Transcript Severe Weather

Ch 21 Understanding Weather
•Water in the Air
•Air Masses and
Fronts
•Severe Weather
Water in the Air
•The Water Cycle
•Evaporation
•Condensation
•Precipitation
•Runoff
Water in the Air
•Humidity- the
amount of water
vapor in the air
Water in the Air
• Dew point- the temperature
to which air must cool to
become saturated.
• Saturated- when air holds all
the water vapor it can at a
given temperature
Clouds
• Cumulus- puffy white clouds
with flat bottoms
• Stratus- clouds that form in
layers
• Cirrus- feathery, wispy white
clouds at high altitudes
Air Masses and Fronts
•Cold Front- a fast-moving
cold air mass moves under
less dense warm air,
pushing it upwards
•Results in thunderstorms,
cooler weather
Air Masses and Fronts
•Warm Front- warm, less
dense air moves over the
cold, denser air, bringing
drizzly rain and then
clear warm weather
Air Masses and Fronts
•Occluded Front- a warm air
mass is caught between two
colder masses, resulting in
cool temperatures and lots
of precipitation
Air Masses and Fronts
•Stationary Front- cold
and warm air masses
meet but do not have
the force to create
storms
Severe Weather
• Thunderstorms- heavy rainstorms with
strong winds, lightning and thunder
• Lightning- an electric discharge that takes
place between a positively charged area
and a negatively charged area
• Thunder- the sound caused by the rapid
expansion of air along the lightning strike
Severe Weather
• Tornado- a small, spinning column
of air that has high wind speed
and touches the ground
• Hurricane- a large, spinning
tropical weather system with wind
speeds of at least 119 km/hr
Severe Weather
• How does a tornado form?
• Wind moving in two different
directions causes a layer of air in
the middle to spin like a roll of
toilet paper. It works it’s way to
the bottom of the cloud and
eventually to the ground.
Severe Weather
• How does a Hurricane form?
• It’s a group of thunderstorms that
form over the oceans. Wind that
travels in different directions
causes it to spin. Energy is
gathered from warm waters.
Severe Weather
• A weather forecast is a prediction
of weather conditions over the
next 3-5 days.
• A meteorologist is a person that
observes and collects data on
atmospheric conditions.
Forecasting Weather
• Meteorologists use a barometer to
measure air pressure and an
anemometer to measure wind
speed.
• Weather balloons carry radio
transmitters that send
measurements to the weather
stations