Thunderstorms can throw out intense gust fronts with winds that exceed 40 Mph so if there is a possibility of thunderstorms in your area it is best not to launch. These "gust fronts" are caused by cool air flowing out from the base of a thunderstorm, and sometimes form a long, horizontal, arc-shaped cloud just in front of the thunderstorm. The arrival of the gust front is often the best sign that a thunderstorm is arriving. Rain and lightning usually follow the gust front. If conditions are favorable for thunderstorm development, the gust front of one thunderstorm can actually act as a "cold wedge" and push up the warmer air in front of it, leading to the birth of yet another thunderhead.
It may be difficult to identify thunderstorms in unstable skies. Two common indicators are:
1. Mammatus clouds: Pouch-shaped clouds hanging down from a higher cloud layer. These pouch clouds look like dozens of gray or black half- basketballs suspended from the cloud layer above. Pouch clouds are only formed as a result of thunderstorm activity. If they're in the distance and not approaching, the thunderstorm that produced them is probably not a problem. If they're large and approaching, prepare to get hit by a storm.
2. A sudden change in the direction and strength of the wind and a sharp drop in temperature.