municate short term storm details to remote locations-often the locations where balloon› ing takes place. By the very nature of the storm’s behavior, one area may be missed while another may experience high winds and a torrential downpour. This is why balloonists must keep a watchful eye for a rapidly darken› ing western or south-western sky followed by distant thunder and lightning, as well ~s local irregular shifts in wind speed and direction. Such symptoms provide approximately 30 minutes of advance warning. Dust on the horizon signals the onset of gusty surface winds of the encroaching storm determined by observing the direction of the anvil-shaped cloud blowing out ahead of the system. 

Peak gusts of a raging thunderstorm strike abruptly and leave little time for a safe landing. Even airplanes have broken up in flight several miles from a storm, so one can just imagine what could happen to a relatively frail balloon. 

A thunderstorm is said to reach maturity when rain begins to fall. Since the storm is essentially vertical the falling rain penetrates the clouds and its aerodynamic drag creates downdrafts. Each drop causes more drops to precipitate and some air is dragged downward. The result is a mass of downrushing air that turns at right angles when it reaches the sur• face and then spreads out away from the col• umn of heavy precipitation. Most of the downrushing air turns in the direction of the overall storm movement, creating a gust front that could cause a Jot of excitement for the un› wary balloon pilot. 

Even though thunderheads may be. seen to be forming in the distance, the balloonists can easily be tempted to continue flying in gentle surface winds. However, cumulonimbus clouds can affect. wind currents as far away as ten miles with abrupt changes. The balloon can actually be drawn into the storm center as warm moist air flows inward •toward the rising vertical columns of air. It is therefore highly ad› visable to never venture closer than ten miles. Instead, land and terminate all ballooning ac› tivity for the day. 

Summertime is also thermal season and it would be wise for all balloonists to respect the sun-generated weather phenomenon known as the thermal. When the lower atmosphere is heated and the lapse rate of air becomes dry› adiabatic, the conditions are ideal. 

Surfaces with low solar reflectivity and with shelter from the wind are the most likely breeding grounds. Calm conditions promote thermals by allowing more time for isolated or sheltered pockets of air to be solar-heated. Here, more heat energy is provided than the surface can absorb. The extra heat is trans• !erred to the air by convection, causing it to become buoyant. As the bubble of superheated air rises, it displaces the air above it, forcing it into an unstable condition. Under these condi• lions, as thermals form, a balloon’s drift may be abruptly shifted in speed and direction without a change in altitude or it may begin to trace a wide curved path. These are the first signs of thermal activity. Southeast-facing slopes have greater potential for thermal development than flat terrain because of the higher sun angles, thus permitting more solar heating. Thermals, like balloons, tend to drift with the wind (so one may ride along with it for a while), but break up when the wind speed exceeds 15-20 knots. 

Like in the case of the thunderstorm, a balloon can be drawn into the center of a ther• mal where the action of the vortex can cause the basket to swing outward beneath the envelope as the balloon traces a spiraling path that climbs at an alarming rate, perhaps more than 1000 fpm. This is false climb since no heat was added to the envelope by the burners. The pilot must anticipate a sudden loss of-lift and a potential downdraft when the balloon pops out of the thermal. Heat should be applied to offset a rapid uncontrolled descent. The flatt<;lning and distorting stresses on the top panel could cause an inadvertent ripout at high altitude or the side panels could split open. For this reason, the first sign of thermal activity should herald the end of ballooning for that day. 

Remember that in the summer mqnths, the sun rises earlier and heats the ground sooner. Sun angles are. high therefore the morning flight hours are reduced, especially when the air is clear, dry and calm. Fortunately, weak thermals. precede more powerful thermals. The unstable conditions during early thermal development normally warn the pilot of the pending danger, but only if he is alert to subtle changes in his balloon’s behavior. 

"Raven Owners Newsletter" 

