Aero-Tips!

A good pilot is always learning -- how many times have you heard this old standard throughout your flying career? There is no truer statement in all of flying (well, with the possible exception of "there are no old, bold pilots.")

Aero-News has called upon the expertise of Thomas P. Turner, master CFI and all-around-good-guy, to bring our readers -- and us -- daily tips to improve our skills as aviators. Some of them, you may have heard before... but for each of us, there will also be something we might never have considered before, or something that didn't "stick" the way it should have the first time we memorized it for the practical test.

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Aero-Tips 08.13.06

We hear about them a lot out here in Kansas... but for many "bow echo" is a new term.  Here's why you need to know the implications of this phenomenon.

A bow echo is a radar return shaped like an archery bow. It is a visual representation of an extreme gust of wind, usually the outflow from a severe thunderstorm. Bow echos often result from a line of convective cells associated with damaging straight-line winds and small tornadoes. Bow echoes include an intense inflow of wind at the core of the bow, with book-end or line-end vortices behind the ends of the bow.

Bow echoes have been observed with scales between 20 and 200 kilometers, with lifetimes from three and six hours. At early stages in their evolution, both cyclonic and anticyclonic book-end vortices tend to be of similar strength, but later in the evolution, the northern cyclonic vortex often dominates, giving the convective system a comma-shaped appearance.

Salt Lake scenario

A bow echo event in and near Salt Lake City, Utah on August 1, 2006, was so intense that the National Weather Service (NWS) has posted a web page specifically describing the scenario and its aftermath. Two bow echoes impacted the Wasatch Front. Both bow echoes produced damaging straight-line winds near the apex of the bow segment, characteristic of this type of severe thunderstorm. Peak wind gusts were measured at 92 mph at the Provo Airport and estimated between 60 and 70 mph in East Millcreek of Salt Lake County. Rainfall was very intense with these thunderstorms as many areas in the southern Wasatch Front observed one half to one inch in less than 30 minutes. Hail stones as large as ¾ of an inch in diameter were observed with the thunderstorms in Provo. Preliminary damage estimates in Utah County were around $13 million.

The NWS site even has a recorded radar loop of the Salt Lake event. Yellow boxes in the loop are Severe Thunderstorm Warnings issued by the National Weather Service.

Why it's important for pilots

Hail accumulated on the Provo Airport runways and was still present in piles during the evening hours. There was also considerable damage to small airplanes which were toppled over by the wind, and to buildings which had roofs and siding partially or totally torn away at the Provo Airport.

Aero-tip of the day: See a bow echo on radar? Avoid the extreme turbulence, and expect its effects to last long after the storm passes. You may have to divert elsewhere even after the skies clear. If you see a bow echo while your plane is on the ground, get it inside if possible... and hope the hangar holds together.

FMI: Aero-Tips