination of north to northeasterly winds gusting to between 40 and 50 mph, record-breaking triple-digit heat, humidity levels lowering into the single digits, and very dry fuels. Also, very warm and dry conditions during the overnight hours in the mountains, foothills, and wind prone areas will add to this fire weather threat during this long duration of dangerous fire weather conditions. If fire ignition occurs, there will be the potential for very rapid spread of wildfire with long-range spotting and extreme fire behavior that could lead to a threat to life and property.”

Regrettably, most people don’t think about a wildfire until it’s too late. If there’s ever a time to be careful, it’s now. Here are some excellent fire prevention tips from Cal Fire:

▪ Equipment use: Use lawn mowers before 10 a.m. and never operate a mower when it’s windy or excessively dry. Use spark arrestors for all portable, gas-powered equipment including tractors, chainsaws, weed eaters and mowers. Spark arrestors are required for gas-operated equipment in wildland areas. Make sure you have enough clearance from flammable materials while grinding or welding. In wildland areas, grinding and welding operations require a permit and 10 feet of clearance.

▪ Vehicle use: Practice safe towing and make sure towing chains are not throwing sparks while driving. Make sure vehicles are properly maintained with nothing dragging on the ground. In addition to wildfire prevention, creating and maintaining defensible space can help slow or stop a wildfire. It also allows firefighters defend property. We continually monitor fuel conditions to prepare for this risk, and we work closely with public safety organizations to assist in fire response activities.

According to Cal Fire, in the future, a 300 percent increase in the risk (regarding the frequency of fire) of wildfire in nonurban areas of California is expected by 2050 compared with the 1990-2010 average due to climate change.

California already is facing the consequences of climate change, including severe drought, heat waves, stronger storms and more wildfires. To learn more about PG&E’s sustainability efforts, please visit: http://www.pgecorp.com/corp_responsibility/reports/2017/

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John Lindsey’s column is special to The Tribune. He is PG&E’s Diablo Canyon marine meteorologist and a media relations representative. Email him at pgeweather@pge.com or follow him on Twitter: @PGE_John.

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