Download Weather

Weather
and how it affects us…
Weather
• Weather refers to the
state of the atmosphere
at a specific time and
place. It describes
conditions such as air
pressure, wind,
temperature, and
moisture in the air.
Can you find any storms on this image?
Weather Factors
Air temperature
• Air temperature is caused
by molecules that make up
the air. Air is a combination
of 3 gases: oxygen,
nitrogen, and CO². If the air
molecules are moving
quickly then the air feels
warm. If the molecules are
moving slowly, the air feels
cold.
• Thermometers are used to
measure temperature. They
can measure in °C (Celsius)
and °F (Fahrenheit).
Vostok, Antarctica reached a chilly 129°F
below zero in 1983!
El Azizia in Libya reached a scorching
139°F in 1922!
Weather Factors, cont.
Wind
• Air moving in a specific
direction is called wind.
• As the sun heats air in the
atmosphere, the air
expands and becomes less
dense. This air has low
atmospheric pressure.
Cooler air is heavier and
tends to sink thus having
high pressure. Wind results
when air moves from areas
of high pressure to areas of
low pressure.
• A barometer measures
atmospheric pressure.
The breeze you often feel on the beach is cool
air (high pressure) from the ocean rushing
toward the warmer air (low pressure) on the
beach.
Weather Factors, cont.
Humidity and Dew Point
• Evaporation is a stage of the water cycle that results when
heat causes water on the ground to become a gas (water
vapor) and rise into the atmosphere.
• Humidity is the amount of water vapor in the air. If the
temperature is cooler, there is less water vapor in the air. If
the temperature is warmer, there will be more water vapor in
the air.
• Relative humidity is the percent of water vapor that air is
holding. If the air is holding all of the water vapor it can, the
relative humidity is 100%.
• Dew point is the point at which air is saturated with water
vapor and condensation forms. Water vapor condenses
(becomes a liquid) when the air is cooler.
Weather Factors, cont.
Clouds
• Clouds form when warm air
is forced upward, and it
expands and cools. As the
air cools, the amount of
water vapor needed for
condensation to occur
decreases. When the
relative humidity reaches
100%, water vapor starts to
Cumulus clouds are puffy, white clouds with
condense and collect
around small particles of flat bases that can tower to great heights.
dust or salt in the air. These They can indicate fair weather or storms.
water droplets form clouds.
Weather Factors, cont.
Precipitation
• Precipitation is water
falling from clouds.
Precipitation occurs when
water droplets combine and
are large enough to fall
back to Earth.
• The 4 main types of
precipitation are:
rain, sleet, snow, and hail
Hailstones can be as small as a few cm
across or larger than a softball!
Weather Patterns
Air Masses
• An air mass is a large
body of air that has
properties that are
similar to the area it
forms over. The United
States is affected by 6
major air masses
throughout the year.
Weather Patterns, cont.
Air Masses, cont.
• When 2 air masses having different densities,
moisture, or temperature touch, the boundary
is called a front.
• Clouds, precipitation, and storms can form at
frontal boundaries.
• The 4 types of fronts include: warm, cold,
stationary, and occluded.
Weather Patterns, cont.
Fronts, cont.
• On a weather map, a
cold front will be
illustrated by a blue
line with triangles. A
warm front will have a
red line with
semicircles.
An approaching cold front will always push
warm air up creating a warm front!
Weather Patterns, cont.
Occluded and Stationary Fronts
• An occluded front involves 3
different air masses of different
temperatures and is shown on
maps as purple lines with
triangles and semicircles
• A stationary front occurs when
then boundary between air
masses stops advancing. It is
shown on maps with an
alternating red and blue line
that has red semicircles
pointing toward the cold air and
blue triangles pointing toward
the warm air.
Severe Weather
Thunderstorms
• Thunderstorms include
heavy rainfall, lightning,
thunder, and possibly
hail.
• Thunderstorms occur in
warm, moist air masses
and along fronts.
The temperature inside a bolt of lightning can
reach 50,000 °F…hotter than the Sun’s surface!
Severe Weather, cont.
Tornadoes
• Some of the most severe
thunderstorms produce
tornadoes.
• A tornado is a violent, whirling
wind that moves in a narrow path
over land.
• Tornadoes occur during
thunderstorms when wind at
different heights blows at
different directions and speeds.
These varying speeds can create
a rotating column that can
become a funnel cloud.
• When a funnel cloud touches the
ground, it is called a tornado.
Severe Weather, cont.
Hurricanes
• The most powerful type of storm is
the hurricane. It is a large,
swirling low pressure system that
forms over the warm Atlantic
Ocean. It must have wind speeds
of at least 119 mph to be
considered a tornado.
• A hurricane develops its strength
using the warmth and moisture of
the Atlantic Ocean. When it hits
land, the lack of moisture causes
the storm to lose energy and it
disappears.
Hurricane Katrina in 2005