Physical Geography 101


Rapidly rotating winds around a small area of intense low pressure.
Commonly as twisters or cyclones.

Basic Stats

Diameter - 100 to 600 m average (300-2000 ft)
can range from a few meters to 1600 m (1 mile)
Movement - SW to NE
>Ground Speed - 35-75 kph average (20-40 knots) (23-46 mph)
Duration - few minutes to hours
Path Length - 7 km average (4 miles)
Rotation - counterclockwise and clockwise (rare) in the Northern Hemisphere

Enhanced Fujita Scale

This is a scale based on wind speeds used to categorize tornados

Scale Speed mph Speed kph
EF0  65-85 mph 105-137 kph
EF1 86–110 mph 138–178 kph
EF2 111–135 mph 179–218 kph
EF3 136–165 mph 219–266 kph
EF4 166–200 mph 267–322 kph
EF5 >200 >322 kph

Stages of Tornado Development

1) Dust-Whirl Stage - swirling dust marks tornado circulation
2) Organizing Stage - tornado increases strength/intensity; funnel cloud extends downward
3) Mature Stage - damage is most severe; funnel diameter is at its maximum; funnel is nearly vertical
4) Shrinking Stage - decrease in funnel diameter; increased funnel tilt; narrowing of damage swath at surface
5) Decay Stage - funnel becomes rope-like, contorted, dissipates

Tornado Formation

Formation along Polar Front

Formation along Dry Line

Tornado Alley

Unique Conditions:

Outline for the video Tornado!.

This video will be shown during classtime. The outline provided below is simply a list of the major topics covered in the video and is not intended to be a substitute for viewing the video. The entire video may also be viewed on YouTube at the following link: NOVA: Tornado!.

I. Tornado Alley
II. Tornado Characteristics and Formation
III. Tornado Chasing
IV. Tornado Experiments
V. Barneveld, Wisconsin