U.S. Department of Commerce
National Oceanographic and Atmospheric Association
National Weather Service
From the National Weather Service in Key West.

This is a text version of a former NWS Key West Online Spotter training Slide Show.  Captions for photos used in the presentation are listed in the body of the text below.

Welcome, this training will teach you some basic methods of visually detecting severe weather and severe thunderstorms. Once you detect this severe weather, you will be able to report it to the NWS in Key West. Upon successful completion of the training, you will receive a Basic Spotters guide, spotter certificate, spotter ID card, contact phone number to the NWS in  Key West and other useful weather information from the NWS in Key West. Only residents of the Florida Keys of Monroe County are eligible to be a Monroe County Spotter.

There are 2 tests included in this training. One is at the end of the waterspout section and the other is at the end of slide show.

Please complete these tests and send them to Jon Rizzo at the National Weather Service in Key West, FL, at 3535 South Roosevelt Blvd., Suite 105, Key West, FL 33040 or e-mail at jonathan.rizzo@noaa.gov. Any questions or information on spotter training in your area, call Jon at 305-295-1316 ext 223.

Please include your mailing address, e-mail address if available, telephone number, and approximate location of your residence to be included in our office spotter map.

Thank you for your participation in the severe weather spotting program of the NWS.

Waterspouts

The most common form of severe weather in the Keys. Estimates indicate that 300- 400 occur each year in the Keys coastal waters.

A waterspout is defined as an intense vortex of small horizontal extent which occurs over a body of water.

There are 2 types of waterspouts, Fair Weather and Tornadic

A Tornadic waterspout develops as a tornado that just happens to occur over water. They are usually stronger and more dangerous than Fair Weather waterspouts.

Fair Weather waterspouts form in relatively calm weather and develop differently than tornadoes. They are usually less intense and dangerous than tornadoes.

Below is an example of a fair weather waterspout. 95% form along lines of rapidly developing cumulus clouds with flat, dark bases. Notice that for the most part, the weather is generally calm near the waterspout, hence the name “fair weather waterspout.”

Example of a waterspout occurring along a line of growing cumulus clouds. Spout is on right hand side, dark area under cloud on left is rain.

There are 5 stages of fair weather waterspout development.
1. Dark Spot,
2. Spiral,
3. Spray Ring,
4. Spray Vortex,
5. Decay.

The Dark Spot is the initial stage and is a circular light colored disc on the water.

Next, the Spiral stage is a distinct spiral pattern in the water around the dark spot. The funnel is just beginning to develop near the cloud base. Both the dark spot and spiral stages are difficult to see unless one is very close or above them.

The Spray ring, also called a cascade, is an area of spray being picked up from the water by the rotation. The condensation funnel between cloud bas and water becomes longer but is still not completely visible.

The Spray Vortex is when the waterspout reaches its maximum strength and becomes mature. The condensation funnel is fully visible between the cloud base and water. If the spray is being picked up from the water, then there is at least winds of 45 mph near the circulation on the surface.

The Decay stage is the beginning of the death of the waterspout. It is during this stage that rain begins to fall from the cloud associated with the waterspout. Cool, stable air at the surface is generated by the rain and this outflow from the nearby rain ends the life cycle of the waterspout. The funnel and spray become less visible and eventually are no longer visible at all.

Most waterspouts last < 10 minutes, however, stronger waterspouts can last 30 minutes or longer.

Below is an example of stages 2, 3 and 4 of waterspout formation. The spiral band is on the waters surface, around the funnel, the spray ring surrounds the dark spot near the center of circulation, and the spray vortex is surrounding the funnel near the surface.

Fair Weather waterspouts develop along an updraft of a developing cumulus cloud or thunderstorm while tornadoes develop along the interface of updrafts/downdrafts of severe thunderstorms.

An updraft is an upward accelerating column of air rising into a cumulus cloud or thunderstorm and a downdraft is an downward accelerating column of air.

The rotation of Fair Weather waterspouts begins at the surface of the water and rapidly works its way to the base of the cloud. Tornadoes begin in the mid levels of a severe thunderstorm and rapidly work their way downward towards the surface. Most waterspouts and tornadoes rotate cyclonically, (counter-clockwise) but there have been cases where they rotate anti-cyclonically (clockwise).

Notice the full condensation funnel from cloud base to water and spray vortex, just above the surface.

Mature waterspout with rain beginning to fall in the background.

Another mature, well developed, waterspout.

This is a very large waterspout south of Key Colony Beach. Most waterspouts are relatively thin and do not reach this size. Notice the smaller funnel inside the larger one.

The same large waterspout a few minutes later.

Below is an example of a decaying waterspout. The funnel is becoming less visible and defined. The dark area to the left is the beginning of rainfall, which usually signals the end of a waterspout. This spout was unusually strong and lasted nearly 40 minutes.

Another example of a decaying waterspout. Notice the bottom portion of the funnel is no longer visible and the part near the cloud appears very ragged.

Another decaying waterspout. The darker streaks behind the spout indicate rain beginning to fall.

Sometimes, multiple waterspouts can form near each other along the same line of clouds.

Another example of multiple waterspouts developing along the same line of growing cumulus clouds.

A mature waterspout, notice the dark, flat bases of the long line of cumulus clouds.

Generally, weak waterspouts only develop a visible funnel near the cloud base. There could be a circulation reaching to the waters surface, but it is not visible. If this is the case, then report it as a funnel cloud.

The peak season for waterspouts to occur in the Florida Keys coastal waters is during August and September. However, waterspouts have been observed in each month of the year.
The time of day when most waterspouts occur is in the late afternoon and early evening, generally between 5 and 7 pm. Another favored time of day for waterspout occurrence is between 10 am and noon.

Surface and low level winds (up to about 5,000 ft) are usually light, < 10 mph when fair weather waterspouts occur.

A tornadic waterspout is simply a tornado which develops over water. They are distinguished from fair weather waterspouts by their greater size, intensity and environment in which they develop. Tornadoes will be discussed in greater detail later in the lesson.

Almost all tornadoes that affect the Keys develop over water and move onshore.

Since 1950, the Keys average 2 tornadoes every 3 years.

Most tornadoes in the Keys are associated with tropical cyclones.

40% of all of the Keys tornadoes have occurred in June and 90% of them are F0 or F1 on the tornado intensity scale.

Since 1950, There has never been a F3 or higher rated tornado in the Keys.

There have been 5 F2 tornadoes in the Keys since 1950.

There have been no deaths in Monroe county due to tornadoes since 1950.

Below is an example of a tornadic waterspout. The funnel is difficult to see but it did extend to the waters surface. This tornado developed form a severe thunderstorm. The darkness around the tornado indicates there is heavy rain associated with the thunderstorm producing this tornado. Unlike “fair weather” waterspouts, the weather near a tornadic waterspout is usually turbulent and not ‘fair.”

Please answer the following questions concerning the previous information on waterspouts. Mail your responses, along with other test a the end of slide show, to Jon Rizzo, National Weather Service, 3535 S. Roosevelt Blvd., Ste. 105, Key West, FL 33040 or e-mail them to jonathan.rizzo@noaa.gov.

1. Define a waterspout.

2. What are the 2 type of waterspouts? Name at least 3 differences between the 2.

3. _____% of fair weather waterspouts form along ______ of rapidly developing cumulus clouds, with dark, flat bases.

4. Name the 5 stages of waterspout development.

5. At which stage does a waterspout become mature?

6. Can there be a circulation at the surface of the water if you do not see a condensation funnel fully extended between the base of the cloud and the water?

7. If spray being picked up by the waterspout is visible, there is at least winds of _____ mph at the surface of the waterspout.

8. T or F The rotation of a waterspout begins at the waters surface.

9. The beginning of rainfall in a cloud associated with a waterspout signals the _____ of a waterspout.

10. Waterspouts in the Keys are most likely to occur in which 2 months and during what time of day (2 peaks) are waterspouts most likely to occur?

Severe Local Storms

• Watch - conditions are favorable for the development of severe weather in or near the watch area. Issued for tornadoes, severe thunderstorms, and flash floods.
• Warning - severe weather is occurring or imminent in the warned area. Also issued for tornadoes, severe thunderstorms and flooding.
• Severe thunderstorm - a thunderstorm that produces > 3/4 diameter inch hail and/or wind gusts of 58 mph or more and/or a tornado.

• Tornado - a violently rotating column of air attached to a thunderstorm and in contact with the ground.
• Funnel cloud - a rotating funnel shaped cloud extending downward from a thunderstorm base.
• Downburst - A strong downdraft with an outrush of damaging wind on or near the ground.
• 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).

• Urgent - Tornado, Funnel cloud, rotating wall cloud, flash flooding
• High - Hail, 3/4 inch diameter or greater, wind speed 58 mph (50 knots) or greater, Persistent non-rotating wall cloud, Rainfall 1 inch or more per hour.
• Moderate - Hail ½ inch diameter or more, wind speed 40 mph or greater, cloud features suggesting storm organization, other locally defined criteria.

Severe Weather Distribution

West central Florida averages more thunderstorm days, > 100, per year than any other U.S. location. Key West averages 63 thunderstorm days per year.

The southern/central Plains and Rocky Mountains have the greatest frequency of severe hail. Hail is very rare in the Keys.

Downbursts, also known as microbursts, can occur in the key but most occur in the plains and midwest

Florida has a high frequency of tornadoes but not extremely strong tornado, f3 or higher. Most tornadoes in the Keys are associated with tropical cyclone landfalls.

Severe weather is associated with thunderstorms.
There are 3 main ingredients needed for thunderstorm development:

Moisture in middle and low levels of atmosphere

Instability, cold air over warm air

Source of lift for the air, It initiates thunderstorm development. Sources can be a boundary (fronts, outflow boundaries, drylines) topography, differential heating of land and water, tropical cyclone etc.

The keys get moisture from 3 primary sources, the Caribbean Sea, GUlf of Mexico and atlantic ocean

The larger the difference in temperature between cold air aloft (sinking) and warm air (rising) near the surface, the greater the instability and potential for severe thunderstorm development

The Cumulus stage is the first stage in the life cycle and it is here that the updrafts (upward moving currents of air) develop, reaching 20,000 feet. All motion is upward at this time.

Example of clouds in the cumulus stage

Mature Stage of a Thunderstorm
Storm has both updraft and downdrafts . Precipitation is occurring in the downdraft area. Some of the precipitation evaporates before hitting ground and drags air with it, creating the downdraft. The storm is at its strongest during this stage.

Example of thunderstorm in mature stage. The sharply defined cloud mass on the left indicates the updraft area of the storm. Top of storm is called an anvil.

Dissipating Stage
Eventually, excessive rainfall and downdraft will fall through the updraft, choking off the updraft. Storm gradually dissipates.

Example of thunderstorm in dissipating stage. Note fuzziness in anvil and updraft area.

All thunderstorms produce lightning. In fact, the sound of thunder is produced by the rapid expansion of air, due to intense heating, surrounding a lightning bolt.

Lightning ranks as the #2 killer among weather phenomena in the U.S.

Florida usually leads the nation in lightning related deaths each year.

The west central coast of Florida annually records the most lightning strikes.

Most lightning strikes are cloud to cloud but some are cloud to ground and these are the most dangerous.

Severe weather formation needs strong updrafts. One clue which indicates whether or not a thunderstorm has a strong updraft is an overshooting top, seen below rising above the rest of the cloud.

A thunderstorm which has a cumuliform anvil at its top also has a strong updraft. This storm has a thick crisp edged anvil (top).

Thin cirriform anvils indicate a thunderstorm with a weak updraft. The anvil has a wispy appearance and its edges are not sharply defined.
 

This is a strong updraft tower seen in the middle levels of a thunderstorm. Notice the sharp outline and cauliflower appearance of the cloud.

Below is an example of a weak updraft. The storm has sharp outlines but also has a soft, mushy appearance, suggesting severe weather is unlikely.

Below is a flanking cloud line. It suggests a well organized storm, necessary for persistent severe weather.

A rain free base is low flat cloud base from which little rain is falling. It marks the primary inflow and updraft area of the storm. Just to the north and east of this area is preferred for severe weather formation.

A Wall Cloud is an abrupt, isolated lowering of the rain free base. It marks the storm’s strongest updraft area and the #1 location of severe weather, especially when it is rotating.

There are 4 basic types of thunderstorms

Single cell thunderstorms have only one downdraft and updraft. They are generally weak, short lived and poorly organized. Severe weather is rare.

Multicell cluster storms are the most common. They consist of a series of cells moving along as 1 unit. Each cell progresses through the life cycle and takes turns being the dominant one. Mature cells near the center are favored areas of severe weather, but severe weather is not common.

Multicell line storms are also called squall lines. They are a long line of storms with a gust front (outflow boundary) along its leading edge. Downbursts are the most common type of severe weather associated with squall lines.

The supercell is the strongest and most organized type of thunderstorm. They are rare but produce severe weather. Supercells have a mesocyclone, small scale rotation inside the storm associated with the updraft. The mesocyclone allows for severe weather production and persistence.

Supercell Structure and Appearance
Side view diagram of a Supercell. Storm is moving left to right.

This supercell Storm is 10-15 miles away looking south. Notice sharp edged anvil and hard texture in storm tower.

Close look at a supercell. View is to southwest. Rain free base and wall cloud are visible. Not a safe place to be since large hail is probably nearby.

Another close view of a supercell, towards northwest. Rain free base, wall cloud and a large tornado are visible.

View is to the northwest. Wall cloud is under main storm tower. Heavy rain and hail are to the right. Rain free base is to the left.

Example 1. View is to the southwest.

Example 2. View is to the northwest. This wall cloud has a well developed tail cloud which extends from wall cloud toward rainfall. It marks inflow of air from precipitation area to wall cloud.

Another example of a wall cloud with a tail. View is to the northwest.

Wall clouds can form with other types of storms, but are most common with supercells.
Wall clouds are not that rare, but less than 1/4 of all wall clouds observed produce tornadoes.
If a storm is organized enough to produce a wall cloud, it has a good chance to produce other types of severe weather such as strong winds and hail.
Persistent rotation is a good way to determine if a wall cloud will produce a tornado.

Downbursts/microbursts are severe winds at the surface produced by severe thunderstorms. They are very dangerous to aviation.

Below is an approaching macroburst or large scale downburst along the leading edge of fast moving squall line. Ahead of the downburst are “mammatus” clouds. They are often associated with severe weather.

An example of a wet microburst in its formative stage, dark glob of heavy precipitation descending from cloud base.

The previous microburst reaches the ground a few minutes later, resulting in severe wind gusts at surface.

The microburst dissipates. Notice the curl of the microburst on left hand edge of precipitation. Entire sequence occurred in about 5 minutes.

Below is an example of a rain foot, a pronounced outward deflection of precipitation near the ground which marks strong outflow winds (on the left side of the rain area). This is the main way of identifying a microburst.

Hail is rare in the Keys, especially large hail. This is mainly due to the normally high freezing levels in the tropical climate of the Keys. The strength of the updraft determines the hail size. Any size hail in the Keys should be reported as an updraft strong enough to produce hail will likely be strong enough to produce severe winds at the surface.

Tornado Life Cycle

Stage 1: Developing stage of a tornado with a rotating wall cloud

The tornadic circulation continues to develop. Condensation funnel makes its appearance. The visible funnel does not have to touch ground. If visible funnel extends ½ way or more down to ground, tornadic winds have probably reached the ground. If less than ½ way down, then winds are not likely on the ground and report as a funnel cloud.

Tornado entering stage 2: the mature stage. Tornado is the most dangerous in this stage with maximum winds.
Another example of a mature tornado.

tornado entering the 3rd stage: the dissipating stage. Funnel decreases in size and circulation weakens. Still dangerous.

The final stage of a tornado life cycle is called a “rope stage.” Condensation funnel becomes tilted and shrinks to a contorted rope-like configuration.

Some tornadoes do not go into the rope stage, the circulation simply loses contact with the ground and the funnel lifts into a bowl shaped lowering. This is a mature stage of a tornado.

Here is the dissipating stage of the tornado a few minutes later. The visible funnel evolved into the bowl-shaped lowering in the center of the screen.

Tornado Classifications and Variations

Weak Tornadoes may not be associated with mesocyclones. Typically only last a few minutes and are difficult to detect and warn for. Most waterspouts will fall into this category.

Strong Tornadoes are typically associated with mesocyclones. Easier to detect than the weak ones but still rely heavily on spotter reports.

Violent Tornadoes are rare but account for most of the deaths associated with tornadoes. Almost always associated with a mesocyclone.

Many strong/violent tornadoes can develop as multiple vortex tornadoes with one central larger tornado and smaller tornadoes rotating around it.

Another multiple vortex tornado with the smaller vortices visible to the left of the large one.

As discussed earlier, some condensation funnels do not reach the ground. It is important to look for dirt/debris rotating on the ground beneath the funnel when reporting a tornado.

Most tornadoes that occur with non-supercell tornadoes probably appear in the form of landspouts. Landspouts form similar to waterspouts and are difficult to detect on radar.

Tornado/Wall Cloud Look Alikes

Sometimes rainshafts are mistaken for tornadoes. Spotters must look for other clues of a severe thunderstorm, none here.
 

This rainshaft is located where a tornado could be, but one is not present. There is no debris or rotation indicated near the ground.
 

In this case, one needs to look for a few minutes or so to determine if there is rotation in the funnel. This is actually a column of smoke.

Scud clouds (front left) are small, low clouds detached from a nearby thunderstorm. Sometimes, they can look like a wall cloud. A wall cloud must be attached to the cloud base and persistent.

Roll clouds form along gust fronts, ahead of thunderstorms. They can be mistaken for wall clouds. Usually indicate strong but not severe winds. Note rain foot in this example indicating a possible microburst.

Shelf clouds form similar to roll clouds but have more of a wedge shape. They are more common than roll clouds and indicate strong downburst winds, but are not favored areas for tornado formation.

Some shelf clouds look like wall clouds

There 3 primary differences between shelf and wall clouds.

One is that wall clouds slope from the cloud base toward the ground while shelf clouds are flat.

A wall cloud can be rotating while a shelf cloud has movement in one horizontal direction.

Wall clouds signify a severe thunderstorm with the potential of a tornado while shelf clouds can indicate strong downburst winds but do not always indicate a severe thunderstorm.

Shelf Cloud Wall Cloud

Supercell Variations

Heavy Precipitation (HP) Supercells
As the name implies, HP supercells produce a tremendous amount of precipitation, making it difficult to spot severe weather signatures.
HP Supercells are found mainly in the southeastern U.S. There is a classification known as the Low Precipitation Supercell (LP) but those occur in the much drier western states.
Never drive through precipitation of a supercell thunderstorm to see if there is a tornado. Large hail and severe winds are likely even if there is no tornado.

Below is a schematic diagram of a HP supercell. Striations, inflow band and mid level cloud bands are all ways to infer storm rotation if tornado, wall cloud etc. are not visible due to heavy precipitation. Storm is moving toward right side.

Example of a HP supercell. Main storm tower has a barrel shape and striations, indicating storm rotation and mesocyclone.

Another example of a HP supercell. Inflow band (beaver tail) is evident from center to middle right of screen View is toward the west.

A few minutes later, this tornado developed .

Unusual Variations of Supercells

Cyclic Supercells produce more than one mesocyclone and tornado during their lifetime. Tornado near center is dissipating while a new wall cloud is forming to the right.

A few minutes later, the wall cloud was better developed, suggesting that a new tornado might be forming.

The old tornado is in its rope stage and a new tornado is increasing in intensity. This cell actually produced a 3rd tornado later. New tornadoes usually form 2-4 miles east of the old tornado.

Gustnados are vortices that develop in a gust front’s outflow as it moves across the ground. They are not associated with the updraft area of the storm and generally do not extend up to the cloud base. They can be a threat and should be reported.

Spotting at night is obviously difficult. Lightning flashes, exploding transformers and power lines, roar of tornadoes and wind and large hail can be used to detect severe weather at night. Note shadow to the right of lightning bolt.

Lightning has illuminated what appears to be a wall cloud.

2. Define a severe thunderstorm.
 

3. Name the types of severe weather you report to the NWS and the priority in which they should be reported.
 

4. T or F Hail of any size occurs frequently in the Keys.

5. Name the 3 stages of the thunderstorm life cycle.

6. What are the 3 stages of the tornado life cycle?
 

7. T or F Most tornadoes in the Keys are associated with tropical cyclones making landfall.

8. Thunderstorms are divided into 4 categories, single cell, multicell cluster, multicell line and supercell. Which of these are commonly called squall lines? Which always produce severe weather?
 

9. T or F Lightning occurs in all thunderstorms.

10. Thunderstorms need strong __________ to form severe weather.

11. T or F If a condensation funnel of a tornado or waterspout is at least ½ way down between the cloud base and surface, it should be reported as a tornado or waterspout even if you can not see it at the surface.

12. T or F If a condensation funnel is less than ½ way down between the cloud base and surface, it should be reported as a funnel cloud.

In the following pictures, identify the features that would suggest a possible severe storm or updraft organization. Some pictures may not have any of these features.