Regents Earth Science

HIGH AND LOW PRESSURE SYSTEMSWEATHER 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

DO NOW: What’s in a letter?

Take a moment to think about what each letter stands for when used on a weather map

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 (increases) Lower (decreases)

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

Typical weather Clear skyDry

Stormy

Compare/Contrast ChartHigh and Low Pressure

High Pressure

LOW PRESSURE

Low vs. High

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-

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

What to Expect

Before the front passes: cool or cold temperatures, a falling barometer, an increase and thickening in clouds, light-to-moderate precipitation, winds from the south-southeast, rise in dewpoint

After the front has passed: Warmer and more humid weather conditions, clearing clouds, a brief rise in pressure, winds from the south-southwest, high dewpoint

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: winds from the south-southwest, warm temperatures, a falling barometer (dropping pressure), an increase in clouds, a short period of precipitation and a high dew point

After the Front: winds from the west-northwest, a drop in temps, a rise in pressure, showers followed by clearing skies, and a falling dewpoint

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

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 DevelopmentPhase 1: Phase 2

Animation of Fronts <3Animation 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