Page 39 - CCPS Monograph - Natural Hazards

Scale Wind Estimate Typical Damage
kph(mph)
F4 333.1-418.8 Devastating damage. Well-constructed houses leveled; structures
(207-260) with weak foundations blown away some distance; cars thrown
and large missiles generated.
F5 Incredible damage. Strong frame houses leveled off foundations
420.0-511.8 and swept away; automobile-sized missiles fly through the air in
((261-318) excess of 100 meters (109 yds); trees debarked; incredible
phenomena will occur.

An update to the original F-scale by a team of meteorologists and wind engineers, implemented in the
U.S. on 1 February 2007. The Enhanced F-scale still is a set of wind estimates (not measurements)
based on damage. Its uses three-second gusts estimated at the point of damage based on a judgment
of 8 levels of damage to the 28 indicators listed below. These estimates vary with height and
exposure. Important: The 3-second gust is not the same wind as in standard surface observations.
Standard measurements are taken by weather stations in open exposures, using a directly measured,
"one-minute mile" speed. (SPC 2019)

Table G.3 Enhanced Fujita Tornado Damage Scale (adapted from SPC 2019)

Fujita Scale Derived EF Scale Operational EF Scale
F Fastest 3 Second EF 3 Second EF 3 Second
Number 1/4-mile Gust kph Number Gust kph Number Gust kph
kph (mph) (mph) (mph) (mph)
0 64-115 72-126 0 104-137 0 104-137
(40-72) (45-78) (65-85) (65-85)
1 117-180 127-188 1 138-175 1 138-177
(73-112) (79-117) (86-109) (86-110)
2 181-253 189-259 2 177-220 2 178-217
(113-157) (118-161) (110-137) (111-135)
3 254-333 260-336 3 222-268 3 218-265
(158-207) (162-209) (138-167) (136-165)
4 334-418 338-420 4 270-320 4 267-321
(208-260) (210-261) (168-199) (166-200)
5 420-512 421-510 5 321-377 5 Over 321
(261-318) (262-317) (200-234) (Over 200)

Severe Storms (NOAA 2019b)

Thunderstorms — rain storms with lightning — can be dangerous by themselves and can cause
destructive, deadly flooding. When they contain strong winds, hail and tornadoes they can turn violent.
NOAA classifies a storm as “severe” when it produces wind gusts of at least 93 kph (58 mph) and/or
hail one inch in diameter (about the size of a US coin quarter) or larger and/or a tornado.

Lightning is caused by the attraction between positive and negative charges in the atmosphere,
resulting in the buildup and discharge of electrical energy. This rapid heating and cooling of the air
produces the shock wave that results in thunder.

Assessment of and planning for natural hazards 36

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