Environmental Lapse Rate (ELR)
ELR is the Temp change with height that is recorded by a weather balloon
ELR is absolutely unstable in a thin layer just above the ground on hot, sunny days
Ahrens,
Meteorology Today 5th Ed.
ELR is 6.5o C/km, on average, and thus is conditionally unstable!
6.0o C/km
10.0o C/km
6.5o C/km