Weather on a Front. Image by DiyMid.

Weather on a Front. Image by DiyMid.

ZIMSEC O Level Geography Notes: Fronts

Fronts

-A front is a boundary between two air masses. Fronts are classified and named according to which air mass is replacing the other.

Warm Front

A warm front: Image by ECN

A warm front: Image by ECN

Side view of a warm front. Image by Climateandweather.

Side view of a warm front. Image by Climateandweather.

  • Occurs when warm air is displacing cold air i.e cold air is receding.
  • The air behind a warm front is warm and moist, while the air ahead of a warm front is cooler and less moist.
  • Similar to the cold front, there will a shift in wind direction as the front passes and a change in pressure tendency.
  • Warm fronts have a more gentle slope than cold fronts, which often leads to a gradual rise of air.
  • This gradual rise of air favors the development of widespread, continuous precipitation, which often occurs along and ahead of the front.
  • 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 associated with a frontal inversion (warm air overrunning cooler air).
  • Warm fronts are represented on a weather map by a solid red line with semi-circles pointing in the direction of its movement as pictured above.

Cold Front

Cold Front. Image by ECN

Cold Front. Image by ECN

Side view of a cold front. Image by Oklahoma Climatological survey.

Another side view of a cold front. Image by ClimateandWeather

Another side view of a cold front. Image by ClimateandWeather

  • A front is called a cold front if the cold air mass is displacing the warm air mass.
  • The air behind a cold front is colder and typically drier than the air ahead of it, which is generally warm and moist.
  • There is typically a shift in wind direction as the front passes, along with a change in pressure tendency (pressure falls prior to the front arriving and rises after it passes).
  • 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.
  • Cold fronts usually bring cooler weather, clearing skies, and a sharp change in wind direction.
  • Cold fronts can be associated with squall lines.
  • Cold fronts have a steep slope, which causes air to be forced upward along its leading edge.
  • This is why there is sometimes a band of showers and/or thunderstorms that line up along the leading edge of the cold front.
  • Cold fronts are represented on a weather map by a solid blue line with triangles pointing in the direction of its movement as pictured above.

Occluded Front

Diagrams showing the formation of an occluded front:

Fast cold front catches up with a slow warm front to form an occluded front. Image by ECN

Fast cold front catches up with a slow warm front to form an occluded front. Image by ECN

The diagram shows a fast cold front catching up with a slow warm front to create an occluded front.

Occluded Front: Image by ECN

Occluded Front: Image by ECN

Side view of an occluded front. Image by CUNY.

Side view of an occluded front. Image by CUNY.

  • Generally, cold fronts move faster than warm fronts.
  • Sometimes in a storm system the cold front will “catch up” to the warm front.
  • An occluded front forms as the cold air behind the cold front meets the cold air ahead of the warm front.
  • Which ever air mass is the coldest undercuts the other.
  • The boundary between the two cold air masses is called an occluded front.
  • Occluded fronts are represented on weather maps by a solid purple line with alternating triangles and semi-circles, pointing in the direction of its movement as pictured above.
  • Occluded fronts are linked with areas of low pressure called depressions.

 

 


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