Nature does great special effects
Published: Sunday, Sep. 18, 2011
Flashes of light in the eastern sky and the distant rumble of thunder, followed by hail and rain showers, may have been your wake up call the morning of Sept. 10.
As the day progressed, potent cumulonimbus clouds with the slate gray bases and tall billowing towers moved westward over San Luis Obispo. The air turned electric and fashioned one of the most intense displays of lightning that I have ever seen.
According to the lightning tracker at SLOweather.com, about 30,000 lightning strikes were recorded within a 50-mile radius of San Luis Obispo on that Saturday. By that evening, lightning strikes reached more than 100 per minute. These lightning strikes kept Cal Fire and other fire departments throughout Central California extremely busy extinguishing vegetation fires.
These thunderstorms were caused by an upper-level low pressure system that moved over the Central Coast and pulled in warm and humid monsoon moisture from the south. The warm and moist air rose rapidly into the sky.
As the air rises, it condenses and forms cumulus clouds that can tower over the earth. This condensation process releases latent heat and, like turning on the burner in a hot-air balloon, it warms the surrounding air, which continues to rise at surprisingly high speeds. At times, it can reach more than 40,000 feet in altitude and actually break into the stratosphere.
Last year, a hailstone weighing nearly 2 pounds plummeted to Earth from a thunderstorm in South Dakota. This monster piece of ice was found by ranch hand Leslie "Les" Scott near a small town of about 100 people named Vivian, on the high plains. The hailstone probably took violent updrafts that exceeded 160 mph to remain suspended in the cloud over the course of five to 10 minutes!
The updrafts and downdrafts found in thunderstorms can create friction between rapidly moving ice particles and rain traveling in opposite directions.
This wipes off electrical charges, which generate an increase in electrical pressure or voltage. The same effect can sometimes be experienced by rubbing your shoes across a wool carpet on a dry day and then touching a door knob. The shock you feel is the electricity discharged to the doorknob.
When electrical pressure or voltage becomes high enough, charges between parts of the cloud or between the cloud and the ground are released as lightning. Lightning occurs at all levels in a thunderstorm. The majority of lightning strikes never hit the ground.
When lightning does hit the ground, it starts with a relatively thin "leader" stroke from the cloud, followed immediately by a heavy return stroke from the ground.
Lightning discharges are incredibly powerful — up to 30 million volts at 100,000 amps. Just one bolt is more than six times hotter than the surface of the sun. But they last only briefly. The sudden and rapid increase in heat causes the air around the lightning bolt to rapidly expand, then collapse, causing the shock waves that we call thunder.
Lightning takes the path of least resistance. It tends to hit the highest places. Never stand under a lone tree in an open field or on top of a mountain during thunderstorms. If you're backpacking in the mountains and you feel your hair standing on end, get as low to the ground as you can and try to take cover.
On buildings, lightning rods allow electrons to stream off into the air or harmlessly to the ground. Wood structures and trees have high electrical resistance and can be heavily damaged unless grounded.
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