8th Grade
Definition
Weather front – The
area where two air
masses meet and do
not mix.
Front and Weather
 Different types of fronts produce different patterns of
weather.
 There are four types of weather fronts:
1. Cold Fronts
2. Warm Fronts
3. Stationary Fronts
4. Occluded Fronts
Cold Front
 As you know, cold air is dense and tends to sink while
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warm air is less dense and tends to rise.
When rapidly moving cold air mass runs into a slowly
moving warm air mass, the denser cold air slides under
the lighter warm air.
The warm air is then pushed upward.
The front that forms is called a cold front.
Cold fronts move quickly.
Cold Front
Warm Fronts
 At a warm front, a moving warm air mass collides with
a slowly moving cold air mass.
 Because cold air is more dense than warm air, the
warm air moves over the cold air.
 Warm fronts move more slowly that cold fronts.
Warm fronts
Stationary Fronts
 Sometimes cold and warm air masses meet, but
neither one has enough force to move the other.
 In this case, the front is called a stationary front.
 Where the warm and cool air meet, water vapor in the
warm air condenses into rain, snow, or just clouds.
 If a stationary front remains stalled over an area, it may
bring many days of clouds and precipitaion.
Stationary Fronts
Occluded Fronts
 At an occluded front, a warm air mass is caught
between two cooler air masses.
 The denser cool air masses move underneath the less
dense warm air mass and push it up.
 The two cooler air masses meet in the middle and may
mix.
 The temperature near the ground becomes cooler and
the warm mass is cut off.
Occluded Fronts
Weather Front Symbols
 Cold Front: A cold front indicates a colder air
mass is moving in the direction toward which the
triangles are pointing.
 Warm Front: A warm front indicates a warmer air
mass is moving in the direction toward which the
semicircles are pointing.
 Stationary Front: A stationary front separates a
warmer from a cooler air mass.
 Occluded Front: An occluded front is drawn in
purple
Vidoe
 http://www.youtube.com/watch?v=vPC5i6w3yDI&feat
ure=related
 Using the key, can you tell me what’s happening on
this map of the United States?
Current weather
 http://www.weather.com/maps/maptype/currentweat
herusnational/index_large.html
 Use this map to describe what fronts are currently
going on in the United States.
Fun Facts
 Like fingerprints or snowflakes, no two fronts are exactly
alike. For example, the slope of a front can vary
considerably, from about 1:100 (I km of vertical distance
covers 100 km of horizontal distance) for a cold front to
about 1:200 for a warm front!
 The slope of the front is an important determinant of the
type of weather the front brings. A cold front with a very
steep slope is likely to bring a narrow band of violent
storms extending less than 100 km. A warm front with a
very gradual slope is likely to bring cloudy weather but no
storms. However, the area affected by the cloudy weather
may extend for many hundreds of km!