Unit 6 of 12 · 1 of 9 lessons published
Thunderstorms and severe weather
How thunderstorms form, how they organize into multicells, lines and supercells, and how each severe hazard develops: tornadoes, hail, damaging wind, lightning and flash floods.
The unit builds on the soundings unit. A storm's type is set largely by the instability and wind shear in its environment, and the lessons here read both from real soundings before real storms. Where a lesson describes a storm on the radar, it links to the archived scans so the feature can be seen as it was recorded.
- How thunderstorms form
Moisture, instability and lift, and the life cycle of an ordinary storm.
- Storm modes
Single cells, multicells, lines and supercells, and the wind shear that decides between them.
- Anatomy of a supercell
The updraft, the downdrafts, the wall cloud and the parts a spotter names.
- How tornadoes form
From the sounding to the vortex, and the real setups before nine tornadoes from Moore to Menasha.
- How hail forms
Updraft strength, the growth zone, and why the largest stones fall near the updraft.
- Downbursts and derechos
Microbursts, bow echoes and the long-lived windstorms they can become.
- Squall lines and QLCS tornadoes
Lines of storms, their mesovortices, and why their tornadoes are hard to warn.
- Lightning
How storms separate charge, the kinds of lightning, and the safety rules that follow.
- Flash floods
Rainfall rate, training storms and terrain, and why floods kill more people than tornadoes.
Notable individual tornadoes are documented in depth in the tornado profiles, and every tornado on record has a page in the tornado archive.