(*** Please note this page is under construction ***)

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

Mobile Spotter Safety Tips Being on the road…

  • Best to spot with a partner.
  • Know where the storm is and how its moving.
  • Watch for water on the road.
  • Obey traffic laws.
  • Watch out for the other guy.
  • Always start with a full tank of gas.
  • Keep a well-maintained vehicle.


  • Severe Thunderstorm – Thunderstorm producing winds of at least 58 mph (50 kts), and/or ¾” diameter hail (or greater).
  • DOWNBURST An intense downdraft from a thunderstorm that produces damaging wind gusts of 58 mph or greater. Strong downdraft producing an outrush of damaging winds at or near the ground
  • Microburst – small scale (<2.5 miles), short-lived (<5 mins) downburst. smaller scale, but wind may be more concentrated
  • Macroburst – large scale (>2.5 miles), long-lived (>5 mins) downburst
  • Derecho – Large scale, long-lived family of downbursts, sometimes persisting hundreds of miles.
  • FUNNEL CLOUD A rotating, funnel-shaped cloud extending from a thunderstorm or towering cumulus. Spotters should report a ‘tornado’ if the funnel is in contact with the ground.
  • TORNADO A violently rotating column of air extending from a thunderstorm, in contact with the ground.
  • FLASH FLOOD WARNING Short-term flood (typically within 6 hours of the cause) which poses a threat to life and property. Flash flooding includes major small stream or urban flooding, rapidly flowing water, and dam/levee failure. A rapid rise in water, usually occurring in 12 hours or less.
  • SMALL STREAM/URBAN FLOOD ADVISORY Flooding that does not meet the flash flood criteria and should not pose a significant threat to life or property. Examples would include minor urban or small stream flooding, and standing water in low spots during or after heavy rain.
  • Watch –Atmospheric conditions are favorable (or could become favorable) for the development of thunderstorms which could produce severe weather – remain alert.
  • Warning – Severe weather has occurred or is likely to occur – take protective action.
  • Convergence: where winds from different directions meet, or fast winds meet slow winds.
  • Fronts: boundary between two air masses with different characteristics.

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


Storm spotters must also keep in mind that during a severe weather event, Stress, Excitement, 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.

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)