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THUNDERSTORMS
and FLOODS!
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Thunderstorms
affect relatively small areas when compared to hurricanes and winter storms which sweep large areas.
A typical thunderstorm is about 15 miles in diameter and lasts for an average of 30 minutes, though since about
1980, storms in general have been of greater severity and have lasted longer; however, no statistics
have been collected to bear this out. Nearly 1,800 thunderstorms are occurring at any moment
around the world. That's 16 million each year!
Despite their small size, all thunderstorms are dangerous. Every thunderstorm produces lightning which
kills more people each year than tornados. Heavy rain from thunderstorms can lead to flash floods - another
hazard which often wrecks havoc in inhabitated areas. Strong winds, hail and tornados are also dangers associated
with some thunderstorms. Of the estimated 100,000 thunderstorms that occur each year in the U.S., only about
10 percent are classified as severe. The U.S. National Weather Service considers a thunderstorm
severe if it produces hail at least 3/4 inch in diameter with winds 58 MPH or higher or a tornado.
Flash floods/floods are considered the number one thunderstorm killer with nearly 140
fatalities each year (U.S.).
Most flash flood deaths occur at night and when people become trapped in automobiles. During a flood avoid areas subject to
sudden flooding, do not attempt to cross a flowing stream where water is above your knees, and do not attempt to drive
over a flooded road - you can be stranded or trapped; the depth of water is not always obvious! After
the flood, do not use fresh food that has come in contact with flood waters, boil drinking water before using - wells
should be pumped out and the water tested for purity before drinking, seek necessary medical care at the nearest
hospital, do not visit disaster areas, do not handle live electrical equipment or lines, use flashlights, not
lanterns or torches, to examine buildings, and report broken utility lines. Flash floods, often moving at incredible speeds,
can roll boulders, tear out trees, destroy building and bridges, and scour new channels. Killing walls of water can
reach heights of 10 to 20 feet.
Safety
Tips |
Flash Floods |
| 1 |
Get out of areas subject to flooding. This includes dips, low spots, canyons, washes, etc.
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| 2 |
Avoid already flooded and high velocity flow areas. Do not attempt to cross a flowing stream on foot
where water is above the knees. |
| 3 |
If driving, know the depth of water in a dip before crossing; the road bed may not be
intact under the water. |
| 4 |
If your vehicle stalls, abandon it immediately and seek higher ground - rapidly rising water
may engulf the vehicle and its occupants and sweep them away. |
| 5 |
Be especially cautious at night when it is
generally harder to recognize flood danger. |
| 6 |
Do not camp or park your vehicle along streams and washes, particularly during
threatening conditions. |
Safety
Tips |
Floods |
| 1 |
Keep materials on hand such as sand bags, plywood, plastic sheeting and lumber. |
| 2 |
Install check valves in building sewer traps to prevent flood water from backing up in sewer drains. |
| 3 |
Arrange for auxiliary electrical power for hospitals and other operations which are critically affected by power failure. |
| 4 |
Keep first aid supplies at hand.
| 5 |
Keep your automobile fueled; if electric power is cut off, filling stations may not be able to operate. |
| 6 |
Keep a stock of food that requires little cooking and no refrigeration as power may be off. |
| 7 |
Keep a portable radio, emergency cooking equipment, lights & flashlights in working order. |
| 8 |
Know your elevation above flood stage. |
| 9 |
Know your evacuation route's) and alternatives. |
| 10 |
Store drinking water in clean bathtubs and various containers as water service may be interrupted. |
| 11 |
If forced to leave home, time permitting, move essential items to safe ground, fill fuel tanks
to keep them from floating away, grease immovable machinery. |
| 12 |
Move to a safe area BEFORE access is cut off by flood water. |
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Straight-Line Winds which approach from one direction are responsible for most thunderstorm wind damage. These winds can and do exceed 100 MPH.
One type of straight-line wind, the downburst can cause damage equivalent to a strong tornado and can
be extremely dangerous to aviation. During the summer in western states (U.S.) thunderstorms often produce little
rain but very strong wind gusts and dust storms.
Hail causes nearly $1 billion in damage to property and crops annually (U.S.). In this, strong rising currents of air within a storm called updrafts, carry water droplets to a
height where freezing occurs. Ice particles grow in size, finally becoming too heavy to be supported by the updraft
and fall to the ground falling at speeds faster than 100 MPH for the larger ones. Tornados result in an average of 80 deaths and 1,500 injuries each year.
What Makes A Thunderstorm? Every thunderstorm needs moisture to form clouds and rain, unstable air
which is relatively warm that can rise rapidly, and something to lift the air such as fronts, sea
breezes and mountains. The life cycle of a thunderstorm has three (3) stages, the first called the developing
stage in which towering cumulus clouds indicate rising air with usually little if any rain, lasting about 10
minutes, with occasional lightning during this stage. The next stage, mature is the most likely time
for hail, heavy rain, frequent lightning, strong winds and tornados. This stage occasionally has a black or
dark green appearance and lasts an average of 10 to 20 minutes but may last much longer in some storms.
The last stage dissipating is where rainfall decreases in intensity, however, lightning and bursts
of strong winds remain a danger.
When Are Thunderstorms Most Likely? Thunderstorms are most likely to happen in the spring and
summer months during the afternoon and evening hours but can occur year-around and at all hours. Along
the Gulf Coast and a cross the southeastern and western states, most thunderstorms occur during the
afternoon. In the Plains states they frequently occur in the late afternoon and at night.
Who's At Risk? For lightning: people who are outdoors, especially in or near tall trees, in or on water, or
on or near hilltops. For flooding: people who are in automobiles when flash flooding occurs near them, and
from tornados people who are in mobile homes and automobiles.
Go to this reference for food, other supplies and survival tips needed for
Sources: National Oceanic and Atmospheric Administration (NOAA), U.S. Dept. of Commerce,
National Weather Service, Federal Emergency Management Agency, American Red Cross
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