Lesson

WeatherXplore Thunderstorm Life Cycle

The Life Cycle of a Thunderstorm

  1. From an academic perspective, every thunderstorm has three stages.  In reality, large storms can have different parts of themselves spread over a few miles or a few hundred miles that can be at any of these three stages.  (This is discussed further in the scenario below and can be added to the lesson text).
    1. Towering Cumulus Stage – The warm moist air is rising into a tall cumulus cloud with extensive vertical development.  This phase is mostly strong updrafts (updrafts can exceed 3,000 fpm).
    2. Mature Stage – This is when rain starts falling at the surface.  At this point, you start seeing downdrafts as the cool water at the top of the cloud falls and drags adjacent air downward.  Downdrafts spread out along the surface and cause cool gusty wind to blow at the surface.
    3. Dissipating Stage – This stage is characterized mostly by strong downdrafts.  This is the stage where precipitation tapers off as the strong downdrafts cut off the supply of rising moist air and moisture is no longer carried upward. Downdrafts can be up to speeds of 6,000fpm.

The Scenario

You approach an airport to land as a precaution because there are thunderstorms that have formed along your route of flight.  You see a large cell building ahead of you as you approach the airport to land on runway 36 (there is a storm building directly south of the field approximately 10 miles away).  As you join the downwind leg you observe a steady 10-12 knot breeze right down runway 36 flowing towards the building storm.

You make your base and final turn, and as you descend through 300′ with full flaps extended you feel the airplane starting to sink more rapidly and notice your airspeed decreasing.  It is strange since you noted the windsock favoring your landing runway (runway 36) just a moment earlier, but in that short time the wind has changed direction as the thunderstorm that was located just south of the field has begun dumping rain and with it downdrafts that have hit the surface and has caused your headwind to shear to a tailwind while on final approach.

Aside from the standard wind-shear recovery techniques outlined in AC 00-54 from the FAA, you will now either be landing with a tailwind or if you use good ADM, execute a go-around and fly to another airport further away from the storm.  Remember that storms are always changing, and while part of a cell may be in the cumulus stage other parts of the storm may be changing stages and cause undesired wind shear when operating within 20nm of a thunderstorm.