Jeanie
Pattern Altitude
Because the air is relatively calm and heating even with little convective turbulence so the water vapor calmly rises to where the temp/dewpoint meet, turn into clouds and just sit there like friendly little sunshades to hide beneath....
~~~~~~ or to get popped about underneath - I call them pop corn clouds because sometimes you feel like you are a kernel of pop corn in a skillet...... now if you're a glider that's just handy lift
danka