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Thunderstorms are fueled by moisture. As water vapor condenses it releases latent heat and this heat is used to fuel further vertical development. In order for the water to condense the air it is contained in must first be lifted to an altitude at which it will cool to its dewpoint. This lifting can come in many forms, it can be orographic, convective, or frontal. No matter how it happens, the important thing to know is that the air is being lifted to where it reaches its dewpoint. This brings us to the third element needed to form a thunderstorm. If the air being lifted is stable it will resist being lifted further and shut the whole process down. However if it is unstable it will continue to rise until it runs out of moisture, consequently unstable air usually has a high moisture content with which to fuel vertical development.

There are three stages to a thunderstorm cumulus, mature and dissipating.

In the cumulus stage vertical movement of the air is initiated and the cloud begins to grow if sufficient moisture is present. Eventually the cumulus cloud grows into a towering cumulus cloud. During this stage water vapor condenses into small water droplets but does not fall because of the rising air.

As the water droplets become too large to be supported by the updrafts they begin to fall and cause a downdraft to be formed in the cloud. This signals the mature stage of the thunderstorm. The picture to the left shows the up and downdrafts present in a mature thunderstorm.

The dissipating stage of the storm begins as the downdrafts begin to spread out in the cell and replace the weakning updrafts. As this occurs the vertical development of the storm begins to stop and the release of latent heat is also stopped. Because of this, the storm begins to diminish in size and strength and the once strong updrafts are no longer present. They have now been replaced by downdrafts and the once great cloud begins to fall from the sky in the form of high wind.

There are two major classifications of thunderstorms, airmass and severe thunderstorms. Airmass thunderstorms tend to be of a lesser intensity than Sever thunderstorms. The difference comes in how they are formed. Airmass thunderstorms are formed in an area of moist unstable air. This moist airmass is lifted by convection on warm summer days or in some cases mountain peaks. Airmass thunderstorms tend to be widely scattered and of shorter duration than severe thunderstorms.

Severe thunderstorms are usually associated with fronts, converging winds, or troughs. Because of the greater energy available for lifting, these storms grow to enormous size. The duration of severe thunderstorms can be less than an hour for single cell storms or more than 2 hours for supercell storms. Severe thunderstorms usually contain winds greater than 50 knots and hail greater than 3/4 of an inch in diameter.

Obviously, thunderstorm avoidance is crucial for your continued existance as a pilot. The best rule of thumb for flying when thunderstorms are in the area is not to. Thunderstorms are often embedded in large layers of clouds making them very hard to see. If you find yourself in the same piece of sky as a thunderstorm due to a bad weather briefing, give the thunderstorm plenty of respect by staying at least 20 miles away. Often wind, turbulance, and giant hail stones, are encountered within 20 miles of a storm. If you end up inside of a Thunderstorm good luck!! About all you can do is set your power and trim to maintain an airspeed below Va, hold the wings level and accept variations in altitude. Hold your course because this should get you out the other side in the shortest time.