High Pressure, Low Pressure and Fronts

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HIGH AND LOW PRESSURE
SYSTEMS
WEATHER
SYSTEMS
UNIT
Regents Earth Science
By the end of this class, you will be able to:
*Compare and contrast high and low pressure
systems
*Identify areas of high and low pressure on a
weather map
DO NOW: What’s in a letter?
Take a moment to think about what each
letter stands for when used on a weather map
Compare/Contrast Chart
High and Low Pressure
High Pressure
Type of phenomenon
Determined by…
Moving inward on
isobars…
Density of air
Representation on a map
Motion of air
Also known as…
Motion of air causes a
zone of…
Stability of atmosphere
Low Pressure
Weather system
Changes in air pressure
Pressure Increases
Pressure Decreases
Higher
H (typically blue)
Clockwise, air sinks
Anticyclone
Divergence
Lower
L (typically red)
Counterclockwise, air
rises
Cyclone
Convergence
Stable
Unstable
High Pressure
LOW PRESSURE
Low vs. High
Thumbs up for high, Thumbs down for low
Identify one center of high pressure and one center of low
pressure using the letters on the map below. Be able to briefly
explain your answer.
FRONTS
Front: The leading edge of an air
mass-branch from low pressure
systems
Fronts are shown by
lines with symbols that
show the type of front
and the direction of
movement
Fronts- ESRT page 13
Warm front: an area
where a warm air mass
is replacing a cooler air
mass
What to Expect
Before the front:
A. cool or cold temps
B. falling barometer
C. increasing & thickening clouds
D. light-to-moderate precip
E. winds from the e-se,
F. Temp and dp get closer
together/higher humidity
 After the front:
A. Warmer and more humid weather
conditions
B. clearing clouds
C. a brief rise in pressure
D. winds from the s-sw
E. Temp and dp are close/high
humidity
 NOTE: “A high dewpoint” means that the
temperature and dewpoint are close
together. (ex. 32F temp, 30 F dewpoint)
 “A low dewpoint” means that the
temperature and dewpoint are far apart (ex.
55F temp, 30F dewpoint)
 There is ALWAYS a dewpoint!
Cold Front
Cold front: an area where
a cold air mass is
replacing a warmer air
mass
What to Expect
 Before the Front:
A. winds from the s-sw
B.
C.
D.
E.
F.
warm temps
a falling barometer (dropping
pressure)
an increase in clouds
a short period of precip
Temp/dp are close; high humidity
 After the Front:
winds from the w-nw
B. a drop in temps
C. a rise in pressure
D. showers followed by clearing
skies
E. Temp and DP get farther apart/
lower humidity
A.
Stationary Front
Stationary Fronts: a
boundary between air masses
that are not moving
What to expect: a
noticeable change in wind
direction or temperature
when crossing from one
side of the front to the
other
Occluded Fronts
Occluded Front: occur
when warm air is pushed
above Earth’s surface by
cooler air that is closing in
from both sides
DO NOT WRITE
 A developing cyclone usually has a
warm front and a faster moving cold
front that wraps around the storm.
 An occluded front forms when cold air
behind the cold front catches up to the
warm front, which is stuck behind the
cool air already in place
 What to expect: A change in temp.,
dewpoint or wind direction is possible
Occluded Front Development
 Phase 1:
 Phase 2
Animation of Fronts <3
 Animation of Fronts
Movement of Weather Revisited
Most of the tracks (paths)
follow a southwest to
northeast pattern because of
the United States’ location in
the prevailing southwest
wind belt
 Video: Tying it Together!: Jet Streams, Pressure
Systems and Fronts
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