The Fujita-Pearson scale, more commonly known simply
as the Fujita Scale, was devised by eminent meteorologists
Tetsuya Theodore Fujita and Allen Pearson. It provides
a scale against which to measure intensity and damage of
tornados. It also used to include classifications based
on the width and length of a tornado's damage path, but
later meteorological research raised
serious questions as to the validity of the path metric and it
has been dropped from most uses.
Although the scale is expressed in terms of wind speeds it is
actually a measurement of the amount of damage done by a tornado.
An extremely strong tornado, even one with F5 force winds, will
still be classified as an F0 or an F1 if it occurs in a large open
field with no buildings or trees. This also makes it difficult to
distinguish between the stronger levels of the scale when the tornado
is in a densely populated area. It can be difficult to tell whether
damage was directly caused by wind or if it is a secondary
effect such as an airborne vehicle striking something.
F0, 40-72 mph, Path .3-.9 miles long, 6-17 yards wide
At 40 mph the wind makes it walking difficult for an adult and impossible
for a child, signs break and branches blow off of trees. At 50 driving a
compact car is risky, especially in open areas, and large branches snap
like small twigs. At 60 driving a high profile vehicle is
suicidal while chimneys start to take damage from branches flying through
the air like biological shrapnel. At 70 you've made it to hurricane
force--shallow-rooted trees in soft soil uproot, driving isn't possible,
neither is walking.
F1, 73-112 mph, Path 1-3 miles long, 18-55 yards wide
From 70 to 110 mph the winds rip shingles from roofs, projectiles
present a serious danger to anyone caught outside. Mobile homes,
damned by the combination of a weak foundation and a wide wind-catching
profile, turn over. Someone caught on the road will have their
vehicle thrown violently by the wind, the faster they're moving
the more likely their vehicle will take flight.
74% of all tornados are F0 or F1 in intensity. 4% of all tornado deaths
are in F0 or F1 storms.
F2, 113-157 mph, Path 3-10 miles long, 50-175 yards wide
Mobile homes are toast. Frame houses lose their roofs, ripped completely
off by the winds of an F2 tornado. Even large trees begin to come up out
of the ground, though they merely fall back to it after doing so. Trains
derail, the cars flipped over by the winds. Large branches and debris from
damaged building pose significant threats.
F3, 158-206 mph, Path 10-30 miles long, 150-600 yards wide
At this level tornados become truly terrifying. Not just the boxcars,
but the engines of trains are thrown about. Older homes or homes not
securely anchored to their foundations can become airborne. Whole trees
are thrown tremendous distances at very high speeds and large stands of trees
are completely uprooted.
25% of all tornados are F2 or F3. 29% of all tornado deaths are caused
by these storms.
F4, 207-260 mph, Path 30-100 miles long, .3-1 miles wide
Well-constructed houses are utterly destroyed, turned into missiles.
Enormous trees are picked up and thrown about, whole forests treated
like the toothpicks in Rain Man. Cars reach speeds their designers
never intended--the only time you'll see an AMC Gremlin go 250 is
when it's pushed by an F4 tornado.
F5, 261-318 mph, Path 100-300 miles long, 1-3 miles wide
The most devastating class of storm. Large, steel-reinforced concrete
structures take significant damage, mostly from small, steel-reinforced
concrete structures that have turned into a wall of total devastation
travelling at half the speed of sound. Trees that aren't uprooted
have all of their bark stripped off, cars can be thrown upwards of 300
to 400 feet, and pretty Kansas girls flit off over the rainbow.
1% of all tornados are F4 or F5 in intensity but they are responsible
for 67% of all tornado deaths.