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monsoon
is known to many as the Summer, Southwest, Mexican or Arizona monsoon. It is also sometimes called the Desert Monsoon as a large
part of the affected area is desert.
The
North American monsoon is associated with an area of high pressure called the
subtropical ridge that moves northward during the summer months and a thermal
low (a trough of low pressure which develops from intense surface heating)
over the Mexican Plateau and the Desert Southwest of the United States. The
monsoon begins in late May to early June in southern Mexico and quickly spreads along the western slopes of the Sierra Madre Occidental, reaching Arizona and New Mexico in early July. The monsoon extends into the southwest United States as it matures in mid July when an area of high pressure, called the monsoon or
subtropical ridge, develops in the upper atmosphere over the Four Corners region, creating an easterly to southeasterly wind flow aloft. This wind
flow pattern directs moisture originating in the Gulf of Mexico, Gulf of
California and the tropical Pacific by way of northern Mexico into the region. When precipitable water values near 1.32 inches (34 mm),
brief but often torrential thunderstorms can occur, especially over
mountainous terrain. This activity is occasionally enhanced by
the passage of retrograding (westward-moving) upper cyclones and the
entrainment of the remnants of tropical storms.
As
much as 70% of rainfall in the region occurs during the summer monsoon. Many
desert plants are adapted to take advantage of this brief wet season. Because
of the monsoons, the Sonoran and Mojave are considered relatively
"wet" when ranked among other deserts such as the Sahara. This is
about the only time of year you won’t hear Wickenburg residents say “yeah it
is hot, but it is a dry heat.”
Monsoons
play a vital role in managing wildfire threat by providing moisture at higher
elevations and feeding desert streams. Heavy monsoon rain can lead to excess
winter plant growth, in turn a summer wildfire risk. A lack of monsoon rain
can hamper summer seeding, reducing excess winter plant growth but worsening
drought.
Flash flooding is a serious danger during the
monsoon season. Dry washes can become raging rivers in an instant, even when
no storms are visible as a storm can cause a flash flood tens of miles away
(never camp in a dry wash in the desert). Lightning strikes are also a
significant danger. Because it is dangerous to be caught in the open when
these storms suddenly appear, many golf courses in Arizona have thunderstorm
warning systems.
The
North American monsoon affects much of the United States and Mexico. Major drought episodes in the midwestern United States are associated with an
amplification of the upper tropospheric monsoon ridge, along with a weakening
of the western edge of the "Bermuda high" and the low-level jet
stream over the great plains.
Monsoon
Safety Tips from the American Red Cross
Before the Storm
Strikes, Know What to Expect...
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Keep an eye on
the sky. Look for darkening skies, flashes of light, or increasing wind.
Listen for the sound of thunder.
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If it has been
raining hard for several hours, be alert to the possibility of a flood.
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If you can
hear thunder, you are close enough to the storm to be struck by lightning. Go
to safe shelter immediately.
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Listen to NOAA
Weather Radio, commercial radio, or television for the latest weather
forecasts.
When a
Storm Approaches...
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Find shelter
in a building or car. Keep car windows closed and avoid convertibles.
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Telephone
lines and metal pipes can conduct electricity. Unplug appliances. Avoid using
the telephone or any electrical appliances. (Leaving electric lights on,
however, does not increase the chances of your home being struck by
lightning.)
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Avoid taking a
bath or shower, or running water for any other purpose.
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Draw blinds
and shades over windows. If windows break due to objects blown by the wind,
the shades will prevent glass from shattering into your home.
If Caught
Outside...
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If you are in
the wilderness or forest area, take shelter under the shorter trees.
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If you are
boating or swimming, get to land and find shelter immediately!
In the
Event of a Power Outage...
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Only use a
flashlight for emergency lighting. Never use candles!
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Turn off
electrical equipment you were using when the power went out.
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Avoid opening
the refrigerator and freezer.
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Do not run a
generator inside a home or garage.
If
Someone is Struck by Lightning...
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People struck
by lightning carry no electrical charge and can be handled safely.
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Call for help.
Get someone to dial 9-1-1 or your local Emergency Medical Services number.
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The injured person
has received an electrical shock and may be burned, both where they were
struck and where the electricity left their body. Check for burns in both
places. Being struck by lightning can also cause nervous system damage,
broken bones, and loss of hearing or eyesight.
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Give First
Aid. If breathing has stopped, a trained person should begin rescue
breathing. If the heart has stopped beating, a trained person should give
CPR. If the person has a pulse and is breathing, look and care for other
possible injuries.
Flash
Floods Can Take Only a Few Minutes to a Few Hours to Develop...
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A flash flood
WATCH means flash flooding is possible in your area.
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A flash flood
WARNING means a flash flood is occurring or will occur very soon.
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If driving
through a flooded area – DO NOT try to cross washes with water in them.
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If your car
stalls in rapidly rising waters, abandon it immediately and climb to higher
ground.
When a
Flood WATCH Is Issued...
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Move your
furniture and valuables to higher floors of your home.
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Fill your
car’s gas tank, in case an evacuation notice is issued.
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Be alert to
signs of flash flooding and be ready to evacuate on a moment's notice.
When a
Flood WARNING Is Issued...
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Listen to
local radio and TV stations for information and advice. If told to evacuate,
do so as soon as possible. Or if you think it has already started, evacuate
immediately. You may have only seconds to escape. Act quickly!
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Move to higher
ground away from rivers, streams, creeks, and storm drains. Do not drive
around barricades … they are there for your safety.
After the
Storm Passes...
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Stay away from
storm-damaged areas.
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Listen to the
radio and watch TV for information and instructions.
Prepare
NOW for any type of disaster...
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Build a
disaster supplies kit
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Have a family
disaster plan
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Get trained in
CPR and First Aid
For more
information about preparedness or to sign up for a class, contact the Red
Cross Grand Canyon Chapter at (602) 336-6660.
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