Stability Classification
Based on Environmental Lapse Rate (Γ = −dT/dz) in the surface layer.
Γ < 0 K/km — Absolutely Stable (Inversion). Strongest trapping.
0 to 2 K/km — Extremely Stable. Very strong trapping.
2 to 5 K/km — Very Stable. Significant trapping.
5 to 8 K/km — Moderately Stable. Some trapping.
8 to 9.8 K/km — Weakly Stable. Dispersion becoming favorable.
Γ ≥ 9.8 K/km — Neutral / Unstable. Good dispersion.
Boundary Layer
Mixing Height
Depth available for pollutant dilution.
< 500 m — Shallow. Very poor dilution, high concentrations likely.
500 – 1500 m — Moderate. Dilution is limited.
> 1500 m — Deep. Good dilution potential.
Low-Level Jet (LLJ)
Can increase surface turbulence and ventilation.
Can transport pollutants from upwind sources over long distances.
Hodograph
Mean Wind (0 – 1 km AGL)
Surface ventilation potential.
< 5 m/s — Poor ventilation. Favorable for trapping.
> 5 m/s — Good ventilation. Favorable for dispersion.
Bulk Shear (0 – 6 km)
Thunderstorm organization potential.
< 25 kt — Disorganized, single-cell storms.
25 – 40 kt — Organized multicell thunderstorms.
> 40 kt — Supercell (rotating storms) potential.
Convective Potential
CAPE (J/kg)
0 – 1000 — Marginal instability.
1000 – 2500 — Moderate instability.
> 2500 — Strong instability.
CIN (J/kg)
0 to −25 — Weak cap. Storms initiate easily.
−25 to −100 — Moderate cap. Requires strong forcing.
< −100 — Strong cap. Convection unlikely.
