Storm Spotter Reference Guide

  Storm Spotter Reference Guide   
Welcome to the Storm Spotter's Reference Guide, provided by the National Weather Service in Louisville, Kentucky, serving 49 counties across Central Kentucky and 10 counties across South Central Indiana.

Volunteer storm spotters are perhaps one of the National Weather Service's most valuable assets, and are in integral link in our warning program.   Volunteer storm spotters help to provide not only the citizens in their own community with potentially life saving information, but citizens in surrounding communities and counties as well.

The severe weather warnings issued by the National Weather Service, to a certain extent, are based upon the information you provide.  With all of the technology we now possess, including Doppler Radar, observing satellites, advanced computer workstations, and high-speed communications, trained storm spotters remain a very important link in the warning process!

To become a part of our team, we require that you attend a free training seminar on identifying and reporting severe local storms, provided by our staff in many of the counties we serve.  These classes last between 1 1/2 and 2 hours, and provide a basic understanding of thunderstorm structure, spotting techniques, reporting criteria, and procedures.  Ample opportunity is provided for feedback and questions if they arise.  New classes are being added each week. There is no need to register for any of the classes, and you may attend any class that is convenient for you.

We thank you for your time and commitment, and appreciate your willingness to help serve the citizens of your communities!

This guide is divided into several sections.  You may select any of the topics below to learn more about volunteer storm spotting, severe thunderstorms, reporting procedures, and where and how to report information!

  The Storm Spotter's Role
  • Your real-time observations of severe weather assist the National Weather Service in our warning decisions.
  • You provide an in invaluable service.
  • These observations provide a truly reliable information base for severe weather detection and verification.
  • You are helping to provide the citizens of your community with potentially life saving information.
  • The information you provide may be the reason a warning is issued, and provides credibility to the warning.
  • You don’t need a degree in Meteorology to visually evaluate and report the severity of a thunderstorm!
  • With all of the technology we now possess, the trained eye of the storm spotter is our greatest asset!

Spotter Coordination

  • It is essential that spotter networks have a clear set of policies and procedures for reporting severe weather.
  • Amateur radio operators, law enforcement and local fire departments compose the backbone of our spotter network.
  • Spotting is not a one-person job. It is difficult for a single person to accurately observe all aspects of a thunderstorm. Teamwork is essential.
  • Coordination is the key to a successful mission. Share your information with the NWS and with other spotter groups in your area.

Spotter Safety Tips

  • The National Weather Service values your safety more than the observations you provide!
  • When spotting, travel in pairs if possible. This allows the driver to remain focused, while the passenger keeps an eye on the sky.
  • Remain aware of the local environment at all times.
  • Keep a two mile buffer zone between you and the storm. Always have an escape route available.
  • Remember, lightning is one the top-ranked killers among weather phenomena. Even ahead of tornadoes and hurricanes.

Mobile Spotting Safety

  • Have an escape route in mind, remember, most storms move from west to east, however thunderstorms can move in any direction and at any speed.
  • Never ‘core punch’ a severe thunderstorm. You will often run into blinding rain and damaging hail, and may be confronted with a violent tornado at the same time.
  • Try to stay on the south side of the storm, you will often have a better vantage point.
  • Be selective about your route. Stay on paved roads if possible, isolated dirt roads and heavy rainfall don’t mix when a potential tornado may threaten your area!
  • Follow all road rules, and watch your speed.
  • Night-time spotting is difficult, it’s easy to be caught close to danger when you can’t readily observe your surroundings.

When to Begin Reporting

  • Stay abreast of the latest forecasts, severe weather watches and weather statements..
  • Listen to the “Thunderstorm Outlook” on NOAA Weather Radio.
  • Listen for the “Skywarn Activation Message” on NOAA Weather Radio
  • Coordinate with local emergency management.
   Storm Spotter Do's and Don'ts
  • Spotters Should:
    • Remain calm and collected.
    • Use common sense and spotter knowledge.
    • Report professionally.
    • Share your information with the National Weather Service and other spotter groups within your area.
  • Spotters Shouldn’t:
    • Exaggerate reports. Tell it like it is, good or bad.
    • Falsify information.
    • Misrepresent yourself or your organization.

Good versus Bad Reports:

  • Good
    • “I’m 2 miles north of Elizabethtown in Hardin County. Hail up to 1" occurred 5 minutes ago around 340 PM EDT. No damage that I can tell.”
  • Bad
    • “Yeah, I’m down here in Hardin county. We had some hail and it’s looking really bad out here.”

The first report tells us concisely and precisely what happened, and when and where exactly it did happen. It provides useful and valuable information.

The second report is not very helpful. It provides no specific information about the situation.

  • Good
    • I’m in the city of Campbellsville in Taylor County. There’s a rotating wall cloud about two miles south of my position. The wall cloud appears to be moving northeast. No funnel cloud at this time.
  • Good
    • I’m in Cynthiana in Harrison County. We had a severe thunderstorm with estimated winds of 70 mph about 10 minutes ago. Several large branches have fallen in the neighborhood and a few are lying on power lines and the power is out.
  • Good
    • There is a tornado on the ground right now just east of Paoli in Orange County Indiana in an open field. The tornado is moving due east and I can see debris.

Good reports are specific, and provide clear information about the severe weather threat.

  Information About Thunderstorms
  • A thunderstorm is a process which takes heat and moisture near the earth’s surface and transports it into the upper levels of the atmosphere.
  • At any given moment, it is estimated that there are 2000 thunderstorms in progress around the world.
  • Less than 1% of all thunderstorms produce hail ¾” in diameter or larger, and/or strong downburst winds.
  • A small fraction of storms that do become severe actually produce tornadoes.
  • No place in the United States is completely immune from the threats of severe weather. Severe weather can strike at any place, and at any time!

Thunderstorm Ingredients

  • An ample supply of Moisture
    • Preferably in the lower and mid levels of the atmosphere.
    • Gulf of Mexico
    • Pacific Ocean
  • Sufficient Instability
    • When an airmass is given an initial push upwards, it will continue moving in that direction without additional force.
  • A source of Lift
    • Differential heating
    • Orographical effects
    • Frontal boundaries
    • Drylines
    • Land/Sea breezes

Thunderstorm Life Cycle

  • The Developing Stage
    • Characterized by a single updraft within the thunderstorm.
    • As precipitation begins to fall out of the storm, a downdraft is produced.
  • The Mature Stage
    • Marked by the co-existence of an updraft and a downdraft within the thunderstorm.
  • The Dissipation Stage
    • The storm becomes dominated by the downdraft, which moves away from the storm and cuts off its inflow.
    • The downdraft may trigger new thunderstorm development as it encounters additional warm, moist, unstable air.

Thunderstorm Types

  • Single Cell Storms
    • Lifespan of 20 to 30 minutes, and are usually not strong enough to produce severe weather.
    • The storms that do become severe will produce marginally severe hail and/or brief microbursts .
  • Multi-Cell Storms
    • A group of cells at different stages of maturity, moving along as one unit, having a lifespan of several hours.
    • Moderate threat for severe weather, which include moderate-sized hail, strong downbursts, and small tornadoes.
  • Supercell Storms
    • A highly organized storm posing an inordinate threat to life and property.
    • Contains a rotating updraft, known as a mesocyclone.
    • Severe weather includes giant hail, strong downbursts, and strong to violent tornadoes.
  Key Definitions
  • Watch
    • Conditions are favorable for severe weather in or near the watch area. Watches are issued for tornadoes, severe thunderstorms and flash floods, and are for relatively large geographic areas, such as portions of or multiple states.
  • Warning
    • The severe weather event is imminent or occurring in the warned area. Warnings are issued for tornadoes, severe thunderstorms, flash floods and river flooding and are for relatively small geographic areas, such as single or small groups of adjacent counties.
  • Severe Thunderstorm
    • A storm that produces hail ¾ inch in diameter or larger and/or wind gusts of 58 mph or more.
  • Flash Flood
    • A rapid rise in water, usually within 12 hours of a period of heavy rain or other causative agent (i.e. dam break).
  • Downburst
    • A strong downdraft with an outrush of damaging wind on or near the ground.
  • Funnel Cloud
    • A rotating cone-shaped column of air extending downward from the base of a thunderstorm (or a wall cloud), but not in contact with the ground.
  • Tornado
    • A violently rotating column of air extending from the base of a thunderstorm (or a wall cloud), in direct contact with the ground.
  • Rain Free Base
    • An area of smooth, flat cloud base beneath the main storm tower, where little or no precipitation is falling.
  • Wall Cloud
    • An isolated lowering of the rain-free base found near the updraft/downdraft interface, indicating the strongest inflow or intake into the thunderstorm.
  Severe Thunderstorm Criteria
Severe Event:
  • Tornado
    • Tornado on the ground
    • Waterspout that moves onshore
  • Severe Thunderstorm/Wind
    • Convective gusts of 50 knots or more, measured or estimated from a reliable source
    • Trees blown down or uprooted (more than one)
    • Large limbs blown down (more than one)
    • Power lines blown down
    • Permanent signs blown down
    • Structural damage to businesses, homes, barns, or sheds and outbuildings
    • Home TV antennas blown down
    • Mobile homes damaged or destroyed
  • Severe Thunderstorm/Hail
    • Hail ¾" in diameter or larger
    • Windows or windshield broken by hail
    • Roofs or sidings damaged by hail
    • Hail the size of a dime or greater

Non-Severe Event:

  • Tornado
    • Tornado indicated by radar
    • Report of funnel clouds
    • Tornado-like winds
  • Severe Thunderstorm/Wind
    • Convective gusts of less than 50 knots, measured or estimated from a reliable source
    • Non-specific tree damage
    • Tree limbs blown down (no size given)
    • Generic terms such as “damaging winds”, “high winds”, or “strong winds”
    • Wind damage to crops
    • Tree or power line damage from lightning or other non-convective wind event
    • Non-specific structural damage
  • Severe Thunderstorm/Hail
    • Hail smaller than ¾" in diameter
    • Hail damage to crops
    • Non-specific references to large hail
  Where and How to Report Information
An Effective Severe Weather Report Includes the Following:
  • What?
    • What type of event occurred?
  • When?
    • When did the event happen and how long did it last?
  • Where?
    • Where did it happen? Where were you located?
  • Why?
    • Why did the event happen?
  • How?
    • How did the event happen?

Use the Following Guide to Determine the Priority of the Event:

  • Urgent Priority
    • Tornadoes (touching the ground)
    • Funnel clouds (not touching the ground)
    • Rotating wall clouds
    • Flash flooding
    • Damage to vegetation or structures
    • Severe weather related deaths
  • High Priority
    • Hail ¾-inch diameter or larger
    • Wind speed greater than 58 mph
    • Persistent wall clouds
    • Rainfall 1 inch or more per hour
  • Lower Priority
    • Hail ½-inch diameter or smaller
    • Wind speed greater than 40 mph
    • Rainfall ½-inch or more per hour

Report your Information and tell us who you are, what, when and where the event occurred, and the movement (if known) of the phenomenon.

  • Report To:
  • National Weather Service in Louisville, Kentucky
    • 24 hours a day, 7 days a week
  • Ham Radio Net Control
  • Local Law Enforcement
  • Sheriff, county dispatch, 911, etc
  • Submit a storm report: [ eSpotter ] [ Online Form ]
  Hail Size Estimates
  • Pea Size
    • 0.25”
  • Small Marble
    • 0.50"
  • Penny/Dime/Large Marble (Severe)
    • 0.75”
  • Nickel
    • 0.88"
  • Quarter
    • 1.00”
  • Half Dollar
    • 1.50”
  • Golf Ball
    • 1.75”
  • Hen Egg
    • 2.00”

  • Tennis Ball
    • 2.50”
  • Baseball
    • 2.75”
  • Grapefruit
    • 4.00”
  • Softball
    • 4.50”

  Beaufort Wind Scale
Appearance of Wind Effects
On the Water
On Land
Less than 1 Calm Sea surface smooth and mirror-like Calm, smoke rises vertically
1-3 Light Air Scaly ripples, no foam crests Smoke drift indicates wind direction, still wind vanes
4-6 Light Breeze Small wavelets, crests glassy, no breaking Wind felt on face, leaves rustle, vanes begin to move
7-10 Gentle Breeze Large wavelets, crests begin to break, scattered whitecaps Leaves and small twigs constantly moving, light flags extended
11-16 Moderate Breeze Small waves 1-4 ft. becoming longer, numerous whitecaps Dust, leaves, and loose paper lifted, small tree branches move
17-21 Fresh Breeze Moderate waves 4-8 ft taking longer form, many whitecaps, some spray Small trees in leaf begin to sway
22-27 Strong Breeze Larger waves 8-13 ft, whitecaps common, more spray Larger tree branches moving, whistling in wires
28-33 Near Gale Sea heaps up, waves 13-20 ft, white foam streaks off breakers Whole trees moving, resistance felt walking against wind
34-40 Gale Moderately high (13-20 ft) waves of greater length, edges of crests begin to break into spindrift, foam blown in streaks Whole trees in motion, resistance felt walking against wind
41-47 Strong Gale High waves (20 ft), sea begins to roll, dense streaks of foam, spray may reduce visibility Slight structural damage occurs, slate blows off roofs
48-55 Storm Very high waves (20-30 ft) with overhanging crests, sea white with densely blown foam, heavy rolling, lowered visibility Seldom experienced on land, trees broken or uprooted, "considerable structural damage"
56-63 Violent Storm Exceptionally high (30-45 ft) waves, foam patches cover sea, visibility more reduced  
64+ Hurricane Air filled with foam, waves over 45 ft, sea completely white with driving spray, visibility greatly reduced  


  • 25 - 31 mph
    • Large Branches in motion; whistling in telephone wires.
  • 32 - 38 mph
    • Whole trees in motion.
  • 39 - 54 mph
    • Twigs break off of trees; wind impedes walking.
  • 55 - 72 mph
    • Damage to chimneys and TV antennas; pushes over shallow- rooted trees.
  • 73 - 112 mph
    • Peels surface off roofs; windows broken; mobile homes overturned.
  • 113 + mph
    • Roofs torn off homes; weak buildings and mobile homes destroyed; large trees uprooted.

Developed in 1805 by Sir Francis Beaufort of England

  Fujita Tornado Intensity Scale
  • (F0) Gale Tornado (40 - 72 mph)
    • Light Damage. Some damage to chimneys; breaks branches off trees, pushes over shallow-rooted trees, damages sign boards.
  • (F1) Moderate Tornado (73 - 112 mph)
    • Moderate Damage. Lower limit is the beginning of hurricane-force winds. Peels surface off roofs; mobile homes pushed over; moving autos pushed off roads.
  • (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)
    • Severe damage. Roofs and some walls torn off well-constructed homes; trains overturned; most trees in forest uprooted; heavy cars lifted off the ground and thrown.
  • (F4) Devastating Tornado (207 - 260 mph)
    • Devastating damage. Well-constructed homes leveled; structures with weak foundations blown off some distance; cars thrown and large missiles generated.
  • (F5) Incredible Tornado (261 - 318 mph)
    • Phenomenal damage. Strong frame homes disintegrate or lifted off foundations and carried considerable distance; trees debarked.

*** IMPORTANT NOTE ABOUT F-SCALE WINDS: Do not use F-scale winds literally. These precise wind speed numbers are actually guesses and have never been scientifically verified. Different wind speeds may cause similar-looking damage from place to place -- even from building to building. Without a thorough engineering analysis of tornado damage in any event, the actual wind speeds needed to cause that damage are unknown.

Developed in 1971 by T. Theodore Fujita of the University of Chicago

  Miscellaneous Resources
 Basic Spotters Field Guide
 Advanced Spotters Field Guide
 Storm Spotter Training Presentation
 Storm Spotter Glossary
 Online Guide to Meteorology
 Microburst Handbook
 Tornadoes - Natures Most Violent Storms [ Slide Show ] [ Abbreviated Slide Show ] is the U.S. government's official web portal to all federal, state and local government web resources and services.