METEOROLOGY FOR EVERYONE

Prepared by: Dr. Ahmet KILIÇ

FRONTS

 
COLD FRONT A front is defined as the transition zone between two air masses of different density. Fronts extend not only in the horizontal direction, but in the vertical as well. Therefore, when referring to the frontal surface (or frontal zone), we referring to both the horizontal and vertical components of the front.
WARM FRONT
STATIONARY FRONT
OCCLUDED FRONT

 

 

 

COLD FRONT

A cold front is defined as the transition zone where a cold air mass is replacing a warmer air mass. Cold fronts generally move from northwest to southeast. The air behind a cold front is noticeably colder and drier than the air ahead of it. When a cold front passes through, temperatures can drop more than 15 degrees within the first hour.

Lifting the warm moist air ahead of it
Precipitation Along a Cold Front . It is seen below is a sequence of vertical cross sections that depict the development of precipitation ahead of and along a cold front. The surging blue mass represents colder air behind the cold front (solid blue line) while the yellow shading indicates the warm moist air mass ahead of the front.
As the front advances, the colder air lifts the warmer air ahead of it (red arrows). The air cools as it rises and the moisture condenses to produce clouds and precipitation ahead of and along the cold front. In contrast to lifting along a wrm front, upward motions along a cold front are typically more vigorous, producing deeper clouds and more intense bands of showers and thunderstorms. However, these bands are typically quite narrow and move rapidly just ahead of the cold front.

 

 

 

 

WARM FRONT

 

A warm front is defined as the transition zone where a warm air mass is replacing a cold air mass. Warm fronts generally move from southwest to northeast and the air behind a warm front is warmer and more moist than the air ahead of it. When a warm front passes through, the air becomes noticeably warmer and more humid than it was before.

Warm moist air overriding colder air

Precipitation along a warm front . It is seen below is a sequence of vertical cross sections depicting the development of precipitation ahead of and along a warm front. The region shaded in blue represents a colder air mass while the yellow shading indicates the warm moist air behind the warm front (solid red line).

The frontal zone slopes up and over the colder air mass ahead of it. Warm air rides along the front (up and over the cold air mass), cooling as it rises, producing clouds and precipitation in advance of the surface warm front. Because the lifting is very gradual and steady, generally wide spread and light intensity precipitation develops ahead of a warm front.

 

 

STATIONARY FRONT

 

A front that is not moving. When a warm or cold front stops moving, it becomes a stationary front. Once this boundary resumes its forward motion, it once again becomes a warm front or cold front. A stationary front is represented by alternating blue and red lines with blue triangles pointing towards the warmer air and red semicircles pointing towards the colder air.

 

OCCLUDED FRONT

 

Occluded front forms when a cold front overtakes a warm front . A developing cyclone typically has a preceding warm front (the leading edge of a warm moist air mass) and a faster moving cold front (the leading edge of a colder drier air mass wrapping around the storm). North of the warm front is a mass of cooler air that was in place before the storm even entered the region.

 

As the storm intensifies, the cold front rotates around the storm and catches the warm front. This forms an occluded front, which is the boundary that separates the new cold air mass (to the west) from the older cool air mass already in place north of the warm front. Symbolically, an occluded front is represented by a solid line with alternating triangles and circles pointing the direction the front is moving. On colored weather maps, an occluded front is drawn with a solid purple line.

Changes in temperature, dew point temperature, and wind direction can occur with the passage of an occluded front. In the map below, temperatures ahead (east of) the front were reported in the low 40's while temperatures behind (west of) the front were in the 20's and 30's. The lower dew point temperatures behind the front indicate the presence of drier air.