# Thunderstorms

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Thunderstorms are very common and affect great numbers of people each
year. Despite their small size in comparison to hurricanes and winter
storms, all thunderstorms are dangerous. Every thunderstorm produces
lightning. Other associated dangers of thunderstorms include tornadoes,
strong winds, hail, and flash flooding. Flash flooding is responsible
for more fatalities--- more than 140 annually--- than any other
thunderstorm-associated hazard.

Some thunderstorms do not produce rain that reaches the ground. These
are generically referred to as dry thunderstorms and are most prevalent
in the western United States. Known to spawn wildfires, these storms
occur when there is a large layer of dry air between the base of the
cloud and the ground. The falling raindrops evaporate, but lightning can
still reach the ground.

### What to do before thunderstorms approach

1.  Know the terms used by weather forecasters:

    -   **Severe Thunderstorm Watch**--- Tells you when and where severe
        thunderstorms are likely to occur. Watch the sky and stay tuned
        to radio or television to know when warnings are issued.

    -   **Severe Thunderstorm Warning**--- Issued when severe weather
        has been reported by spotters or indicated by radar. Warnings
        indicate imminent danger to life and property to those in the
        path of the storm.

2.  Know thunderstorm facts:

    -   Thunderstorms may occur singly, in clusters, or in lines.

    -   Some of the most severe weather occurs when a single
        thunderstorm affects one location for an extended time.

    -   Thunderstorms typically produce heavy rain for a brief period,
        anywhere from 30 minutes to an hour.

    -   Warm, humid conditions are very favorable for thunderstorm
        development.

    -   A typical thunderstorm is 15 miles in diameter and lasts an
        average of 30 minutes.

    -   Of the estimated 100,000 thunderstorms each year in the United
        States, about 10 percent are classified as severe.

    -   A thunderstorm is classified as severe if it produces hail at
        least three-quarters of an inch in diameter, has winds of 58
        miles per hour or higher, or produces a tornado.

3.  Know the calculation to determine how close you are to a
    thunderstorm:

    -   Count the number of seconds between a flash of lightning and the
        next clap of thunder. Divide this number by 5 to determine the
        distance to the lightning in miles.

4.  Remove dead or rotting trees and branches that could fall and cause
    injury or damage during a severe thunderstorm.

5.  When a thunderstorm approaches, secure outdoor objects that could
    blow away or cause damage. Shutter windows, if possible, and secure
    outside doors. If shutters are not available, close window blinds,
    shades, or curtains.

## Lightning

The ingredient that defines a thunderstorm is lightning. Since lightning
creates thunder, a storm producing lightning is called a thunderstorm.

Lightning occurs during all thunderstorms. Lightning results from the
buildup and discharge of electrical energy between positively and
negatively charged areas.

The unpredictability of lightning increases the risk to individuals and
property. In the United States, an average of 300 people are injured and
80 people are killed each year by lightning. Although most lightning
victims survive, people struck by lightning often report a variety of
long-term, debilitating symptoms, including memory loss, attention
deficits, sleep disorders, numbness, dizziness, stiffness in joints,
irritability, fatigue, weakness, muscle spasms, depression, and an
inability to sit for a long period of time.

When thunderstorms threaten your area, get inside a home, building or
hard top automobile (not a convertible) and stay away from metallic
objects and fixtures.

1.  If you are **inside** a home:

    -   Avoid showering or bathing. Plumbing and bathroom fixtures can
        conduct electricity.

    -   Avoid using a corded telephone, except for emergencies. Cordless
        and cellular telephones are safe to use.

    -   Unplug appliances and other electrical items such as computers
        and turn off air conditioners. Power surges from lightning can
        cause serious damage.

    -   Use your battery operated NOAA Weather Radio for updates from
        local officials.

2.  If **outside**, with no time to reach a safe location, follow these
    recommendations:

    -   In a forest, seek shelter in a low area under a thick growth of
        small trees.

    -   In open areas, go to a low place such as a ravine or valley. Be
        alert for flash floods.

    -   Do not stand under a natural lightning rod, such as a tall,
        isolated tree in an open area.

    -   Do not stand on a hilltop, in an open field, on the beach or in
        a boat on the water.

    -   Avoid isolated sheds or other small structures in open areas.

    -   Get away from open water. If you are boating or swimming, get to
        land and find shelter immediately.

    -   Get away from anything metal--- tractors, farm equipment,
        motorcycles, golf carts, golf clubs and bicycles.

    -   Stay away from wire fences, clotheslines, metal pipes, rails and
        other metallic paths that could carry lightning to you from some
        distance away.

    -   If you feel your hair stand on end (which indicates that
        lightning is about to strike), squat low to the ground on the
        balls of your feet. Place your hands over your ears and your
        head between your knees. Make yourself the smallest target
        possible and minimize your contact with the ground. DO NOT lie
        flat on the ground.

3.  Remember the following facts and safety tips about lightning.\
    \
    **Facts:**

    -   Lightning often strikes outside of heavy rain and may occur as
        far as 10 miles away from any rainfall.

    -   Lightning-strike victims carry no electrical charge and should
        be attended to immediately. If breathing has stopped, begin
        mouth-to-mouth resuscitation. If the heart has stopped, a
        trained person should administer CPR. If the victim has a pulse
        and is breathing, look for other possible injuries. Check for
        burns where the lightning entered and left the body. Be alert
        also for nervous system damage, broken bones, and loss of
        hearing or eyesight. Contact your local emergency management
        office or American Red Cross chapter for information on CPR and
        first aid classes.

    -   "Heat lightning" is actually lightning from a thunderstorm too
        far away for thunder to be heard. However, the storm may be
        moving in your direction!

    -   Most lightning deaths and injuries occur when people are caught
        outdoors in the summer months during the afternoon and evening.

    -   Many fires in the western United States and Alaska are started
        by lightning.

    -   Lightning can occur from cloud-to-cloud, within a cloud,
        cloud-to-ground, or cloud-to-air.

    -   Your chances of being struck by lightning are estimated to be 1
        in 600,000 but could be even less by following safety tips.

> **Safety Tips:**

-   Postpone outdoor activities if thunderstorms are likely.

-   Remember the 30/30 lightning safety rule -- Go indoors if, after
    seeing lighting, you cannot count to 30 before hearing thunder. Stay
    indoors for 30 minutes after hearing the last clap of thunder.

-   Rubber-soled shoes and rubber tires provide NO protection from
    lightning. However, the steel frame of a hard-topped vehicle
    provides increased protection if you are not touching metal.
    Although you may be injured if lightning strikes your car, you are
    much safer inside a vehicle than outside.

# Tornadoes

![](media/image2.png){width="3.232638888888889in"
height="2.53125in"}Tornadoes are nature's most violent storms. Spawned
from powerful thunderstorms, tornadoes can uproot trees, destroy
buildings and turn harmless objects into deadly missiles. They can
devastate a neighborhood in seconds.

A tornado appears as a rotating, funnel-shaped cloud that extends to the
ground with whirling winds that can reach 300 miles per hour. Damage
paths can be in excess of one mile wide and 50 miles long. Every state
is at some risk from this hazard.

### Tornado facts

1.  A tornado is a violently rotating column of air extending from a
    thunderstorm to the ground.

2.  Tornadoes are capable of destroying homes and vehicles and can cause
    fatalities.

3.  Tornadoes may strike quickly, with little or no warning.

4.  Tornadoes may appear nearly transparent until dust and debris are
    picked up or a cloud forms in the funnel. The average tornado moves
    SW to NE but tornadoes have been known to move in any direction.

5.  The average forward speed is 30 mph but may vary from stationary to
    70 mph with rotating winds that can reach 300 miles per hour.

6.  Tornadoes can accompany tropical storms and hurricanes as they move
    onto land.

7.  Waterspouts are tornadoes that form over water.

8.  Tornadoes are most frequently reported east of the Rocky Mountains
    during spring and summer months but can occur in any state at any
    time of year.

9.  In the southern states, peak tornado season is March through May,
    while peak months in the northern states are during the late spring
    and early summer.

10. Tornadoes are most likely to occur between 3 p.m. and 9 p.m., but
    can occur at any time of the day or night.

### What to do before tornadoes threaten

Know the terms used to describe tornado threats:

1.  **Tornado Watch**--- Tornadoes are possible. Remain alert for
    approaching storms. Watch the sky and stay tuned to radio or
    television to know when warnings are issued.

2.  **Tornado Warning** --- A tornado has been sighted or indicated by
    weather radar. Take shelter immediately.

3.  Ask your local emergency management office or American Red Cross
    chapter about the tornado threat in your area. Ask about community
    warning signals.

4.  Purchase a NOAA Weather Radio with a battery backup and tone-alert
    feature that automatically alerts you when a Watch or Warning is
    issued (tone alert not available in some areas). Purchase a
    battery-powered commercial radio and extra batteries as well.

5.  Know the county or parish in which you live. Counties and parishes
    are used in Watches and Warnings to identify the location of
    tornadoes.

6.  Determine places to seek shelter, such as a basement or storm
    cellar. If an underground shelter is not available, identify an
    interior room or hallway on the lowest floor.

7.  Practice going to your shelter with your household.

8.  Know the locations of designated shelters in places where you and
    your household spend time, such as public buildings, nursing homes
    and shopping centers. Ask local officials whether a registered
    engineer or architect has inspected your children's schools for
    shelter space.

9.  Ask your local emergency manager or American Red Cross chapter if
    there are any public safe rooms or shelters nearby. See the "Safe
    Room and Shelter" section at the end of this chapter for more
    information.

10. Assemble a disaster supply kit. Keep a stock of food and extra
    drinking water. See the "Emergency Planning and Disaster Supplies"
    and "Evacuation" chapters for more information.

11. Make a record of your personal property. Take photographs or
    videotapes of the exterior and interior of your home, including
    personal belongings. Store these documents in a safe place, such as
    a safe deposit box.

### What to do during a tornado watch

1.  Listen to NOAA Weather Radio or to commercial radio or television
    newscasts for the latest information.

2.  Be alert for approaching storms. If you see any revolving funnel
    shaped clouds, report them immediately by telephone to your local
    police department or sheriff's office.

3.  Watch for tornado danger signs:

    -   Dark, often greenish sky

    -   Large hail

    -   A large, dark, low-lying cloud (particularly if rotating)

    -   Loud roar, similar to a freight train

***Caution:***

-   Some tornadoes are clearly visible, while rain or nearby low-hanging
    clouds obscure others.

-   Occasionally, tornadoes develop so rapidly that little, if any,
    advance warning is possible.

-   Before a tornado hits, the wind may die down and the air may become
    very still.

-   A cloud of debris can mark the location of a tornado even if a
    funnel is not visible.

-   Tornadoes generally occur near the trailing edge of a thunderstorm.
    It is not uncommon to see clear, sunlit skies behind a tornado.

4.  Avoid places with wide-span roofs such as auditoriums, cafeterias,
    large hallways, supermarkets or shopping malls.

5.  Be prepared to take shelter immediately. Gather household members
    and pets. Assemble supplies to take to the shelter such as
    flashlight, battery-powered radio, water, and first aid kit.

### What to do during a tornado warning

When a tornado has been sighted, go to your shelter immediately.

1.  In a residence or small building, move to a pre-designated shelter,
    such as a basement, storm cellar or "Safe Room or Shelter."

2.  If there is no basement, go to an interior room on the lower level
    (closets, interior hallways). Put as many walls as possible between
    you and the outside. Get under a sturdy table and use arms to
    protect head and neck. Stay there until the danger has passed.

3.  Do not open windows. Use the time to seek shelter.

4.  Stay away from windows, doors and outside walls. Go to the center of
    the room. Stay away from corners because they attract debris.

5.  In a school, nursing home, hospital, factory or shopping center, go
    to predetermined shelter areas. Interior hallways on the lowest
    floor are usually safest. Stay away from windows and open spaces.

6.  In a high-rise building, go to a small, interior room or hallway on
    the lowest floor possible.

7.  Get out of vehicles, trailers and mobile homes immediately and go to
    the lowest floor of a sturdy nearby building or a storm shelter.
    Mobile homes, even if tied down, offer little protection from
    tornadoes.

8.  If caught outside with no shelter, lie flat in a nearby ditch or
    depression and cover your head with your hands. Be aware of
    potential for flooding.

9.  Do not get under an overpass or bridge. You are safer in a low, flat
    location.

10. Never try to outrun a tornado in urban or congested areas in a car
    or truck; instead, leave the vehicle immediately for safe shelter.
    Tornadoes are erratic and move swiftly.

11. Watch out for flying debris. Flying debris from tornadoes causes
    most fatalities and injuries.

### What to do after a tornado

1.  Look out for broken glass and downed power lines.

2.  Check for injuries. Do not attempt to move seriously injured persons
    unless they are in immediate danger of death or further injury. If
    you must move an unconscious person, first stabilize the neck and
    back, then call for help immediately.

    -   If the victim is not breathing, carefully position the victim
        for artificial respiration, clear the airway and commence
        mouth-to-mouth resuscitation.

    -   Maintain body temperature with blankets. Be sure the victim does
        not become overheated.

    -   Never try to feed liquids to an unconscious person.

3.  Use caution when entering a damaged building. Be sure that walls,
    ceiling and roof are in place and that the structure rests firmly on
    the foundation. Wear sturdy work boots and gloves.

4.  See the "Recovering From Disaster" chapter for more important
    information.

### Wind "Safe Room and Shelter"

Extreme windstorms in many parts of the country pose a serious threat to
buildings and their occupants.

Your residence may be built "to code," but that does not mean that it
can withstand winds from extreme events like tornadoes or major
hurricanes.

The purpose of a wind shelter or "Safe Room" is to provide a space where
you and your household can seek refuge that provides a high level of
protection. You can build a shelter in one of the several places in your
home:

-   In your basement

-   Beneath a concrete slab-on-grade foundation or garage floor

-   In an interior room on the first floor

Shelters built below ground level provide the greatest protection, but a
shelter built in a first-floor interior room can also provide the
necessary protection. Below-ground shelters must be designed to avoid
accumulating water during the heavy rains that often accompany severe
windstorms.

To protect its occupants, an in-house shelter must be built to withstand
high winds and flying debris, even if the rest of the residence is
severely damaged or destroyed. Therefore:

-   The shelter must be adequately anchored to resist overturning and
    uplift.

-   The walls, ceiling, and door of the shelter must withstand wind
    pressure and resist penetration by windborne objects and falling
    debris.

-   The connections between all parts of the shelter must be strong
    enough to resist the wind.

-   If sections of either interior or exterior residence walls are used
    as walls of the shelter, they must be separated from the structure
    of the residence, so that damage to the residence will not cause
    damage to the shelter.

If you are concerned about wind hazards where you live, especially if
you live in high-risk areas, you should consider building a shelter.
Publications are available from FEMA to assist in determining if you
need a shelter and how to construct a shelter. Contact the FEMA
distribution center for a copy of *Taking Shelter from the Storm* (L-233
for the brochure and FEMA-320 for the booklet with complete construction
plans).