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Spotter Information

SKYWARN is a plan sponsored by the National Weather Service (NWS), using volunteer weather observers for reporting destructive thunderstorms or other severe, unusual, or hazardous weather conditions.

How To Become a Skywarn Spotter

If you are interested in becoming a Trained Skywarn Spotter ask your local Skywarn Chapter, Amateur Radio Group, or local National Weather Service Office, on how to become a member. Some organizations may require an Amateur Radio License to join thier local chapter. Please keep in mind that Weather Spotting can be a dangerous activity. Weather Spotting is not 'chasing'.

Severe Weather Reporting Criteria

Tornadoes, Debris Clouds, or Funnels Aloft.
Wall Clouds (Especially if Rotation is Present).
Hail 1 Inch or Larger.
Winds Greater than 58 MPH.
Rain Fall Greater than 1 Inch Per Hour Measured.
Flooding Which Poses a Hazard.
Wind or Other Storm Damage to Buildings, Crops, etc.
Hail Accumulations Which pose a Hazard or cause flooding.


Hail Size and Diameter

Hail Diameter Size Description
1/4" Pea Size
1/2" Marble Size
3/4" (Old Severe Criteria) Dime Size
7/8" Nickel Size
1" (New Severe Criteria) Quarter Size
1 1/4" Half Dollar Size
1 1/2" Walnut or Ping Pong Ball Size
1 3/4" Golf Ball Size
2" Hen Egg Size
2 1/2" Tennis Ball Size
2 3/4" Baseball Size
3" Teacup Size
4" Softball Size
4 1/2" Grapefruit Size

Wind Speed Estimates and Descriptors

Wind Speed Estimate Description
25-31 mph Large branches in motion;
whistling heard in telephone wires
32-38 mph Whole trees in motion;
inconvenience felt walking against the wind
39-54 mph Twigs break off trees;
wind generally impedes progress
55-72 mph Damage to chimneys and TV antennas;
pushes over shallow rooted trees
73-112 mph Peels surfaces off roofs; windows broken; light mobile homes pushed or overturned;
moving cars pushed off road
113-157 mph Roofs torn off houses;
cars lifted off ground

The Enhanced Fujita Scale

FUJITA SCALE DERIVED EF SCALE OPERATIONAL EF SCALE
F Number Fastest 1/4-mile (mph) 3 Second Gust (mph) EF Number 3 Second Gust (mph) EF Number 3 Second Gust (mph)
0 40-72 45-78 0 65-85 0 65-85
1 73-112 79-117 1 86-109 1 86-110
2 113-157 118-161 2 110-137 2 111-135
3 158-207 162-209 3 138-167 3 136-165
4 208-260 210-261 4 168-199 4 166-200
5 261-318 262-317 5 200-234 5 Over 200

The Fujita Scale

F-Scale Number Intensity Phrase Wind Speed Type of Damage Done
F0 Gale tornado 40-72 mph Some damage to chimneys; breaks branches off trees; pushes over shallow-rooted trees; damages sign boards.
F1 Moderate tornado 73-112 mph The lower limit is the beginning of hurricane wind speed; peels surface off roofs; mobile homes pushed off foundations or overturned; moving autos pushed off the roads; attached garages may be destroyed.
F2 Significant tornado 113-157 mph Considerable damage. Roofs torn off frame houses; mobile homes demolished; boxcars pushed over; large trees snapped or uprooted; light object missiles generated.
F3 Severe tornado 158-206 mph Roof and some walls torn off well constructed houses; trains overturned; most trees in forest uprooted
F4 Devastating tornado 207-260 mph> Well-constructed houses leveled; structures with weak foundations blown off some distance; cars thrown and large missiles generated.
F5 Incredible tornado 261-318 mph Strong frame houses lifted off foundations and carried considerable distances to disintegrate; automobile sized missiles fly through the air in excess of 100 meters; trees debarked; steel re-inforced concrete structures badly damaged.
F6 Inconceivable tornado 319-379 mph These winds are very unlikely. The small area of damage they might produce would probably not be recognizable along with the mess produced by F4 and F5 wind that would surround the F6 winds. Missiles, such as cars and refrigerators would do serious secondary damage that could not be directly identified as F6 damage. If this level is ever achieved, evidence for it might only be found in some manner of ground swirl pattern, for it may never be identifiable through engineering studies

NOTE: The Fujita Scale is based on damage, not the appearance of the funnel.


Spotter Guides and Weather Glossaries

NOAA Basic Spotters Field Guide
NOAA Advanced Spotters Field Guide
NOAA Comprehensive Glossary Of Weather Terms For Storm Spotters.
NOAA Glossary of Weather Terms, Abbreviations, and Acronyms


Copyright © 1994-2016, Southeast Wyoming Skywarn. Last Updated: January 2016.
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