Regents Earth Science

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High and Low Pressure SystemsWeather 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
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DO NOW Whats in a letter? Take a moment to
think about what each letter stands for when used
on a weather map
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Compare/Contrast Chart High and Low Pressure
High Pressure Low Pressure
Type of phenomenon Weather system Weather system
Determined by Changes in air pressure 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

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High Pressure
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LOW PRESSURE
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Low vs. High
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Thumbs up for high, Thumbs down for low
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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.
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FRONTS

• Front The leading edge of an air mass-branch
  from low pressure systems

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

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Fronts- ESRT page 13

• Warm front an area where a warm air mass is
  replacing a cooler air mass

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What to Expect

• Before the front
• 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

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• 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

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• 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!

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Cold Front

• Cold front an area where a cold air mass is
  replacing a warmer air mass

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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

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• 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

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Stationary Front

• Stationary Fronts a boundary between air masses
  that are not moving

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

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Occluded Fronts

• Occluded Front occur when warm air is pushed
  above Earths surface by cooler air that is
  closing in from both sides

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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

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Occluded Front Development

• Phase 1

• Phase 2

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Animation of Fronts lt3

• Animation of Fronts

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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