Lightning ignited a wildfire near Yarnell, Arizona on June 28, 2013 – later resulting in one of the great tragedies in wildfire fighting history. Moderate to fresh (13 to 24 mph) winds combined with 100-degree temperatures and a landscape choked by long-term drought caused the fire to burn for days across thousands of acres.
To make matters worse, most of the land around Yarnell had not burned in nearly four decades, leaving behind vast amounts of parch vegetation, which acted as fuel. Two days later, 19 members of the Granite Mountain Hotshots, an elite group of firefighters would lose their lives in a treacherous box canyon.
We may never know precisely what occurred, but a band of thunderstorms moved over their area and probably produced a microburst or strong downdraft associated. These winds can exceed 70 mph, which become powerful horizontal winds when they hit the ground. This may have caused the fire to overrun their position and take the lives of these treasured folks.
As any firefighter will tell you, three ingredients are needed to have a fire — oxygen, heat and fuel — “the fire triangle.” A heat source such as a spark from a trailer chain hitting the highway can cause a fire to ignite, but the heat also preheats the fuel in the fire’s path, allowing it to spread. The winds not only provide the oxygen for combustion but drive the fire in somewhat predictable directions. When the winds abruptly change direction or speed, the results can be deadly.
Along the Central Coast since 1931, 14 firefighters have lost their lives protecting life and property battling fires. Abrupt changes in wind velocity may have caused the death of 10 of these brave souls; most recently, the Spanish Ranch Fire took the lives four firefighters on Aug. 15, 1979.
Dan Dalits, a retired Cal Fire deputy chief, wrote me to say that all these deaths occurred between 2 and 4 p.m. between June and August when abrupt changes in the winds often happen. They also had something else in common: a strong temperature inversion layer that produced dense coastal stratus with fog and mist in the coastal regions. Dulitz referred to this atmospheric condition as “the winds with no name.”
As many Central Coast residents know, we live in a region with many microclimates, which become especially prevalent during the summer and early fall months. 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. Many times in summer, temperatures on top of the Santa Lucia Mountains never drop below 80 degrees, while along the shoreline; temperatures can be in the low 50s.
These temperature changes are often caused by the Santa Lucia (northeasterly/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 – and hazardous conditions for our firefighters.
A rule of thumb: If the marine layer is present along the coastal regions, the possibility of an abrupt wind shift is high – especially in the gaps and passes.
Another completely different facet is the fact that these giant fires can generate their own weather, producing mushroom-cloud- like formations called pyrocumulus clouds. Heat from a wildfire causes the air to rise in the atmosphere because it’s less dense, in much the same way a hot air balloon raises. As the air rises into the sky, it cools to the point that water vapor condenses to form visible clouds.
Air rising inside the cloud can trigger thunderstorms and gusty and unpredictable winds that can be life threatening. These convective storms can contain areas of organized rotation a few miles up in the atmosphere. Under the right conditions, these thunderstorms can spin out tornadoes, which occurred in April 1926 when the Tank Farm Fire in San Luis Obispo erupted.
In the years ahead, conditions will undoubtedly only get worse for our firefighters as the atmosphere continues to warm. In fact, Cal Fire predicts a 300 percent increase in wildfire risk (in terms of frequency of fire) in non-urban areas of California by 2050, compared to the 1990-2010 average. In other words, years of drought, extreme heat and 129 million dead trees have created a “new normal” for California.
In the interest of public safety, and following the wildfires in 2017, PG&E is implementing additional precautionary measures intended to reduce the risk of fires. To help meet the climate-driven challenge of increasing wildfires and extreme weather events, PG&E announced a comprehensive Community Wildfire Safety Program. To learn more, please visit www.pgecurrents.com .
One of the actions of this program is expanding the PG&E’s weather forecasting and modeling by installing a network of PG&E-owned and operated weather stations across Northern and Central California, including the Central Coast.