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What is weather?
Refers to the state of the atmosphere at a
specific time and place.
The one thing that you can talk to anybody
about
If you don’t like the weather just wait
around it will change in NC
What are some of the factors that affect the
weather?
Air Temperature
Temperature is the
measure of the
average amount of
motion in particles.
Wind
a natural movement of
air of any velocity;
especially : the earth's
air or the gas
surrounding a planet in
natural motion
horizontally
Humidity
The amount of water vapor present in the air
Relative Humidity -is a measure of the
amount of water vapor present in the air
compared to the amount needed for
saturation at a specific temperature
Clouds
 Made of small water droplets or tiny ice
 crystals in the air and stick to aerosol.
– Form from warm air and cool air
 Three main types are cirrus, cumulus, and
stratus.
 Other clouds are a mixture of these three
main types.
Other Cloud Types
Cirrocumulus
Stratocumulus
Cirrostratus
Cumulonimbus
More Cloud Types
Altostratus
Altocumulus
Nimbostratus
Precipitation
 Water that falls from the clouds
 Air temperature determines the form of
precipitation that falls
 4 main types of Precipitation: Rain, Sleet,
Snow and Hail
Types of Precipitation
Air Masses
 A large body of air that has
properties similar to the
part of the Earth’s surface
over which it develops.
Air Mass Map
Fronts
 A boundary between two air
masses of different density,
moisture, or temperature.
 Creates a change in weather, often
with rainstorms, thunder,
lightening, tornadoes, hail etc
Cold Front
Warm Front
Occluded Front
Stationary Front
Fronts
 Warm Front
– separates warm air from the cooler air it moves
into (6 mph, NE)
– rises over cool air masses
– develops clouds and light precipitation
 Cold Front
– cold air advancing into warm (9 to 30 mph, SE)
– pushes under warm air – rising air just ahead of
front
– vertical movement strong and thunderstorms or
blizzard
Fronts
 Stationary Front
– boundary of fronts does not move
– generally due to winds running parallel to each
other in two areas
 Occluded
– where cold front overtakes warm front
Isobars
 Isobars-connect points
of the “same”- shows
air pressure
 Examples:
temperature
(isotherms) and wind
speed
 The further away the
lines the lower the
wind speed
Seasonal
Changes
 Occur because
the earth’s axis is
tilted
 Creates opposite
seasons in the
northern and
southern
hemisphere
 Factor that
determines global
air circulation
patterns
Air Temperature
 As solar energy reaches the Earth,
equatorial regions heat up more than the
poles.
 Warm air and water at the equator travel
poleward while cold air and water at the
poles travel equatorward in an attempt to
equalize this temperature contrast.
 It is the atmosphere's continual struggle for
temperature balance that brings us our
changing weather.
http://www.usatoday.com/weather/tg/wglobale/wglobale.htm
Coriolis Effect
 The Earth is a spinning
globe where a point at
the equator is traveling
at around 1100 km/hour,
but a point at the poles
is not moved by the
rotation.
 This fact means that
projectiles moving
across the Earth's
surface are subject to
Coriolis forces that
cause apparent
deflection of the motion.
Air Pressure
 air pressure is caused by the weight of the
air pressing down on the Earth, the ocean
and on the air below
 the pressure depends on the amount of air
above the measuring point and falls as you
go higher
 air pressure changes with weather
… and Weather
 air in a high pressure area compresses and
warms as it descends
 the warming inhibits the formation of clouds,
meaning the sky is normally sunny in highpressure areas
 haze and fog might form
 the opposite occurs in an area of low
pressure
Intertropical Convergence Zone
The ITCZ is an area
of low pressure
located roughly 5
degrees North and
South of the
Equator. It is a
place where air
converges, rises,
and condenses
(forming clouds). It
is the rainiest place
on Earth!
So What Does a Hurricane Need in Order to Develop?
So a hurricane needs warm water, time to grow, and favorable upper level
winds in the troposphere. If the winds are too strong, they will blow the
hurricane apart – we call that wind shear!
Hurricane
Evolution of Hurricane Development -- Stages
Stage 1 – Tropical Wave (Depression)
Usually has begun its life off of the west coast of Africa in the ITCZ. Tropical
depressions have winds of less than 39mph, and are not given a name.
Lacks structure – no
well developed feeder
bands or eye
Evolution of Hurricane Development -- Stages
Stage 2 – Tropical Storm
At this point, the tropical storm is beginning to develop some serious structure.
Winds range from 40-73 mph. In the Atlantic, storms are given a name when they
reach this stage.
Feeder bands are
beginning to develop –
you can see the center
of the low pressure
system more easily.
Eye and eye wall still
not well formed.
Evolution of Hurricane Development -- Stages
Stage 3 – Category 1 Hurricane
Winds range from 75-94 mph.
Well developed feeder
bands. An eye begins
to form (although it is
covered in clouds).
Storm is tightening
around center.
Evolution of Hurricane Development -- Stages
Stage 4 – Category 2 Hurricane
Winds range from 95-110 mph.
Well developed feeder
bands. An eye and eye
wall are usually very
well formed. Storm
continues to tighten
around center.
Evolution of Hurricane Development -- Stages
Stage 5 – Category 3 Hurricane
Winds range from 111-130 mph.
Now considered a
“Major Storm”. Intense
flooding and building
damage will occur to
most areas on the
coast. Further inland,
the damage will still be
substantial.
Evolution of Hurricane Development -- Stages
Stage 6 – Category 4 Hurricane
Winds range from 131-155 mph.
All shrubs, signs
and trees blown
down. COMPLETE
DESTRUCTION of
mobile homes.
Extensive damage
to doors and
windows. Major
damage to lower
floors of structures
near the coast.
Evolution of Hurricane Development -- Stages
Stage 7 – Category 5 Hurricane
Winds greater than 156 mph!
Complete roof
failure on many
residential and
industrial
buildings. Some
complete building
failures with small
utility buildings
blown over or away.
Massive evacuation
of residential areas
on low ground
within 5-10 miles of
Humidity
 relative humidity is the amount of water vapor
in the air compared with the potential amount at
the air's current temperature
– expressed as a percentage, measured by hygrometer
– depends on air temperature, air pressure, and water
availability
 the Earth has about 326 million cubic miles of
water
 only about 3,100 cubic miles of this water is in
the air as water vapor > clouds > precipitation
www.rowcamp.com/photos.htm
Cloud cover
 moisture in the atmosphere forms clouds which
cover an average of 40% of the Earth at any given
time
 a cloudless Earth would absorb nearly 20 percent
more heat from the sun
 clouds cool the planet by reflecting sunlight back
into space. This is known as Albedo
However
 clouds reduce the amount of heat that radiates
into space by absorbing the heat radiating from
the surface and reradiating some of it back down
 the process traps heat like a blanket

“Cloud www.nasm.si.edu/earthtoday/ cloudlg.htm
Severe Weather - Thunderstorms
 occur from equator to Alaska
 may have hail, strong winds, lightning, thunder, rain
& tornadoes
 moist air rises due to frontal zone lifting causing loss
of heat leading to cumulus clouds with updrafts
 at 42,000 feet downdrafts and precipitation start
 may last an hour
 severe thunderstorms occur when cold front
approaches warm front (which supplies moisture
and energy)
– winds over 60 mph
– hail > 3/4 inch
Severe Weather
Thunderstorms
Lightning
Tornadoes
More Severe Weather
Hurricanes
Blizzards
Severe Weather Safety
 Watches- conditions are favorable
 Warnings- conditions already exist
 Examples- Tornadoes, Flooding,
Thunderstorms, Blizzards, Winter Mixes and
Hurricanes
Lightning
Tornadoes
 A tornado is a
violently rotating
column of air in
contact with the
ground and out
from a
cumulonimbus
cloud.
 Tornadoes are
capable of inflicting
extreme damage.
Fujita Tornado Intensity Scale
The Fujita scale, or F scale,
categorizes tornado severity based
on observed damage to man-made
structures and not on recorded wind
speeds.
F0: Gale tornado (40-72 mph); light damage.
Some damage to chimneys; break branches
off trees; push over shallow-rooted trees;
damage to sign boards.
F1: Moderate tornado (73-112 mph); moderate
damage. The lower limit is the beginning of
hurricane wind speed; peel surface off roofs;
mobile homes pushed off foundations or
overturned; moving autos pushed off the roads.
F2: Significant tornado (113-157 mph);
considerable damage. roofs torn off frame houses;
mobile homes demolished; boxcars pushed over;
large trees snapped or uprooted; light-object
missiles generated.
 F3: Severe tornado (158-206 mph); Severe damage.
Roofs and some walls torn off well-constructed
houses; trains overturned; most trees in forest
uprooted; heavy cars lifted off ground and thrown.
 F4: Devastating tornado (207-260 mph); Devastating
damage. Well- constructed houses leveled; structure
with weak foundation blown off some distance; cars
thrown and large missiles generated.
 F5: Incredible tornado (261-318 mph); Incredible
damage. Strong frame houses lifted off foundations
and carried considerable distance to disintegrate;
automobile sized missiles fly through the air in excess
of 100 yards; trees debarked; incredible phenomena
will occur.