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by John M. White |

Thunderstorms - it's That Season Again!

Thun-der-storm - n. A large dark cloud charged with electricity and producing thunder and lightning. Known to be extremely hazardous to aircraft. Year after year numerous articles are published about why pilots should avoid thunderstorms. Yet annually, 25% of all weather related aircraft accidents involve encounters with this weather phenomenon. The National Weather Service (NWS) estimates 100,000 thunderstorms develop each year in the United States! On average, 44,000 thunderstorms occur each day around the world. There are four categories of thunderstorms:
Single Cell Storms Typically last 20-30 minutes. Pulse storms can produce severe weather elements such as downbursts, hail, some heavy rainfall and occasionally weak tornadoes. All Things Aviation Blog Multicell Cluster Storms A group of cells moving as a single unit, with each cell in a different stage of the thunderstorm life cycle. Multicell storms can produce moderate size hail and weak tornadoes. Multicell Line Storms Multicell line storms consist of a line of storms with a continuous, well developed gust front at the leading edge of the line. Also known as squall lines, these storms can produce small to moderate size hail and weak tornadoes. Supercells Defined as a thunderstorm with a rotating updraft, these storms can produce strong downbursts, large hail and weak to violent tornadoes. A pilot’s inability to make a good aeronautical decision relative to flight during thunderstorm season can be disastrous! Some key points to remember:
  1. Always get an official weather briefing before every flight!
  2. Hail is one of the greatest hazards produced by thunderstorms. Because hailstones are carried upward on strong updrafts and blown downwind, hail can occur as far as 15 miles away from the storm cloud itself. This information alone should give you a good clue as to how far away, at a minimum, to fly from the thunderstorm cell(s) should you make a “go”decision.
  3. Turbulence is found in all thunderstorms. These updrafts and downdrafts are potentially destructive to any type aircraft!
  4. Lightning is caused by the discharge of electrical voltage within, or between a cloud. While the potential for injury in an aircraft by lightning is low, a lightning strike can cause severe damage to aircraft electrical equipment.
  5. Always know the direction of movement of the cell(s).
Keep in mind however, that while deviating around cells may be possible, there are no guarantees! Holes between developing thunderstorms can close in very quickly. It’s also very unlikely you’ll be able to out-climb a developing cell. For most general aviation pilots the safest option when confronted with thunderstorm activity is to stay on the ground, or find a place to land. Be sure to pick an airport that’s at least 20 miles from the storm. The further the better! That will allow for time to make a safe landing and secure the aircraft. Finally, some food- for -thought. On June 1, 2009 an Air France jet with 228 people on a flight from Brazil to Paris vanished over the Atlantic Ocean after flying into towering thunderstorms and sending an automated message that the electrical system had failed. While it will be many months, perhaps years, before the probable cause of this tragedy is known, it appears for now anyway, that violent weather may have played a factor.

About the Author

Dana D. Siewert ATP/CFI/DPE Director of Aviation Safety Anti-Drug Program Manager FAA FAAST TEAM University of North Dakota If you have any experiences you would like to share, or thoughts about t-storms, please let us know. Flying is so many parts skill, so many parts planning, so many parts maintenance, and so many parts luck. The trick is to reduce the luck by increasing the others. — David L. Baker

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