A single storm cell is driven by parcel theory: undiluted maximum updraft speed scales with the square root of Convective Available Potential Energy, w_max ≈ k·√(2·CAPE) (an entrainment efficiency k≈0.5 is applied, since real updrafts reach only about half the idealized value). Higher instability shortens the time needed to build a towering cumulus, and higher humidity feeds more condensate into the cloud, raising the rainfall rate once precipitation starts.
w_max = 0.5 · √(2 · CAPE)
growth time ∝ 1 / CAPE
rain rate ∝ humidity · updraft fraction
mature hold ∝ wind shear
Wind shear separates the updraft and downdraft so falling rain no longer chokes off the inflow — the classic reason sheared storms organize and live far longer than unsheared single cells. Here it stretches the mature stage and tilts the cloud and rain shaft downwind, the same tilt that lets real supercells sustain themselves for hours. Lightning strikes fire stochastically at a rate proportional to updraft strength and moisture (a proxy for the graupel–ice collisions that separate charge in the mixed-phase region), peaking in the mature stage.
- Cumulus stage — pure updraft, cloud builds, no precipitation yet.
- Mature stage — updraft and downdraft coexist, heaviest rain and most lightning.
- Dissipating stage — downdraft and rain-cooled outflow spread at the surface (the gust front) and cut off the inflow, the cell weakens and a new one can form.