Supercell

Most thunderstorms are crowds: clusters of short-lived cells, each living under an hour. A supercell is a soloist — one single, huge storm built around a rotating updraft (called a mesocyclone), able to live for many hours and travel hundreds of kilometres.

>What makes it special

The rotation changes everything. A spinning, tilted updraft is aerodynamically tidy: it separates its intake (warm inflow at the base) from its exhaust (rain and cold air downwind), so it never chokes on its own precipitation like ordinary storms do. That one trick lets a supercell:

• outlive everything else — hours instead of minutes;
• grow giant hail — hailstones ride the rotating updraft in loops, collecting layer after layer of ice before they're heavy enough to fall;
• spawn strong tornadoes — nearly all violent tornadoes come from supercells, born where the mesocyclone tightens toward the ground.

>Spotting one

On radar, a mature supercell often shows a hook echo — a comma-shaped curl of rain wrapping around the rain-free rotating core. In person, the tell is a striated, barrel-shaped cloud base that visibly turns, often with a lowered wall cloud beneath it.

The recipe is exactly the outlook's ladder: fuel (CAPE) plus a strong deep- shear engine gets you supercells; add low-level spin and a low cloud base and you're in tornado territory. That's why "ORGANIZED STORMS" is the outlook's second-highest rung — the supercell level.