Mission of the NWS

“The National Weather Service (NWS) provides weather, hydrologic, and climate forecasts and warnings for the protection of life and property and the enhancement of the national economy.”

The Goal of the Spotter Program

  • To equip you (the spotter) with the tools necessary to accurately observe the weather
  • To be the eyes of the NWS where sever weather is occurring or has occurred
  • Spotters play an important role in warning operations
    • Reporting storm type or structure
    • Reporting storm impacts
    • Reporting damage, flooding or injury from storms
    • Hail reports
    • Wind reports
    • Damage reports
    • Tornado reports
    • Winter weather too
      • This information helps the NWS provide the MOST accurate warnings/watches, advisories and statements

What Do We Expect From A Spotter?

  • Stay Safe!
  • Report what YOU see and only what YOU see
  • Stay out of disaster areas unless part of an emergency response team

Why Are Spotters So Important?

  • Because Radar only gives us a piece of the puzzle
  • Looks high in the storm
  • Does not “see” tornadoes
  • Indicates hail, but NOT the exact size
  • Sometimes only shows rotation AFTER a tornado has formed

Tornado Warning Criteria

A tornado is occurring, a verified funnel cloud is reported and the NWS believes it could develop on the ground, or radar indicates a thunderstorm capable of producing a tornado.

Tornado Definitions

Tornado: Is a violent, dangerous, rotating column of air which is in contact with both the surface of the earth and the base of a thunderstorm.

Landspout: A type of tornado which is not associated with a thunderstorms mesocyclone (they form when ground based rotation is pulled into the updraft base of a thunderstorm).

Near Tornadoes

Dust Devil: Form as a swirling updraft under sunny conditions during fair weather, rarely coming close to the intensity of a tornado.

Gustnado: Form due to non-tornadic cyclonic features in the downdraft from the gust (outflow) front of a strong thunderstorm, especially one which has become outflow dominated.


Required for thunderstorm formation:

  • Moisture
  • Lift / Instability

Common Thunderstorm Types

  • Multicell ordinary storms with low severe threat. The multicell thunderstorm is the most common thunderstorm type. It is composed of multiple cells with updrafts and downdrafts at different stages in their life cycle. Although each of these individual cells in the cluster may last for only 30 minutes, the entire multicell cluster may last for several hours. Severe weather produced by the multicell thunderstorm is usually isolated and of short duration.
  • Squall line line of storms with moderate wind threat. Squall lines are simply a continuous or nearly continuous line of thunderstorms.
  • Classic Supercell rotating updraft with high severe threat. While the supercell is much less common, it does have a much higher likelihood of producing severe weather. The supercell differs from other thunderstorms in that it has one primary updraft and downdraft. The updraft and downdraft are able to maintain a near steady-state coexistence. In addition, a very important feature of the updraft is that it rotates. This rotating updraft is known as a mesocyclone. This mesocyclone in a thunderstorm can extend several tens of thousands of feet up into the storm and averages two to six miles in diameter. It is within this larger scale circulation (the mesocyclone) that tornadoes can form. There are types of tornadoes that form outside of the mesocyclone and those will be covered later. It should be noted that usually the stronger, longer-lived tornadoes are those which form within the mesocyclone. Radars do not see tornadoes the vast majority of the time. It is the larger scale rotation (the mesocyclone) which is seen by the Doppler radar.
  • Mini Supercell small storm with rotating updraft, low wind/hail threat. Mini supercells are just what the name describes. They are small supercell storms. The nature of mini supercells is that often the only severe weather they produce are tornadoes. Mini supercells can be very deceiving and difficult for a spotter to assess the real danger of the storm. To a spotter, mini supercells often appear to be benign or non-severe as they often do not produce hail or strong straight-line winds common in classic supercells. Mini supercells often move quickly and frequently form in an environment which is favorable for low cloud development and subsequent poor visibility.
  • HP (high precipitation) Supercell rotating updraft often times obscured by heavy rain, high severe threat. The HP Supercell has many of the same characteristics of the classic supercell. It does, however, have some very important distinctions. As with the classic supercell, the HP supercell is dominated by one main rotating updraft and downdraft. One notable difference however, is the presence of precipitation falling around the updraft region. In a classic supercell, most of the updraft area is nearly rain-free.
  • LP (low precipitation) Supercell – rotating updraft with light precipitation area, moderate hail and low tornado threat. Low precipitation (LP) supercells are characterized by a relative lack of visible precipitation. Structurally and visually, they have some similarities to a classic supercell. The notable difference is the relative lack of rainfall in a LP supercell. LP storms often exhibit a distinct visual appearance. The main updraft tower is often thin and bell-shaped, with a corkscrew appearance- suggesting rotation. They are capable of occasionally producing tornadoes, but have a higher tendency to produce large hail. Radar identification is often difficult relative to other types of supercells, so visual reports are very important. LP storms are most frequent in the relatively drier climates found in the high plains, but occasionally develop east into the Mississippi River Valley area. If an LP storm moves into a more favorable moisture environment, they can evolve into a classic or HP supercell.

Flash Flood Warning Criteria

  • A rapid rise out of banks flow in a river or stream that is a threat to life or property
  •  Approximately six inches or more of flowing water over a road or bridge and poses a threat to life or property
  •  Any amount of water in contact with, flowing into, or causing damage to an above ground building (does not include water seepage into basements)
  •  Three feet or more of ponded water that poses a threat to life or property

The above must occur within six hours of the causative event such as heavy rain, a dam break, or ice jam release

Spotter Positioning

Storm spotters can be either stationary or mobile. If you are a stationary spotter (for example if you spot from your home or from work), you will have no choice in your position relative to the storm you are viewing. You will have to deal with what Mother Nature gives you.  If you are a mobile spotter, then positioning is very important with respect to visibility and safety. When mobile spotting, one should always keep in mind safety. While one needs to be close enough to the thunderstorm to observe details below the updraft, a safety zone should be maintained. This will depend on the particular storm and roads available, but try to maintain a one to two mile safety zone. In the above example, we see a thunderstorm viewed from the southwest (looking northeast) at a distance not close enough to see details under the updraft. We can see the flanking line off to the right, the updraft towers on the back of the storm, and the thunderstorm anvil.

It is best (when possible) to view a thunderstorm using the right-hand rule. This means that one should be positioned so the thunderstorm is moving from one’s left to his/her right. For example, if a thunderstorm was moving to the northeast, one would want to be southeast of the storm and looking toward the west or northwest. If the thunderstorm is moving toward the southeast, one would want to be looking northeast toward the storm. In both cases, the thunderstorm would be moving toward the right with respect to the spotter. If the storm is moving to your right, then the updraft portion of the thunderstorm should be situated between the viewer and the heavier rainfall. This should give a fairly unobstructed view of the base of the updraft.  In the above example, the spotter is looking toward the west or northwest as the thunderstorm moves to the northeast. The darker area to the right is rainfall in the downdraft, while the lighter area toward the left is the updraft. In this position, the heavier rainfall will not obstruct the view of the observer. It should be noted that depending on the storm type and the atmospheric conditions, there may be times when a view of the updraft is obscured from all directions. Keep in mind that every storm and situation is different. There will be instances when your best view is from a direction totally contrary to what one would normally expect. Also, if mobile spotting, keep in mind that often times a supercell will have a tendency to curve to the right. This will force a spotter to reposition him/herself further south than what one would normally expect with a straight line or linear storm motion.

Spotter Hazard: Lightning

  • Threat with ALL storms!!
  • First strike may be the one that gets you
  • Stay inside your vehicle or indoors

Mobile Spotter Safety Tips Lightning

  • Be cautious open areas – avoid being the tallest object
  • Be careful parking on a hill or high spots
  • Don’t park too close to metal fences/power lines

Spotter Hazard: Damaging Winds

  • Non Tornadic Winds (straight line winds)
  • Various threat areas around a storm
  • Damage same/worse than a tornado

What Is A Severe Wind?

  • Officially – 58 MPH or greater
  • How can you tell the wind speed if you do not have an anemometer?
  • Damage!

Estimating Wind Speed

  • 25-31 mph large branches in motion
  • 32-38 mph – whole trees in motion
  • 39-54 mph – twigs break off, wind impedes walking
  • 55-72 mph – damage to chimneys and TV antennas, large branches broken and some trees uprooted
  • 73-112 mph – removes shingles, windows broken, trailer houses overturned, trees uprooted
  • 113+ mph – roofs torn off, weak buildings and trailer houses destroyed, large trees uprooted

Reports of 60 mph winds or higher should have some associated damage report to go along with the wind speed.


Storm spotters must also keep in mind that during a severe weather event, StressExcitement, and Tension levels are running high. This is called the SET effect, and it can alter your logic and reasoning abilities. Because of its presence, it is often very easy to over-estimate wind speeds.

A wind gust of 40 MPH during a fair weather day will not cause any great concern, but this same wind speed when experienced during a thunderstorm may seem like 60 MPH gust because of the SET effect.

When in doubt about your estimate, re-think it and try to remain calm and objective as possible. Use the table in the previous slide as a guide. Your goal is to pass real time observations with accuracy, speed, and professionalism.

Reporting Hail Size

Avoid reporting “marble size hail”. Marble sizes differ. Some marbles are big enough to be considered severe hail while others would not. Instead, reference hail size to that of a coin (penny size and larger is considered severe), sports ball, (i.e. golf ball, tennis ball, baseball), or specifically state ½ inch, 1½ inch, etc. If different size hail stones are falling, report the size of the largest stones. The best way to get an accurate hail size is, of course, to measure it with a ruler.

Hail Size Estimation
1/4” Pea                         1.75” Golf Ball
1/2” M&M (plain)        2.00” Chicken Egg
3/4” Penny / Dime       2.50” Tennis Ball
7/8” Nickel                    2.75” Baseball
1” Quarter                      3.00” Tea Cup
1.25” Half Dollar          4.00” Grapefruit
1.50” Ping Pong Ball    4.50” Softball


The Effective Spotter Report

  • Call your NWS office via phone or via Amateur Radio
  • State source of report (your identity, i.e. trained spotter)
  • Give your exact location (and location relative to the event)
  • State the start & end time of the event (be sure to differentiate between event time & report time)
  • Give an event description (be as specific and detailed as possible)
  • If event is still occurring, provide frequent updates (continuous for tornado)

How to Report

North & Central Texas Amateur Radio Frequencies:

Additional Information:

SkyWarn Info


  • Long lifetime (more than 30 minutes)
  • Organization (dominating local area)
  • Strong updrafts and downdrafts
  • Storm rotation

Supercell Clues
Mid & Upper Level Clues

  • Crisp, cauliflower texture to updraft tower
  • Rounded Updraft Tower
  • Striations (mid level cloud bands

Low Level Clues

  • Rain free base
  • Warm, moist air flowing into the storm (inflow)
  • Inflow bands
  • Shelf Cloud
  • Wall cloud
  • Tail cloud
  • Rising scud, becoming more organized with time.

Is the tornado threat increasing?

  • Circular updraft base
  • Increasing spin in wall cloud / cloud base
  • Increased inflow
  • Rapid vertical motions near wall cloud
  • Clear slot formation
  • Rain burst behind the wall cloud or a rain curtain surrounding wall cloud

What the NWS needs to know:

  • What is happening?
  • Time of event
  • Location of event (Secondary: your physical location)

Wall Clouds

  • Are usually pronounced features
  • Slope down and towards rain
  • Maintain their potion with respect to the rain (moves along with the rain)
  • Form under a smooth, flat up-draft base

Shelf Clouds

  • Slope down and away from rain
  • Changes position with respect to the rain (can move far ahead of the rain)
  • Form above a ragged, choppy downdraft base.

Things to Remember:

  • When looking for a tornado, be sure to see evidence of rotation at the ground level, not just a funnel.  Sometimes there may be no visible funnel, but a debris cloud will be visible on the ground.
  • When observing a suspicious lowering, be sure to look for persistent and organized rotation when determining if it is a tornado threat.  Thunderstorms will often have lowerings that do not rotate called scud clouds.  These can often be confused for funnels.
  • Safety comes first when spotting!  If it is dangerous to be spotting, then seek shelter quickly


Anticyclonic – Rotating in a clockwise direction when viewed from above, similar to a high pressure area. These features rotate from right to left when viewing from the ground.

Anvil – The flat, spreading top of a cumulonimbus, often shaped like a blacksmith’s anvil.

Beaver(‘s) Tail – A low cloud band with a relatively broad, flat appearance suggestive of a beaver’s tail. It is attached to a supercell’s updraft base and extends to the east or northeast.

Clear Slot – A local region of clearing skies or reduced cloud cover, indicating an intrusion of drier air; often seen on the west or southwest side of a wall cloud. A clear slot is visual evidence of a rear flank downdraft.

Cyclonic – Rotating in a counterclockwise direction when viewed from above, similar to a low pressure area. These features rotate from left to right when viewing from the ground

Downburst – A strong downdraft resulting in an outward burst of damaging winds on or near the ground. Sometimes called “straight-line winds”, downbursts may be large (macroburst) or small (microburst) in scale.

Downdraft – A column of air that rapidly sinks toward the ground, usually accompanied by precipitation as in a shower or thunderstorm.

Flanking Line – A line of cumulus or towering cumulus clouds connected to and extending outward from the most active part of a supercell, normally on the southwest side.

Funnel Cloud – A condensation funnel extending from the base of a thunderstorm, associated with a rotating column of air that is not in contact with the ground.

Glaciated – Having the appearance of a cirrus cloud, i.e., thin and fibrous in appearance. Glaciated clouds are associated with the tops of thunderstorms, especially those with weaker updrafts.

Gust Front – The leading edge of gusty surface winds from thunderstorm downdrafts; sometimes associated with a shelf cloud or roll cloud.

Gustnado – A surface-based circulation associated with thunderstorm outflow. Gustnadoes are not associated with updrafts and are not attached to cloud bases, so they are not considered true tornadoes.

High Precipitation (HP) Supercell – A supercell with a large amount of visible precipitation encircling the mesocyclone. HP supercells can be difficult to observe visually, as the precipitation often obscures the updraft-related cloud features.

Inflow Bands – Bands of low clouds, arranged parallel to the low-level winds and moving into or toward a thunderstorm. They may indicate the strength of the inflow of moist air into the storm and its potential severity.

Low Precipitation (LP) Supercell – A supercell with little visible precipitation falling from it. LP supercells often have flared-out updraft towers with striations, thus they are easy to recognize visually. However, they can be difficult to detect on radar.

Mammatus Clouds – Rounded, smooth, sack-like protrusions hanging from the underside of a thunderstorm anvil. Mammatus clouds often accompany severe thunderstorms, but do not produce severe weather.

Mesocyclone – A storm-scale region of rotation, typically around 2-6 miles in diameter and often found in the right rear flank of a supercell (or on the front flank of an HP storm).

Multiple-vortex Tornado – a tornado in which two or more condensation funnels or debris clouds are present, often rotating about a common center or about each other.

Overshooting Top – A dome-like protrusion above a thunderstorm anvil, representing a strong updraft.

Power Flash – A blue-green flash that is often a visual indication of damaging winds.

Rain Foot – A horizontal bulging of a precipitation shaft near the ground, forming a foot-shaped prominence. It is a visual indication of strong outflow winds.

Rain-free Base – A dark, horizontal cloud base with no visible precipitation beneath it. It typically marks the location of the thunderstorm updraft.

Rear Flank Downdraft – A region of sinking dry air on the back side of, and wrapping around, a mesocyclone. It often is visible as a clear slot wrapping around the wall cloud.

Scud – Small, ragged, low cloud fragments that are unattached to the main thunderstorm cloud base, but can become part of it.

Severe Thunderstorm – A thunderstorm which produces tornadoes, hail 1.00 inch or more in diameter, or winds of 50 knots (58 mph) or more. Structural wind damage may imply the occurrence of a severe thunderstorm.

Shelf Cloud – A low, horizontal wedge-shaped cloud, associated with a thunderstorm gust front. The shelf cloud is usually attached to the base of the parent cloud above it.

Squall Line – A solid or nearly solid line or band of active thunderstorms. Squall lines typically have updraft areas on the leading edge, above or just ahead of a large gust front.

Striations – Grooves or channels in cloud formations, arranged parallel to the flow of air and therefore depicting the airflow relative to the parent cloud. Striations often reveal the presence of rotation, as in the barber pole or “corkscrew” effect often observed with a rotating updraft.

Supercell – A thunderstorm with persistent storm scale rotation. Supercells are responsible for a high percentage of severe weather events – tornadoes, extremely large hail and damaging straight-line winds.

Tail Cloud – A horizontal, tail-shaped cloud (not a funnel cloud) at low levels extending from the wall cloud toward the thunderstorm’s precipitation region.

Tornado – A violently rotating column of air in contact with the ground and extending from the base of a thunderstorm.

Towering Cumulus – A large cumulus cloud with great vertical development, usually with a cumuliform or cauliflower-like appearance, but lacking the characteristic anvil of a cumulonimbus.

Updraft – A column of rising air, often associated with the active portion of a thunderstorm.

Virga – Precipitation which falls from a cloud base but evaporates before reaching the ground. Virga often has a streaky or stringy appearance as it hangs down from the cloud base.

Wall Cloud – A localized, persistent, often blocky or abrupt lowering from a rain-free base. Wall clouds suggest a strong updraft, and normally are found on the south side of the thunderstorm.

Watch – A severe weather forecast product indicating conditions are favorable for severe weather. Watches typically cover numerous counties and are valid for approximately six hours.