FOLLOWING A FRONTAL SYSTEM

KEY CONCEPTS

  1. Warm and cold air masses do not mix well. When they meet, they form a boundary or "front" between them.
  2. When a warm air mass is behind a cold air mass, the boundary is called a warm front, which approaches gradually with rainfall. Conversely, when a cold air mass is behind a warm one, the boundary is called a cold front, that acts like a wedge, forcing the warm air upward. Cold fronts typically move rapidly and bring heavy rains and winds.
 

MATERIALS

  • sample weather map (provided below)
  • current national weather maps collected over five days from a newspaper indicating frontal activity
  • map of the United States
 
 

PROCEDURE

  
 
 

Activity

  1. When a significant frontal system has been announced in weather reports, start collecting current weather maps or satellite images which indicate the front's direction of movement.
  2. Discuss the nature and classification of frontal systems. Also discuss the use of symbols to represent weather-related features.
  3. For the frontal system you and the students are following, discuss where the cold and/or warm air originated. What type of weather is found along the edge of the front as it moves along? Which direction is the front moving?
  4. Locate low-pressure areas on weather maps where the fronts meet. Is there a spiral movement of air (cyclone or anticyclone) and if so, what direction does the spiral move (clockwise or counterclockwise)?
  5. Once the direction of the front has been identified, try to forecast weather for points (cities) along its path.
  6. Compare student forecasts with actual weather data as it becomes available over a period several days.
 
 

Assessment Ideas

  • Students should record the passage of storm fronts using whatever equipment is available. The means by which a student can identify what has happened in the atmosphere and use data to document the event can be used as an assessment product.
 
 
 

CROSS-CURRICULAR IDEAS

  • Mathematics/ Technology: Have students use probes and computers or other equipment to chart various atmospheric conditions as a front passes. What happens to wind direction and speed, barometric pressure, temperature, relative humidity and cloud cover? Record and graph this data over several days and several fronts.
  • Art/Technology: Storms can very beautiful with striking images. Use time lapse photography and tape the passage of a front. Use the images to create scenes for use in cards or calendars. Store the images electronically to form a bank of such images.
  • Physics: Explain how lightning works. Record some time-lapse records of lightning strikes as a summer front passes .
 
 

VOCABULARY

  • anticyclone: a high-pressure system in which winds flow outward from the center, circulating clockwise in the Northern Hemisphere and counterclockwise in the Southern Hemisphere
  • cold front: the collision of air masses in which a cold air mass overtakes a warm one, forcing the warm air to rise and causing cumulus clouds to form.
  • cyclone: a low-pressure system in which winds spiral inward toward the center, circulating counterclockwise in the Northern Hemisphere and clockwise in the Southern Hemisphere. A hurricane is an example of a large warm tropical cyclone.
  • front: the bounary between air masses with different temperature and humidity characteristics.
  • warm front: the collision of air masses in which warmer, less dense air moves into an area of cold air over which it rises. Clouds forms in layers and rain may occur.
 
 

SOURCE

  • Adapted from "Winds of Change" educational CD-ROM, Copyright Caltech and NASA/Jet Propulsion Laboratory
  
  • isobar (dark blue, lower left): lines that connect points with the same barometric pressure reading. The black numbers -- 29.4, 29.7, 30.0, 30.3 -- show the barometric pressure value (in inches) at sea level.
  • high-pressure system (red "H," upper left): wind circulates clockwise around high-pressure systems in the northern hemisphere (opposite in the southern hemisphere)
  • high-pressure system (light blue "L," middle left): wind circulates counterclockwise around low-pressure systems in the northern hemisphere (opposite in the southern hemisphere)
  • cold front (green line with triangles, lower left): The triangles point in the direction toward which the cold front is moving.
  • warm front (brown line with semi-circles, middle left): The semicircles point in the direction toward which the warm front is moving.
  • stationary front (yellow circle around line with brown semicircles and green triangles, upper right): These are shown on weather maps as alternating triangles and semicircles.