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NATURE HAPPENINGS - August 2007

Summer Thunder Shows
by Damian Fagan

The past several days have been a tease of parading cumulus clouds - unfulfilled promises of precipitation that floated away to points east. Their presence may indicate fair weather, but, here in August, they seem to foretell the future – rain.

After a clear sunrise sky, by early afternoon there is a build-up of whipped cumulonimbus atop the La Sal Mountains. Darkened undersides indicate the possibility of rain, long overdue and ever welcomed. Today’s prediction of afternoon showers looks like a good bet and as soon as the thunder echoes off of the mountain peaks and rings in the season of summer thunderstorms, the wait is on.

Rising faster than the head of a Dead Horse Ale, these clouds achieve the stature of small eastern states, and they pack a lot more punch than a 3.2 microbrew. Derived from the Latin word kumelos meaning “a heap” or “a swelling” and nimbus meaning “violent rain,” these towering masses form aerial landscapes.

My fondness for these storms has taken a more long-distance appreciation. I’ve been caught out too many times, with bolts of fiery lightning striking all around me. I’ve sat hunched in downpours trying to make myself smaller than the shrubs around me, hoping that this day is not the day.

Though I give these thunderstorms the respect they deserve, I love this time of year. As the mercury rises, heated air masses rise and start to form pillows of white. A cloud’s base may form at 14,000 feet, but many form at lower altitudes. As this leaden air climbs, it cools and starts to condense. Minute water droplets are in constant motion within the cloud, but because of their light weight gravity has little pull on them. Air currents keep the droplets afloat until they crash into each other and coalesce into droplets greater than 1/125 of an inch. Then it’s bombs away!

In addition to the precipitation, lightning discharges within and from the clouds. Electrical charges generated within the cloud or from the ground seek out their opposites – negative to positive and vice versa. When the electrical pressure is great enough, the charges are released. A “leader” stroke may originate from the cloud, followed by a heavier return stroke from the ground. When I see the lightning, I start to count “1001, 1002, 1003,” until I hear Thor’s hammer: the tremendous heat generated creates a shock or compression wave called thunder. A 5-second difference equals about one mile. Sometimes you might feel the temperature drop as cold air flows down and out from the thunderhead. This cold air may travel ahead of the storm by several miles, allowing sufficient time to seek shelter.

Lightning strikes the Earth an estimated 30 million times a year (whose job is it to count!). Some people figure they have a better chance of winning a Powerball lottery than being struck by lightning. Unless you’re Roy Sullivan who holds the Guiness World Record for being struck 7 times in 35 years! You’d think the guy would make a better choice when dealing with 30 million volts of electricity.

Sometimes these storms break out of a precipitation slump and let lose a deluge that might last only twenty minutes, but ends up as a rumbling, gnashing flash flood barreling down a canyon.

In a land where the upper portion of the soil saturates very quickly or is impenetrable sandstone to start with, runoff tends to accumulate fast. Waterfalls appear, as if by magic, cascading over the slickrock or dry washes soon become torrents.

Not all flash floods are monsters with foaming jaws gnashing away on cottonwood trees and unfortunate livestock, but I’ve hiked in deep narrow slot canyons that have massive tree trunks wedged fifty feet above me. I’ve heard of vehicles being swept away while trying to cross a raging flood (not mine!) and I’ve experienced the Green River rising unexpectedly from a storm miles upstream, and had to suffer the consequences of an untethered boat.

Even though these August storms may be destructive, the desert usually needs the rain by August. Soaked sagebrush never smells sweeter and those flash floods may leave behind a good story. Just be aware and be safe and enjoy the show!

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