The most obvious signs in looking for thermals are cumulus, yet though they may offer important information, they may tell us nothing – or they could actually mislead us. Don’t forget that clouds only tell us what is happening (or not happening) where they are. The challenge for us is to interpret them in relation to the air where we are. A pilot at 2,000 feet AGL who chases cumuli with bases at 6,000 might find a quick route down! Moreover, since clouds sometimes remain visible long after the lift that caused them is gone, one chosen randomly and without regard to genuine signs of convective action may prove to have no tactical value.
In their minimal form, cumuli may look more like wadded tissue than popcorn, yet ragged scraps no larger than your aircraft may provide crucial information. Also, generally, the smaller they are, the shorter-lived they will be, so look quickly and look often, or you may miss a vital clue and fly ‘blindly’ into miles of blue sink! If those few small wisps are the only clouds, they almost certainly mean something. And if you also find thermals where there are no clouds, then even such small cumuli probably mark the best lift available.