Wind shear science

How to read a hodograph

A hodograph plots the wind vector at different heights all in one graph. Once you learn to read it, you can spot a supercell environment in five seconds.

The setup

A hodograph is a polar plot. The center is calm wind. The tip of each vector represents the wind at a specific altitude — 0, 1, 3, 6, 8 km AGL, typically. Connect the dots and you get a curve.

The direction from center to the tip tells you where the wind is going. The distance tells you speed.

Two curves that matter

Straight hodograph

Winds change speed with height but not direction. Produces "splitting supercells" — left-mover and right-mover cells that separate.

Curved hodograph

Winds change direction with height. Clockwise-curved (in the Northern Hemisphere) favors right-moving supercells. Sharp low-level curl signals tornado potential.

The critical low-level curve

Zoom in on just the first kilometer of the hodograph. That is where tornado potential lives.

Straight low-level: shear present but no rotation available for the mesocyclone to stretch.
Slightly curved low-level: tornadic supercells possible.
Sharply curved low-level ("scorpion tail"): significant tornado potential. This is what meteorologists call streamwise vorticity — spin oriented along the storm-relative flow that goes straight into the updraft.

Storm-relative motion

The storm's motion vector is overlaid on the hodograph as a filled dot. Draw a line from the storm-motion dot to each altitude's wind vector — those are storm-relative winds. If the storm-relative wind at the surface is at least 30 kt, you have good tornado potential.

Hodograph size matters

A tiny hodograph means low bulk shear — probably pulse thunderstorms or multicells. A big hodograph — 60+ kt long — means strong deep-layer shear and supercell potential.

Where to see hodographs live

SPC Mesoanalysis — has a hodograph tab
Pivotal Weather — plots forecast hodographs
RAP soundings — real-time hodographs
Radiosonde launches — real observations twice daily