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.  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.  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.  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.  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.  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.  "Raven Owners Newsletter"  7 