General Frontal Structure
The characteristics of each air mass on either side of the front diminish with increasing altitude.
At some level above the surface, usually above 15,000 to 20,000 feet, the differences between
the two air masses forming the front become negligible and the cloud and precipitation patterns
in the upper frontal zone are not easily attributable to one frontal type or another (Figure 3-6).
Therefore, the most significant frontal weather occurs in the lower layers of the atmosphere.
However, the temperature contrast between the air masses can sometimes extend as high as the
Figure 3-6 Frontal Zone Structure
Most fronts, regardless of type, have some common characteristics. First, fronts are named
according to the temperature change they bring. For example, if the temperature will become
warmer after the front passes, it is named a warm front. Second, fronts move across the country
with their attached low-pressure system and isobars, as the corresponding air masses move. As
they move, we are only concerned with any movement perpendicular to the line representing the
front; thus, fronts are considered to move perpendicular to the way they are drawn. Also, cold
Mechanics of Frontal Systems 3-7