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

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

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

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

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: 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

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

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

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