Thunderstorm avoidance

3 min read

Spring and summer weather offers some of the best flying opportunities for pilots; however, pilots also must have a proper understanding of all types of potential weather hazards before launching into the sky. Thunderstorms, in particular, provide a challenge to all pilots and understanding the warning signs and dangers associated with thunderstorms can be a lifesaver. 

Before pilots can learn how to avoid thunderstorms they must be aware of the weather conditions or ingredients that are most conducive to thunderstorm formation. The basic ingredients include unstable air, an initial updraft, and high moisture content. These conditions are most prevalent in the spring and summer months. Pilots must contend with thunderstorms of varying intensities in virtually all parts of the country. As a pilot, you should be aware that all thunderstorm cells progress through three distinct stages more commonly called the lifecycle of the storm that includes the cumulus, mature and dissipating stages. 

The cumulus or developing stage of a thunderstorm is marked by a cumulus cloud that is being forced upward by a rising column of air (updraft). The cumulus cloud soon looks like a tower (called towering cumulus) as the updraft continues to develop and is usually easy to identify. There is little to no rain during this stage but occasional lightning.

The mature stage is the most violent time period of the thunderstorm’s life cycle. At this point, drops of moisture, whether rain or ice, are too heavy for the cloud to support and precipitation begins falling in the form of rain or hail. This creates a downward motion of the air. Warm, rising air and cool, precipitation-induced descending air; along with potentially violent turbulence all exist within and near the cloud.

Once the vertical motion near the top of the cloud slows, the top of the cloud spreads out and takes on an anvil-like shape. At this point, the storm enters the dissipating stage. This is when the downdrafts spread out and replace the updrafts needed to sustain the storm. It is important to understand that all thunderstorms are dangerous to all aircraft no matter the stage they display. 

While we may long for the capability of jet aircraft in topping some thunderstorms, it is impossible to fly over thunderstorms in light aircraft. Severe thunderstorms can punch through the tropopause and reach staggering heights of 50,000 to 60,000 feet depending on latitude. Flying under thunderstorms can subject aircraft to rain, hail, damaging lightning, and violent turbulence. The clear answer is to stay completely away from thunderstorms. 

So how do we avoid thunderstorms while we are flying? A good rule of thumb is to never fly closer than five miles to any visible storm cloud with overhanging areas and strongly consider increasing that distance to 20 miles or more if possible. It’s possible to encounter hail and violent turbulence anywhere within 20 miles of very strong thunderstorms. If you see weather conditions that display signs of a developing thunderstorm, the best course of action is to turn to the nearest airport and wait for the conditions to subside.

In the situation that you find yourself caught in a thunderstorm, there are actions that you must take immediately to affect the best possible outcome. First, at the first sign of turbulence, reduce airspeed immediately to the manufacturer’s recommended airspeed for turbulent air penetration for a specific gross weight (that is, maneuvering speed, or Va). If the aircraft inadvertently penetrates the thunderstorm, do your best to maintain a straight and level attitude on a heading that will take you through the storm area in the minimum time. If time and conditions permit, seek the assistance of ATC in plotting an escape route and don’t hesitate to declare an emergency.

Never let compulsion take the place of good judgment. By understanding basic weather theories, a pilot can make sound decisions during flight planning after receiving weather briefings. With a proper weather briefing before departing, pilots can avoid days and situations that are conducive to thunderstorms. Taking proper steps and having an understanding of this type of weather could save your life.

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