Sharp change in wind direction

Fronts are actually zones of transition, but sometimes the transition zone, called a frontal zone, can be quite sharp.

There are four types of fronts that will be described below: cold front, warm front, stationary front, and occluded front.

• sharp temperature changes over relatively short distances,
• changes in the moisture content of the air (dew point),
• shifts in wind direction,
• low pressure troughs and pressure changes, and
• clouds and precipitation patterns.

Figure 2 - Side View of a Typical Cold Front

Cold Fronts

• Cold front- a front in which cold air is replacing warm air at the surface.

• Some of the characteristics of cold fronts include the following:
  • The slope of a typical cold front is 1:100 (vertical to horizontal).
  • Cold fronts tend to move faster than all other types of fronts.
  • Cold fronts tend to be associated with the most violent weather among all types of fronts.
  • Cold fronts tend to move the farthest while maintaining their intensity.
  • Cold fronts tend to be associated with cirrus well ahead of the front, strong thunderstorms along and ahead of the front, and a broad area of clouds immediately behind the front (although fast moving fronts may be mostly clear behind the front).
  • Cold fronts can be associated with squall lines (a line of strong thunderstorms parallel to and ahead of the front).
  • Cold fronts almost always are easier to locate on a weather map than are warm fronts, primarily because of the strength of the high pressure system to the north and west of the cold front compared to that north of a warm front.
  • Cold fronts usually bring cooler weather, clearing skies, and a sharp change in wind direction.

  Figure 3 - Side View of a Typical Warm Front

  Warm Fronts

  • Warm front- a front in which warm air replaces cooler air at the surface.
  • Some of the characteristics of warm fronts include the following:
    • The slope of a typical warm front is 1:200 (more gentle than cold fronts).
    • Warm fronts tend to move slowly.
    • Warm fronts are typically less violent than cold fronts.
    • Although they can trigger thunderstorms, warm fronts are more likely to be associated with large regions of gentle ascent (stratiform clouds and light to moderate continuous rain).
    • Warm fronts are usually preceded by cirrus first (1000 km ahead), then altostratus or altocumulus (500 km ahead), then stratus and possibly fog.
    • Behind the warm front, skies are relatively clear (but change gradually).
    • Warm fronts are associated with a frontal inversion (warm air overrunning cooler air).
    Clouds and precipitation are quite prevalent to the north of the warm front.

    This results from the fact that low-level southerly winds in the "warm sector" of the cyclone rise up and over the cooler, more dense air at the surface located north of the warm front. The lifting leads to saturation, cloud formation, and, ultimately, to some form of precipitation.

    • In Oklahoma, warm fronts are rare in the winter and non-existent in the summer.

    Stationary Fronts

    • Stationary front- a front that does not move or barely moves.
    • Stationary fronts behave like warm fronts, but are more quiescent.
    • Many times the winds on both sides of a stationary front are parallel to the front.
    • Typically stationary fronts form when polar air masses are modified significantly so as to lose their character (e.g., cold fronts which stall).

    Figure 4 - Development of an Occluded Front

    Occluded Fronts

    Because cold fronts move faster than warm fronts, they can catch up to and overtake their related warm front. When they do, an occluded front is formed.