Download The_Weather_revised

The Weather
What are Warm and Cold Fronts?
Weather Map
Fronts
• A front is defined as the transition zone
between two air masses of different density.
Fronts extend in horizontal and vertical
direction.
• An air mass is a large body of air that has
similar temperature and moisture throughout.
Types of Fronts
• Stationary Front
A front that is not moving.
• Cold Front
Leading edge of colder air that is replacing
warmer air.
• Warm Front
Leading edge of warmer air that is replacing
cooler air.
Stationary Front
• When a warm or cold front stops moving, it
becomes a stationary front. A stationary front is
shown on a map by alternating blue and red
lines with blue triangles pointing towards the
warmer air and red semicircles pointing towards
the colder air.
A Warm Front
• A warm front: a zone where a warm air mass is
replacing a cold air mass. The air behind a warm
front is warmer and more moist than the air in
front of it. When a warm front passes through,
the air becomes warmer and more humid than it
was before.
Warm Front
• Symbolically, a warm front is represented by a
solid line with semicircles pointing in the direction
of movement.
Warm Front
• On colored weather maps, a warm front is drawn
with a solid red line. You can usually see a
change in temperature from one side of the warm
front to the other.
.
Common characteristics associated
with warm fronts.
Before
Passing
While Passing After Passing
Temperature cool-cold,
steady rise
slow warming
warmer, then
steady
Precipitation light-tomoderate
rain, snow,
sleet, or
drizzle
Winds
southsoutheast
drizzle or
none
usually none,
sometimes
light rain or
showers
variable
southsouthwest
Cold Front
• A cold front: a zone where a cold air mass is
replacing a warmer air mass. The air behind a
cold front is colder and drier than the air in front
of it. When a cold front passes through,
temperatures can drop more than 15 degrees
within the first hour.
Cold Front
The animation below shows the development of precipitation
ahead of and along a cold front. The surging blue mass
represents colder air behind the cold front (solid blue line)
while the yellow shading shows the warm moist air mass
ahead of the front. As the front moves forward, the colder air
lifts the warmer air ahead of it (red arrows). The air cools as it
rises and the moisture condenses to produce clouds and
precipitation ahead of and along the cold front.
Cold Front
• Symbolically, a cold front is represented by a
solid line with triangles along the front
pointing in the direction of movement.
Cold Front
• On colored weather maps, a cold front is drawn
with a solid blue line. There is typically a
noticeable temperature change from one side of
a cold front to the other.
.
Common characteristics associated
with cold fronts.
Before
Passing
While Passing After Passing
Temperature
warm
sudden drop
steadily
dropping
Precipitation
short period
of showers
heavy rains,
sometimes
with hail,
thunder and
lightning
showers then
clearing
Winds
southsouthwest
gusty; shifting westnorthwest
Website
• http://asp.usatoday.com/weather/w
eatherfront.aspx