Transcript Weather Front Symbols

October 19, 2009
• DoNow: Hand in the Isobar Lab.
– Which is more dense- humid or dry air?
– What happens to air that is less dense?
Homework: Study for the quiz on Air
pressure/weather instruments on Thursday
What is an air mass?
• a HUGE body of air that has similar
temperature, humidity and air pressure
throughout
• they are classified by their temperature
and humidity
• the temperature and humidity of an air
mass depends on where it formed
Global Air Masses
Air Masses that impact the US
Air Masses that impact the US
Fronts
• The area where air masses meet but do
not mix becomes a front.
• The collision of the air masses at a front
often causes storms and changeable
weather.
• There are four major types of fronts: cold,
warm, stationary, occluded.
Weather Front Symbols
1.
2.
3.
4.
5.
6.
7.
8.
Cold front
Warm front
Stationary front
Occluded front
Surface trough
Squall line
Dry line
Tropical wave
The arrows and circles
point in the direction
the front is moving.
Warm and Cold Fronts
Cold Front and Stationary Front
Occluded Front
Fronts and Clouds in USA
An advancing cold front brings a cooler, less humid air
mass in summer but frigid air in winter. The warm air mass
is lifted on a steep slope, which can cause severe weather.
A warm air mass can advance only if the cold air mass in front of it is
already moving. The gentle slope of the warm air mass rise creates
steady and widespread precipitation.
The warm/cold boundary exists overhead as you move into
the cold air mass.
Squall Lines
• a line of thunderstorms that develops
ahead of and parallel to a cold front or
a dry line
• storms first develop where there is
moisture, instability and lift
• squall line will sustain itself by
producing its own lift and will continue
to form new cells toward the south and
east
A very nasty looking
squall line is
pictured here.
A shelf cloud such as this one can
be a sign that a squall is imminent