Transcript Weather

State Objectives 4.c, 4.e, 4.h.
Discussion
What are some ways in
which weather affects your
everyday life?
What is Weather?
 Atmosphere layer of gases surrounding Earth.
 Weather is the conditions of the atmosphere.
 Temperature
 Air Pressure
 Humidity
 Wind
 Clouds
 Precipitation
 Main cause for changes in weather is energy
from the sun.
Layers of the Atmosphere
Temperature
 Indicates the amount of heat (kinetic energy) in
the atmosphere.
 Represents the speed of the molecules.
 The higher the temperature, the faster the air
molecules are moving.
 Warmer air rises and cooler air sinks which
causes convection currents.
 Measured with a thermometer.
 Standard unit is Fahrenheit (°F)
 SI Unit is Celsius (°C)
Convection in the Atmosphere
Air Pressure/Barometric Pressure
 Air has weight because it has mass.
 Air pressure is a measure of the force of
air being exerted on a given area of Earth’s
surface.
 As temperature increases pressure decreases.
Cool air is more dense, which causes it to
sink (high pressure).
 As altitude increases air pressure decreases.

Weather and Air Pressure
 Changes in pressure indicated a change in
weather is approaching.
 Low pressure systems are associated with
clouds & precipitation.
 High pressure systems are associated with
clear skies.
 Steady pressure indicates current conditions
will continue.
 Measured with a barometer
in inches of mercury or in millibars.
Humidity
 Amount of water vapor in the air.
 Relative humidity is a percentage of the amount
of water vapor in the air compared to the
maximum amount of water vapor it can hold at
that temperature.
 The warmer the temperature the more water
vapor it can hold.
 Saturated means the air is holding 100% of
the water vapor it can hold at that temperature.
 Measured with a hygrometer or a psychrometer.
Relative Humidity Chart
Dew point
 Dew is the water vapor that has condensed
on a surface into a liquid.
 Depends on two factors:
 Amount of water vapor in the air
 Temperature near the surface
 Dew point is the temperature at which water
vapor condenses into a liquid.
Wind
 Caused by differences in air pressure
 Air moves from areas of high pressure to areas
of low pressure
 Wind Speed
 Measure of how fast the air is moving.
 Measured with an anemometer.
 Wind Direction
 Direction from which the wind is coming, NOT
the direction it is blowing
 Ex. North winds blow from N to S
 Measured with a wind vane.
Global Wind Patterns
 Blow steadily across Earth in paths that are
thousands of kilometers long
 Steer weather in certain directions (usually
west to east in the U.S.)
 Caused by thermal energy from the sun
 The sun does not heat the surface evenly
causing uneven heating of the atmosphere.
Global Winds
Types of Global Winds
 Surface winds at low altitudes:
 Trade winds: blow from east to west near
the equator.
 Westerlies: blow from west to east in the
mid-latitudes.
 Coriolis Effect: Earth’s rotation causes
winds to curve to the right in the Northern
Hemisphere and to the left in the Southern
Hemisphere.
Types of Global Winds
 Jet streams at high altitudes are bands of
strong winds (up to 350 km/h) near the top of
the troposphere at the northern and southern
boundaries of the prevailing westerlies.
 Race from west to east
Clouds
 Clouds form when air rises, cools, and
condenses. They are classified
according to their height and shape.
Types of Clouds
 1. cumulus- a low, puffy cloud that forms
on sunny days when heat from the surface
causes warm air to rise.
 2. stratus- a low, gray, sheet-like cloud that
forms when warm, moist air moves over
cooler ground. They are seen most often
during the winter and may bring steady
rain.
Cumulus and Stratus
Types of Clouds
 3. cumulonimbus (thunderheads) -
vertical clouds that may be over four
miles tall. They form where cold air
forces warm air to rise quickly.
 4. cirrus- high, featherlike clouds.
They are the highest clouds in the sky.
They do not produce precipitation.
Cumulonimbus and Cirrus
Precipitation
Precipitation – occurs when drops of water
or crystals of ice become too large to be
suspended in a cloud and fall in the form of
rain, freezing rain, sleet, snow, or hail.
The Water Cycle
Earth’s surface is about 70%
water and it exists in all three
states.
The water cycle is the constant
movement of water on Earth.
The Sun provides the energy for
the water cycle.
Parts of the Water Cycle
 1. Evaporation occurs when water
changes from a liquid into a gas after
gaining heat energy from the Sun.
 2. Transpiration is the evaporation of
water from the leaves of plants.
Parts of the Water Cycle
 3. Condensation occurs when water
vapor changes into liquid water to
form clouds or fog.
 4. Precipitation occurs when water
droplets fall to Earth.
What is an Air Mass?
 An air mass is a large body of air that
develops over a particular region.
 It has characteristics of the area over
which it develops.
 Cold, dry air masses come from Canada
and warm, dry air masses develop over
Mexico.
Air Masses
Air Mass Locations
Fronts
A front is a boundary between two
air masses.
When two fronts meet, the cold air
mass will move under the warm
air mass because the cold air is
more dense.
Types of Fronts
 1. A cold front forms when a cold air mass
pushes under a warm air mass. Cumulus
clouds form and thunderstorms may occur.
 2. A warm front forms when a warm air
mass moves up and over a cold air mass.
Cirrus and stratus clouds form and light,
steady precipitation occurs.
Warm and Cold Fronts
WARM FRONT
COLD FRONT
Types of Fronts
 3. A stationary front forms when a warm
air mass meets a cold air mass but neither
advances.
 4. An occluded front forms when a fastmoving cold air mass overtakes a slower
warm air mass. Weather is similar to, but
less severe than, the weather along a cold
front.
Stationary and Occluded
STATIONARY
OCCLUDED
Weather Maps
Satellite map: allow
meteorologists to monitor
weather on the global scale
Radar Map: uses
electromagnetic waves to
monitor velocity and altitude.
Types of Maps
Weather Map Symbols
Weather Map Symbols
HIGH
PRESSURE
SYMBOL
LOW
PRESSURE
SYSTEM
Severe Weather
 Thunderstorms: brief, intense storms
produced by rapidly rising clouds.

May produce hail
 Lightning
is huge electrical
discharges.
 A tornado is a violent, whirling wind that
moves in a narrow path over land.
TORNADO DAMAGE!!!!
Watches and Warnings
 A watch is issued when conditions are
favorable for severe weather to occur.
 A warning is issued when severe weather
has been sighted.
 The National Weather Service monitors
weather and issues watches and warnings
when appropriate.
What is a Hurricane?
 A hurricane is a low-pressure system
that forms over tropical oceans.
 Also called typhoons or tropical
cyclones.
 Named for the Mayan god Hurakan
who blew his breath across the
water.
Disturbances, Depressions, and
Storms
 A tropical disturbance is an area of
organized convection that originates in the
tropics. It has no eye or rotation.
 A tropical depression is a cyclone that has
a maximum wind speed of 38 mph.
 A tropical storm has a wind speed between
39 mph and 73 mph.
Conditions Required for Hurricane
Formation
 Warm ocean waters of at least 80° F.
 High humidity in the troposphere.
 An atmosphere that quickly cools with
altitude.
 A distance of at least 300 miles from the
equator.
 A surface system with convergent winds.
 Low wind shear. Wind shear is the rate of
wind speed or direction change with altitude.
Hurricane Formation
Parts of a Hurricane
 The eye is the circular area of calm,
relatively light winds at the center of a
hurricane. It is the area of lowest
pressure.
 The eyewall is the ring surrounding the eye
that contains the highest wind speeds.
 Rainbands are bands of heavy rain that
spiral outward from the storm’s center.
Parts of a Hurricane
Where Hurricanes Form
When Hurricanes Occur
 The Atlantic hurricane season lasts
from June 1- November 30.
 These dates include about 97% of
hurricanes.
 Most occur from August to October.
When Hurricanes Occur
Tracking Hurricanes
 Hurricanes can be tracked using satellites, radar
(near land), and hurricane hunters.
 Hurricane Hunters is the nickname of the 53rd
Weather Reconnaissance Squadron of the Air
Force Reserve. They are based in Biloxi,
Mississippi.
 Gathers data including wind direction and speed,
pressure, temperature, and humidity from the
planes altitude to the water’s surface.
Paths of Hurricanes
 Depends on where the hurricane
forms.
 Trade winds cause hurricanes to
move east to west near the equator.
 As hurricanes move north, they begin
to turn back to the east.
Hurricane Paths
Hurricane Ike
Effects of Hurricanes
 High winds
 Heavy rain and flooding
 Tornadoes after landfall
 Storm surge is the rising wall of water
that comes ashore with a hurricane. It
causes the most damage and is
responsible for 90% of deaths.
Storm Surge
 Storm Surge Animation
Naming Hurricanes
 Hurricanes are named to ease communication
between the government, forecasters, and the
public.
 Naming Atlantic storms began in 1953.
 2012 List of Names-Alberto, Beryl, Chris, Debby,
Ernesto, Florence, Gordon, Helene, Isaac,
Joyce, Kirk, Leslie, Michael, Nadine, Oscar,
Patty, Rafael, Sandy, Tony, Valerie, and William.
Rating Hurricanes
 The Saffir-Simpson scale is uses wind
speed to rate the strength of hurricanes.
 Category 1- 74-95 mph Minimal
 Category 2- 96-110 mph Moderate
 Category 3- 111-130 mph Extensive
 Category 4- 131-155 mph Extreme
 Category 5- 156+ mph Catastrophic
Strongest Hurricanes in History
 Typhoon Tip (1979) was the most intense
(lowest pressure- 870 mb) hurricane in
history.
 Hurricane Wilma (2005) was the strongest
Atlantic hurricane.
 Typhoon Nancy (1961) had maximum
sustained winds (two minute average) of
213 mph.
Size of Typhoon Tip
 Had a diameter of almost 1,400 miles.
Path of Typhoon Tip
Hurricane Katrina (2005)
 Costliest hurricane in U.S. history ($81
billion in damage).
 Fifth deadliest hurricane (1,836 deaths)
 Crossed Florida as a Category 1 but
gained strength in the Gulf of Mexico.
 Made landfall in Louisiana and Mississippi
on August 29 as a Category 3.
Path of Katrina
Katrina from Satellite
Katrina Damage
Katrina Damage
Highway 90 from Biloxi to Gulfport
Waveland, Mississippi
Pass Christian Middle School