What kind of weather would a continental tropical air
mass that formed over northern Mexico bring to the
southwestern U.S?
Fronts
Front - boundary between 2 different air
masses. Fronts usually bring some type of
precipitation.
Cold Front
Cold front – rapidly moving cold air overtakes
the slower moving warm air; The warm air
quickly rises allowing water vapor to condense.
Thunderstorms and severe weather are
common at these fronts. (Draw a picture of a
cold front.)
Cold Front
On a weather map a cold front is represented
by blue triangles.
Warm Front
Warm front - warmer air slowly moves over
colder air and replaces it; Leads to long periods
of steady rain or snow. (Draw a picture of a
warm front.)
Warm Front
• On a weather map a warm front is
represented by red semi-circles.
• warm and cold front animations
• cold front precipitation
• warm front precipitation
STAtionary Front
• Stationary front - a cold front and a warm
front meet, and neither can move the other
out of the way; creates days and days of the
same weather (rain or dry spells).
(Draw a picture of a stationary front.)
STAtionary Front
• On a weather map a stationary front is
represented by alternating red semi-circles
and blue arrows pointing in opposite
directions. stationary front animation
Occluded Front
Occluded front – a warm air mass is trapped
between a cool air mass and a cold air mass.
The warm air is cut off from the surface. This
leads to heavy rain. (Draw an occluded front.)
Occluded Front- “trapped”
Occluded Front
• On a weather map, an occluded front is
represented by purple semi- circles and
arrows pointing in the SAME direction.
Pressure Systems
Low Pressure Systems
• Winds blow into low pressure areas
• Warm, moist air will rise, causing cloud formation
• Weather is usually cloudy or stormy. Cloudy nights can
be warmer than clear nights because clouds trap heat
absorbed by Earth during the daylight hours.
Pressure Systems
– High Pressure Systems
• Winds blow away from high pressure areas
• Sinking motion of air makes it difficult for clouds to
form
• Weather is usually clear and sunny.
What do you notice around the H’s and L’s?
Fronts can bring severe weather:
• Thunderstorms
• Tornadoes
• Hurricanes
- Storms
Thunderstorms
• Thunderstorms are brought by cumulonimbus
clouds.
Thunderstorm Facts:
• A thunderstorm forms when warm, humid air
rises rapidly within a cumulonimbus cloud.
• Thunderstorms are LOW pressure systems.
• A drop in barometric pressure (the measure of
air pressure) usually indicates a storm is
approaching.
Examine how barometric pressure changes with
weather conditions.
Put the following sentences in order to
create a thunderstorm:
1. These small water droplets collide to form larger ones.
2. Cold air meets warm air and pushes the warm, less dense air
upward.
3. Raindrops cool the air around them.
4. This updraft creates winds associated with thunderstorms.
5. Warm, moist air cools rapidly and condenses forming clouds
that contain water droplets.
6. Larger droplets fall from cloud toward earth’s surface.
7. This cool air becomes denser and sinks, allowing the warm
air at the surface to create an updraft as it rises.
The Thunderstorm Song
http://www.youtube.com/watch?v=7nZlGg59M
Rw
Tornadoes
• Tornadoes are violent, whirling winds that
form over land.
Tornado Facts:
1) Usually form from severe thunderstorms
2) Not all thunderstorms make tornadoes, conditions
have to be just right!
3) Different winds moving at different speeds in
different directions and at different heights cause the
air to start spinning (like a paper towel tube).
4) These different winds cause a rotating
column of wind that spin vertically.
Tornado Facts:
5. Tornadoes are the fastest moving storms.
6. A tornado is not very wide and does not stay on the ground
very long (few seconds to a few minutes)
7. Most tornadoes occur in an area called “tornado alley”
because warm moist air masses from the southeast meet cold
dry air masses from the north central us.
8. Most happen in the spring and early summer.
- Storms
Tornado Alley
- Storms
Tornado Formation
• Tornadoes can form when warm, humid air
rises rapidly in thick cumulonimbus clouds—
the same type of clouds that bring
thunderstorms.
Tornado Clips
• Tornado Wind Patterns
• https://www.youtube.com/watch?v=2GWtfb5
l8iA
The Fujita-Pearson Scale
• The Fujita scale (F-Scale), or Fujita-Pearson scale, is a scale
for rating tornado intensity, based on the damage tornadoes
inflict on human-built structures and vegetation.
•
BBC NEWS | Special Reports | Animated guide: Tornadoes
Hurricanes
• Hurricanes are large, swirling storms that form
over the ocean. They are the most powerful
storms. Warm, moist air must be present for
a hurricane to develop.
Hurricane Facts
1)
2)
3)
4)
5)
6)
7)
Hurricanes are a LOW pressure system.
Start as tropical storms; renamed hurricanes if wind speeds reach 73
mph.
Form over warm ocean water near the equator; the warm water and
warm moist air supplies its power. It will only lose strength if it loses
heat or loses moisture.
Because of the Coriolis Effect, most hurricanes in the Atlantic travel east
to west. The hurricanes that affect the Southeast U.S. usually originate
off the coast of Africa.
Eye of hurricane – area in storm that is very calm, with very lowpressure and little or no winds
Most happen in late summer or early fall.
Named according to where it forms:
Hurricane – Atlantic Ocean
Typhoon – Pacific Ocean
Cyclone – Indian Ocean
http://www.nhc.noaa.gov/aboutnames.shtml
- Storms
Structure of a Hurricane
In a hurricane, air moves rapidly around a lowpressure area called the eye.
Hurricanes
• http://www.youtube.com/watch?v=SNEG4YKE
lgY
• http://www.youtube.com/watch?v=HJydFJOR
Wf4
Severe Weather Overview
Thunderstorms
Hurricanes
Tornadoes
Forms over land or water
Caused by warm
wet air rising quickly
over cold dry air
LOW
pressure
Forms over warm water
Forms out of a
Thunderstorm
Starts out as thunderstorm,
Then air at different heights,
going in different speeds in
different directions begins to
spin and lift vertically
LOW
pressure
Caused by warm
wet air from oceans
rising into the
atmosphere
LOW
pressure
Resources
• Petroleum is an
example of a nonrenewable
resource.
Resources
• Biomass is an example
of a renewable resource/
alternative to fossil fuels.
• Alternative fuels are
important because fossil
fuels are not renewable,
and we need other
choices for energy.