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closeLarge wildfires can create their own weather. As summer comes to an end and fall begins on Tuesday, we enter into a difficult time for our firefighters.
Historically, the fall season can bring some of the warmest temperatures and driest conditions of the year to the Central Coast.
For a fire to develop and flourish, you need three ingredients: oxygen, heat and fuel. This is referred to as the fire triangle.
Weather conditions can directly affect the fire triangle: First, warmer air encourages potential fuels — sticks, underbrush and trees — to ignite and burn faster.
Secondly, winds further dry the potential fuel and supply fires with additional oxygen.
Winds such as the Santa Anas, which blow from the land to the ocean in Southern California, can produce very hot temperatures and low relative humidity levels. These and other winds can spur a fire to move faster and engulf more land.
To make matters even worse, large wildfires are often capable of modifying local weather conditions to the point of creating their own weather.
The large smoke clouds emanating from these fires are known as a pyrocumulus and, much like a common cumulonimbus cloud, can produce strong updrafts and downdrafts.
The winds can make life for the pilots who drop fire retardant in the path of these fires from aircraft, and for firefighters on the ground, extremely difficult and hazardous.
These fire-generated winds can cause wildfires to charge rapidly up mountainsides and even downhill. The smoke from these fires can actually be seen from weather satellites.
These violent fires can generate cyclones, called fire whirls. Fire whirls, which resemble tornadoes, result from the vortices created by the fire’s heat.
They can be deadly, as seen on April 7, 1926, when a Pacific storm came in from the west and produced lightning in San Luis Obispo County.
The lightning struck large oil tanks along Tank Farm Road. Altogether, more than 5 million gallons of oil burned over five days.
Burning oil reportedly made it all the way to Avila Beach by way of San Luis Obispo Creek. The intense heat from these fires produced hundreds of fire whirls, many of which showed characteristics of true tornadoes.
One of the fire tornados traveled 1,000 yards, picked up a house and carried it 150 feet, killing the two occupants inside.
We all must take precautions to limit the number of fires.
Fire prevention and protection information can be found at www.fire.ca.gov.
This week’s forecast
Today’s low clouds, fog and areas of drizzle will burn off later this morning from the coastal valleys, but will persist along our most of our northwesterly facing beaches (Los Osos) for most of the day.
The exception will be our southerly facing (Avila Beach) beaches which will see the sun by this afternoon.
Today’s high temperatures will range from the low to high 90s in the interior.
The coastal valleys will mostly be in the 80s while our beaches will range from the mid 60s to low 70s, except for Avila Beach which may reach the low 80s.
Marine low clouds will redevelop along our coastline tonight, but will not be nearly as extensive as this morning’s.
As summer comes to an end, Monday will mark the beginning of a warming trend across California as an area of strong high pressure builds over the Great Basin.
This condition will produce northeasterly (offshore) winds during night and morning hours and mostly clear, dry and much warmer weather.
The first days of fall, Tuesday through Wednesday look to be the warmest of the week as the gentle to moderate (8-18 mph) afternoon northwesterly (onshore) winds will only cool the immediate coast within one or two miles of the beaches each afternoon.
Temperatures readings will range from the high 70 to mid 80s at the beaches, the mid to upper 90s across the coastal valleys, and the low 100s in the interior. San Francisco is forecast to reach the high 90s during this period.
Increasing northwesterly (onshore) winds combined with the return of the marine layer will contribute to much cooler temperatures Thursday through Saturday.
Surf report
The wind fields have shifted northward and have left behind a 4- to 5-foot northwesterly (305-degree deep-water) swell (with a 7- to 12-second period) this morning.
This northwesterly swell will continue at this height and period through Monday, decreasing to 3 to 4 feet on Tuesday through Wednesday morning.
A 2- to 4-foot northwesterly (305-degree deep-water) sea and swell (with a 4- to 11-second period) is forecast along our coastline on Tuesday afternoon through Thursday.
Typhoon Choi-Wan about 600 miles west of Japan will move rapidly northeastward and become extratropical.
If the charts prove to be correct, a low height, but very long-period northwesterly swell should arrive along our coastline on Friday.
Arriving from the southern hemisphere:
A 1- to 2-foot southern hemisphere (195-degree deep-water) swell (with a 15- to 17-second period) will arrive along our coastline today.
This swell will increase to 2 to 3 feet (with a 14- to 16-second period) on Monday and will continue at this height and period through Thursday.
Conservation tip
Power strips block standby power for the peripheral appliances around your TV or computer.
To learn more, visit www.wecandothis.com.
John Lindsey is a communications representative and meteorologist for Pacific Gas and Electric Co. inSan Luis Obispo. E-mail him at pgeweather@pge.com.
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