Atmospheric stability

Stability describes whether the atmosphere dampens (stable), continues (unstable), or is neutral to vertical motion.

Source: AMS Glossary of Meteorology; WMO; FAA-H-8083-25B PHAK.

Stable layering

Stable atmospheric layering prevails when induced vertical air movement is immediately dampened, causing the air parcel to return to its original layer due to restoring buoyancy forces, preventing continued ascent or oscillations.

Symptoms: stratiform clouds (stratocumulus, altostratus), haze, surface inversion, fog.
Typical in highs and at frontal inversions.

Unstable layering

Unstable atmospheric layering occurs when ascending air parcels remain warmer and less dense than their surroundings despite adiabatic cooling, promoting continued vertical motion and potential convection.

"Unstable atmospheric layering" prevails when a vertical movement of air, once induced, continues and the air cannot return to its original layer.

Symptoms: cumulus, showers, thunderstorms, turbulence.
Typical at cold-front backsides, hot summer days, maritime-tropical air.

Neutral layering

ELR = DALR (for dry) or ELR = SALR (for saturated).
Rising air has no preferred direction.

Comparison

Vertical profile	Stability	Visible in
ELR < SALR	absolutely stable	inversion, fog, stratus
SALR < ELR < DALR	conditionally unstable (saturated)	varies with parcel
ELR > DALR	absolutely unstable	cumulus, Cb, showers, turbulence

Thermal lift

Thermal lift can only occur in unstable atmospheric conditions:

Sun-heated ground creates warm air bubbles (thermals).
These rise in the unstable layer to condensation height → cumulus.

Subsidence and stabilisation

"Air gradually stabilises by subsidence" means wide-spread subsidence of an air mass can cause a subsidence inversion which blocks vertical development of clouds:

In highs, air sinks from altitude.
This air warms adiabatically → warm layer over cool surface air → inversion.
Consequence: stable atmosphere, little cloud development above.