JPATS Weather - NETC

JPATS AVIATION WEATHER BOOKLET
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 3-3).
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
tropopause.
Figure 3-3 — 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
fronts move faster than warm fronts, in general. Next, we usually see a 90° wind shift from one
side of the front to the other, with two exceptions that will be explained below. Finally, every
front is located in a trough of low pressure.
Version 3.2/Dec 08 3-5