Thunderstorm formation and pressure cycle
Thunderstorm needs 3 ingredients at once (remove any one: no storm):
| Ingredient | Detail |
|---|---|
| Moisture | present |
| Unstable lapse rate | or conditionally unstable |
| Lifting trigger | starts air rising: heating, front, or terrain |
- Resisting rising air kills storm: stable layer, inversion, subsidence, a high.
Lifting mechanisms (AWH 22.2):
- Surface heating
- Converging winds around a low or trough
- Front
- Upslope (orographic) flow
- Dryline
- Outflow boundary from an earlier storm
- Local circulations: sea, lake, or valley breeze
Upslope flow instead of heating: orographic thunderstorm (AWH ch.22; PHAK ch.12).
Pressure cycle near a thunderstorm:
- Approach: pressure falls rapidly.
- First gust and rain: pressure rises sharply.
- Storm passes: pressure falls back to normal.
Trap: heat or moisture alone not enough, need all three.
References
- FAA Aviation Weather Handbook (FAA-H-8083-28)
- FAA Pilot's Handbook of Aeronautical Knowledge (FAA-H-8083-25), ch.12