Storm science

Thunderstorm anatomy

A thunderstorm is a machine of moving air. Here are every part, what each does, and how to spot them from the ground.

The updraft

The engine of every thunderstorm. Warm humid air rises rapidly, cooling as it goes. When it hits the dew point, water condenses into cloud droplets, releasing heat — feeding more rise.

Speed: 40-180 mph in strong storms.
Diameter: 1-10 km typically.
Extends from cloud base to anvil top.
In supercells, the updraft rotates — this is what makes it a supercell.
Visible as a growing tower punching through weaker clouds.

The downdraft

The engine of storm collapse. Cool, rain-cooled air descends.

Forward-flank downdraft (FFD)

Under the main rain area. Fed by evaporating raindrops. Not typically dangerous for storm-scale rotation.

Rear-flank downdraft (RFD)

Behind the updraft. Fed by evaporating precipitation. Crucial for tornadogenesis in supercells. Cutting off circulation feeds the tornado.

Microburst

Concentrated downdraft producing severe surface winds.

Wet microburst

Downdraft with heavy rain reaching ground.

Dry microburst

Downdraft with rain evaporating before ground. Very sudden wind onset.

The anvil

The flat spreading top of a mature thunderstorm.

Ice crystals blown downwind by upper-level winds.
Marks the tropopause — updraft can't rise higher.
Overshooting top: dome briefly above anvil, marks strongest updraft.
Anvil crawler lightning discharges within.
Mammatus pouches often hang from the underside.

The wall cloud

A lowered rotating cloud below the storm base — the visible mesocyclone.

Forms in the updraft region.
Rotation visible from the ground within 5-10 minutes.
Not every wall cloud produces a tornado.
Best tornado predictor is a persistent, rotating, LOWERING wall cloud.
Tail cloud may extend from wall cloud toward rain area.
Beaver tail extends into inflow region.

The RFD cut

The Rear-Flank Downdraft is invisible but crucial.

Descending air behind the updraft wraps around the mesocyclone.
It cuts through the updraft base, forming a "clear slot."
Concentrating rotation into a tighter column.
This is when a tornado descends.
Chasers look for the clear slot as the "tornado imminent" signal.

The inflow region

The area feeding the updraft.

Warm humid air flows toward the storm at 15-30 mph.
Extends 5-30 miles ahead of the visible storm.
Standing in the inflow: warm, wet, calm.
This is where chasers position for storm structure shots.
Some inflow tails can be VERY steady and photogenic.

The gust front

The leading edge of storm outflow at the surface.

Cool air surging out from the downdraft base.
Marks a sudden temperature drop, wind shift, and gustiness.
Often visible as a shelf cloud or arcus cloud.
Not the tornado — but often mistaken for one.
Can produce straight-line damage.
Outflow-dominated storms are usually past their peak.

The hail shaft

Column of hail from cloud to ground.
Distinct from rain — falls faster, sounds different.
Can be white to green tinted from ice scatter.
Green sky = high hail content aloft.
The hail zone is usually near the updraft-downdraft interface.

The overshooting top

A brief dome above the flat anvil.

Marks the strongest updraft "punching" briefly above the tropopause.
Visible on satellite as a bright spot.
Indicates most severe activity.
Persistent overshooting tops = long-lived supercell.
Damage risk peaks under and near an overshooting top.

The mammatus

Pouches hanging from the underside of the anvil.

Forms from sinking air within the anvil.
Ice crystals sublimating create localized sink.
Follows severe storms — not before.
Beautiful photograph subject.
Do not indicate danger themselves.