TORNADOES
Conditions for formation
Heat
Moisture
Conditionally unstable environment
Vertical wind shear
Wizard of OZ
Tornadoes
Local storms with violent winds that take the form of a rotating column of
Air that extends from a cumulonimbus cloud.
•Form in association with severe T-storms
•Interaction between strong updrafts
•And winds in the troposphere
MESOCYCLONE: precondition
For intense tornadoes
Tornadoes
Inflow and Outflow convergence rapidly increases
into Updraft and Wall cloud
The first observable step in
tornado formation is the slow,
horizontal rotation (a) of a large
segment of the cloud which
begins deep within the cloud
interior. The resulting large
vortices are called
mesocyclones. Under the
right conditions, strong updrafts
cause the horizontal vortex of
air to be tilted upward (b).
Tornadoes
2 Ways for formation
1. Top-down process
“dynamic pipe effect”
•Air beneath wall cloud is
Stretched by the updrafts
•Within Stretched column of
Air the flow is constricted
Leading to a tighter vortex
•Continues until tornado
touches the ground
Tornadoes
3 Ways for formation
2. Bottom-up process
Vertical wind shear
Causes a spinning effect
In the lower atmosphere
This spinning air is tilted in the vertical
As it moves under the updrafts of the storm
Near its base
Tornadoes
Formation in a non-supercell storm
•These are generally weaker tornadoes
•AKA: landspout
•Short lived
•Occur ahead of the frontal boundary
•Occur in the NE quadrant of a hurricane
•Occur over water “waterspout”
Tornadoes
STATS
Diameter: 500-2000ft
Speed: 30mph
Lifetime: 3mins. To 3 hours
Intensity: Based on the Fujita Scale (“F-Scale”)
Observed in EVERY state of the US
Top nine states: Texas
Oklahoma
Nebraska
Iowa
Illinois
Missouri
Indiana
Mississippi
Florida
The Fujita Scale
Measuring
A
Tornado
F0
gale tornado
40-72 mph
F1
moderate tornado
73-112 mph
F2
significant tornado
113-157 mph
F3
severe tornado
158-206 mph
F4
devastating tornado
207-260 mph
F5
incredible tornado
261-318 mph
Some damage to chimneys; breaks branches off
trees; pushes over shallow-rooted trees; damages
sign boards.
Lower limit is the beginning of hurricane-force winds.
Peels surface off roofs; mobile homes pushed over;
moving autos pushed off roads.
Roofs torn off frame houses; mobile homes
demolished; boxcars pushed over, large trees snapped
or uprooted; light-object missiles generated.
Severe damage. Roofs and some walls torn off wellconstructed homes; trains overturned; most trees in
forest uprooted; heavy cars lifted off the ground and
thrown.
Well-constructed homes leveled; structures with weak
foundations blown off some distance; cars thrown and
large missiles generated.
Phenomenal damage. Strong frame homes
disintegrate or lifted off foundations and carried
considerable distance; trees debarked.
Tornado Watch: possibility
Tornado Warning: Sighting