Discussion What are some ways in which weather affects your
everyday life?
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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.
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Layers of the Atmosphere
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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)
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Convection in the Atmosphere
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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 Earths surface. As temperature increases
pressure decreases. Cool air is more dense, which causes it to sink
(high pressure). As altitude increases air pressure decreases.
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Weather and Air Pressure Changes in pressure indicated a change
in weather is approaching. Low pressure systems are associated with
clouds & precipitation (lousy weather) High pressure systems
are associated with clear skies (happy weather) Steady pressure
indicates current conditions will continue. Measured with a
barometer in inches of mercury or in millibars.
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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.
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Relative Humidity Chart
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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.
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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.
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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.
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Global Winds Draw this in your notebook!!! LEARN THIS!!
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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: Earths
rotation causes winds to curve to the right in the Northern
Hemisphere and to the left in the Southern Hemisphere (its a
phenomenon)!
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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
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Clouds Clouds form when air rises, cools, and condenses. They
are classified according to their height and shape.
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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.
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Cumulus and Stratus
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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.
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Cumulonimbus and Cirrus
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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.
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The Water Cycle Earths 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.
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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.
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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.
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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.
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Air Masses
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Air Mass Locations
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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.
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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.
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Warm and Cold Fronts WARM FRONT COLD FRONT
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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 fast- moving cold air mass overtakes a slower
warm air mass. Weather is similar to, but less severe than, the
weather along a cold front.
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Stationary and Occluded STATIONARY OCCLUDED
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Weather Maps Satellite map: allow meteorologists to monitor
weather on the global scale Radar Map: uses electromagnetic waves
to monitor velocity and altitude.
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Weather Map Symbols HIGH PRESSURE SYMBOL LOW PRESSURE
SYSTEM
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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.
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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.
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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.
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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.
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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.
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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 storms center.
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Parts of a Hurricane
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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.
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When Hurricanes Occur
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Tracking Hurricanes Hurricanes can be tracked using satellites,
radar (near land), and hurricane hunters. Hurricane Hunters is the
nickname of the 53 rd 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 waters surface.
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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.
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Hurricane Paths
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Hurricane Ike
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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.
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Storm Surge Storm Surge Animation
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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.
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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
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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.
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Size of Typhoon Tip Had a diameter of almost 1,400 miles.
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Path of Typhoon Tip
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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.