Rim Country A Hot Spot For Lightning


Two weeks ago smack dab in the middle of the Arizona Thunderstorm Safety Awareness Week U.S. Forest Service Hotshots doused six lightning-caused fires in the Tonto National Forest.

Although that sounds like a possible record-breaker, it's not not by a long shot.

"Six lightning fires in one day is not even close to the record," says U.S. Forest Service Fire Prevention Officer Gary Roberts. "Last year, when our (fire) conditions were so extreme ... this forest was averaging 10 wildfire starts a day. In this district we have five districts on the Tonto we were averaging six wildfire starts a day."

Nationally, Roberts adds, wildfires average a whopping 112,000 per year roughly half of which are caused by lightning, with the other half caused by human carelessness.

At this time of year, though, lightning produced by the summer monsoons is by far the most likely culprit not only as the cause of fires that have been spotted, but others that are'hibernating' and just waiting to spark.

"We got six fires Friday (June 22), and we know that all those are out," Roberts says. "But we're still waiting, because there could be two or three 'sleepers' out there that are smoldering and waiting to ignite. That's why we have lookouts. They stay on top of that kind of a situation."

Staying on top of that situation is a top Forest Service priority, he explains, because "We do live in an area where there's high lightning activity so much so that, if the Mogollon Rim doesn't get the most lightning in the world, it's certainly near the top of the heap.

"And even when lightning isn't starting fires, it can be very dangerous. Every year, there's probably from one to three hikers on the Rim who are killed by lightning."

According to the 1999 book "Arizona's Mogollon Rim," written by Don Dedera and published by Arizona Highways magazine, there was once a single August in which the state was hit by more than 200,000 lightning bolts, "with the greater number striking along the Rim."

According to Roberts, this phenomenon occurs because "you've got the extreme heat in the Valley, which is convection heat and goes uphill towards the Rim country. When it hits our much cooler air, when you have that contrast, it creates the type of electric field which creates lightning."

The ideal Rim country location for the creation of lightning is the area immediately surrounding the Forest Service's Diamond Point lookout tower, which Roberts says "gets more lightning discharged over it than any other tower in the district."

Tyree Wilde, a warning coordination meteorologist for the Weather Forecast Office in Flagstaff, agrees with Roberts on the dangers of Arizona thunderbolts.

"Southeast and southern Arizona get more lightning activity," Wilde says, "but the Rim gets more thunderstorms. And all thunderstorms produce lightning."

The average of lightning-related deaths in Arizona, he says, is four per year a sufficient number to earn the state a ranking of 24th in the nation within this unfortunate category. For every 10 people struck by lightning, six will survive.

In the U.S., Wilde says, lightning is Mother Nature's No. 2 killer, right behind flash floods. According to a coast-to-coast U.S. Weather Service study, an average of 86 people a year were killed by lightning between the years 1959 and 1999. It also starts more than 15,000 structure fires and burns down about 2 million acres of forest each year.

While the number of deaths for Arizona may seem low by national standards, Roberts says, nearly all of them occur during our short three-month thunderstorm season from June through August.

"At the first rumble, I ramble"

Lightning is caused when rapidly rising and descending air in a thunderstorm separates positive and negative charges. Air acts as an insulator, but when the charge builds up to a level that exceeds the air's ability to insulate the charge, the result is a spark seen as lightning. The lightning equalizes the positive and negative charged areas. Lightning can extend from one end of a cloud to another, known as in-cloud lightning. It can also extend between two clouds, which is called cloud-to-cloud lightning. Lightning which extends from a cloud to the air, while not touching the ground, is known as cloud-to-air lightning. Lightning that stretches from a cloud to the ground is known as cloud-to-ground lightning. The lightning charge heats the air about 10 times hotter than the surface of the sun and causes a shock wave that we hear as thunder.

Most lightning deaths and injuries occur during late spring and summer during the late afternoon and early evening, which is the peak time for thunderstorm development.

Unfortunately, this also is the peak season for outdoor recreation.

"I really enjoy hiking the Rim at this time of year," Roberts says. "But let me tell you, when I'm up there, at the first rumble, I ramble. I don't stick around."

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