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Weather
The most awesome stuff ever!
Temperature
 The sun’s rays give molecules energy.
– The more energy the faster molecules move.
This causes the temperature to be higher.
– The less energy the slower molecules move.
This causes the temperature to be lower.
 Fast moving molecules transfer energy by
bumping into slow moving molecules.
– This is called conduction.
 Warm air rises and cool air sinks.
– This is called convection and is how heat is
transferred throughout the atmosphere.
Humidity
 Humidity: The amount of water vapor in the air.
 Relative Humidity: the measure of the amount of
water vapor that is in the air compared to the
amount that COULD be in the air (%)
 When the temperature is warmer evaporation
occurs more rapidly and more water vapor can be
added to the air.
– When air is completely saturated with water vapor
condensation can occur. The temperature in which this
occurs is called the dew point.
Clouds
 Clouds form when air rises, cools to its dew point,
and becomes saturated.
 Clouds can be made of small water droplets or
small ice crystals depending on the temperature.
 Clouds are classified according to the altitude that
they form in (low, middle, high)
 When “Nimbus” is attached to a cloud name it
means it is producing precipitation.
Low Clouds
 2,000 m or less in altitude
 Include:
– Cumulus (puffy cotton balls where care bears live)
– Stratus (dull gray sheets)
Middle Clouds
 2,000 m-8,000 m in altitude
 Often have the prefix “alto” such as altostratus and alto
cumulus.
 Made up of a mixture of liquid water and ice crystals
High Clouds
 Occur in air so cold that they are made up of ice crystals.
 Cirrus (wispy and feathery)
 Cirrostratus (high layered clouds that can cover the whole
sky)
Vertical Clouds
 Vertical clouds extend
through many altitude
layers.
 Cumulonimbus
(thunderstorm)
Wind
 Molecules that have been heated up move more
and become less dense and spread out.
– The causes a region of low air pressure
 Molecules that are cool move slower and closer
together becoming more dense and sink.
– This causes a region of high air pressure
*Typically air moves from high pressure areas towards low
pressure areas
-The greater the pressure difference the stronger the
wind will be.
Fronts
 A Front is a boundary
that is created
between two air
masses of different
temperatures meet.
 Four main types: Cold,
Warm, Stationary, and
Occluded.
Cold Front
 Cold air is more dense
than warm air.
 As a cold air mass
approaches a warm air
mass the cold air
moves under the warm
air mass and pushes it
up.
 Violent storms can
develop.
Warm Front
 Warm air mass
approaches cold mass.
 The warm air moves
over the cold air mass
because it is less
dense.
 A wide are of
precipitation occurs,
but not severe
weather.
Stationary & Occluded Fronts
 Stationary Front: when a warm air mass and
cold air mass meet, but neither of them
advances.
– Can stay in place for several days
 Occluded Front: A fast moving cold front
overtakes a slower moving warm front or
when a warm front overtakes a cold front
(less common)
High and Low Pressure Centers
 High Pressure:
– Air sinks
– Clockwise (Northern
Hemisphere)
– Moisture can’t rise, so no
precipitation
 Low Pressure:
– Air rises and cools
– Counterclockwise (Northern
Hemisphere)
– Clouds form with
precipitation