1. High and Low Pressure Systems Weather Systems Unit
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

2. Compare/Contrast Chart High and Low Pressure
High Pressure
Low Pressure
Type of phenomenon
Weather system
Determined by…
Changes in air pressure
Moving inward on isobars…
Pressure Increases
Pressure Decreases
Density of air
Higher
Lower
Representation on a map
H (typically blue)
L (typically red)
Motion of air
Clockwise, air sinks
Counterclockwise, air rises
Also known as…
Anticyclone
Cyclone
Motion of air causes a zone of…
Divergence
Convergence
Stability of atmosphere
Stable
Unstable

3. High Pressure

4. LOW PRESSURE

5. Low vs. High

6. Thumbs up for high, Thumbs down for low

7. 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.

8. FRONTS
Front: The leading edge of an air mass-branch from low pressure systems

10. Fronts are shown by lines with symbols that show the type of front and the direction of movement

11. Fronts- ESRT page 13
Warm front: an area where a warm air mass is replacing a cooler air mass

12. Before the front: What to Expect cool or cold temps falling barometer
increasing & thickening clouds
light-to-moderate precip
winds from the e-se,
Temp and dp get closer together/higher humidity

13. 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

14. 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!

18. Cold Front
Cold front: an area where a cold air mass is replacing a warmer air mass

19. What to Expect Before the Front: winds from the s-sw warm temps
a falling barometer (dropping pressure)
an increase in clouds
a short period of precip
Temp/dp are close; high humidity

20. After the Front:
winds from the w-nw
a drop in temps
a rise in pressure
showers followed by clearing skies
Temp and DP get farther apart/ lower humidity

24. Stationary Fronts: a boundary between air masses that are not moving

25. What to expect: a noticeable change in wind direction or temperature when crossing from one side of the front to the other

27. Occluded Fronts
Occluded Front: occur when warm air is pushed above Earth’s surface by cooler air that is closing in from both sides

28. 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

29. Occluded Front Development
Phase 1:
Phase 2

31. Animation of Fronts <3

32. 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