THUNDERSTORMS &
TORNADOES
QUESTION OF THE DAY
Where
would you expect to
find the greatest proportion
of Tstorms and why?
CYCLONE
Circulation
around ANY lowpressure center
 Intensity and size do not
matter
 Tornadoes and Hurricanes are
smaller than mid-latitude
cyclones and more violent
THUNDERSTORMS
Storm that produces lightning and thunder
 Characterized based upon the up/down draft of
air NOT circular motion of air
 Forms when warm, humid air rises in an
unstable environment
 Unequal heating of earth’s surface (Air-Mass
Tstorms)
 Unequal heating along with frontal wedging or
oorgraphic lift (Severe Tstorms)

AIR-MASS THUNDERSTORMS

Occur in mT air that moves Northward from
Gulf.
Most frequent during Spring and Summer
 Frequently around midafternoon


Thunderstorm Project produced a model of the
life cycle of a Tstorm
Cumuls Stage
 Mature Stage
 Dissipating Stage

CUMULUS STAGE
 Formation
of cumulus clouds allow for
moisture to be at greater heights
 Clouds grow vertically
 Cumulonimbus clouds form
 Dominated by updraft
 Downdraft forms and failing precipitation
causes drag
 Entrainment intensifies downdraft
MATURE STAGE
Officially starts when precipitation leaves the
cloud
 Updraft and downdraft exists side by side and
grow the cloud

Anvil top forms when cloud reaches base of the
stratosphere
 Most active stage: Gusty winds, ligthning, hail/heavy
precipitation

DISSIPATING STAGE
Dominated
by the
downdraft
Cooler air aloft and falling
precipitation causes cloud
to evaporate
SEVERE THUNDERSTORMS

Characterized by heavy downpours, flash
flooding, strong/gusty winds, hail, lightning, and
maybe tornadoes.
 Must have winds over 58mph or hailstones .75
in diameter or produce a tornado
SUPERCELL TSTORMS

Single, powerful cell up to 65,000’ and 12-30
miles in diameter


2000-3000/year in the US
Can form mesocyclones when updraft rotates
THUNDER & LIGHTNING

Thunder is: Expanding air

Heat Lightning
Lightning is created due to separation of charges
in a cumulonimbus cloud
 Sheet Lightning

Within the cloud or between clouds
 80% of all lightning


Cloud to Ground Lightning
20% of lightning strokes
 Most damaging and dangerous


Flash is made up of individual strokes
 Leader, step leader, return stroke, and dart leader
TORNADOES
AKA: twisters, cyclones
 Violent windstorms that are a vortex
 Contains lower pressure inside the vortex than
the surrounding areas

TORNADO FORMATION

Form in association with severe thunderstorms
Located wherever severe weather is: cold fronts,
squall lines, hurricanes, supercells
 Only tornado if funnel cloud touches surface

F-SCALE

Fujita Intensity Scale

Determined based upon damage produced
TORNADO FORECASTING
Watches

Alters public to
POSSIBLITY of
tornadoes over a
specific area for a
certain time period.

65,000sq.km for 4-6
hours
Warnings
Issued by local NWS
 ACTUAL sighted
tornado in an area or
indicated by radar


Smaller areas and for
shorter periods of time