Weather Fronts

How cold fronts and warm fronts change the weather

How to explore

  1. Explore Cold Fronts, then Warm Fronts, then Compare and Predict.
  2. Press Play, or drag the Time slider yourself.
  3. Watch the person and read the weather report. Use your observations to answer three questions in each part.
Tip: the space bar plays and pauses.
Time Hour 0 of 6
Cold Front Warm air Cold air Cold front Rising warm air Cumulonimbus Nimbostratus Altostratus Cirrostratus Cirrus Virga: rain evaporating in dry air Front movement Hour 0 of 6

Weather report where the stick person is standing

Front status…
Sky…
Precipitation…
Temperature…
Wind…
Air pressure…

Simplified examples: Weather can vary from one front to another. Times, temperatures, and winds are examples, not forecasting rules. Cloud sizes and front slopes are exaggerated.

Learn more about the science
  • Air masses and fronts. An air mass is a large body of air with similar temperature and moisture. A front is the boundary between two different air masses.
  • Warm air rises at both fronts. At a cold front, advancing cold air pushes under warmer air and lifts it along a steeper slope. At a warm front, advancing warm air rises gradually over retreating cold air. Colder air is generally denser than warmer air at the same pressure.
  • Moist air can form clouds. Both examples contain moist air. As air rises, it expands and cools. If it cools enough, water vapor condenses into tiny liquid droplets that form clouds. Clouds can also contain ice crystals. Droplets can grow and fall as rain.
  • Compare the weather. In these examples, the cold front brings a brief period of heavier rain and cooler air. The warm front brings a longer period of steady rain, followed by warmer air. Not every front brings rain. Thunderstorms need moisture, lift, and air that can keep rising; they can also occur at warm fronts.

Sources: National Weather Service: Fronts · Thunderstorm ingredients · UCAR: Weather Fronts · NOAA: Weather Maps

Check for Understanding

Use the simulation as you answer. Check each set of three, then try again if needed.