Warm moist air from below meets cold dry air from above.
Wind shift (change in speed and direction with height) twists the airflow into a horizontal vortex.
Exiting cloud streams lift and tilt this vortex vertically, pulling
the whirl downward — thus forming a funnel tornado.
Fujita scale (EF)
EF0 — up to 137 km/h, light roof damage.
EF1 — 138–178 km/h, roofs are stripped, vehicles are overturned.
EF2 — 179–218 km/h, destroys building roofs.
EF3 — 219–266 km/h, demolishes walls, overturns trains.
EF4 — 267–322 km/h, tears buildings off their foundations.
EF5 — over 322 km/h, total destruction, downpour.