Figure 3-4. Frontal Symbols

CHAPTER THREE

AVIATION WEATHER

them can be hundreds of miles long. Air masses and fronts are three-dimensional. The point

where a front comes in contact with the ground is called the surface front.

The surface front is the line plotted on surface analysis charts with different colors and shapes

representing each type of front, as pictured in Figure 3-4.

Type of Front

Color Scheme

SYMBOL

Cold front

Blue

Warm front

Red

Occluded front

Purple

Stationary front

Blue and Red

Trough

Brown or Black

Ridge

Yellow or Black

Squall line

Purple

Figure 3-4 Frontal Symbols

The frontal zone is the area encompasses the weather located on either side of the front. The

depth of this frontal zone depends on the properties of the two air masses. When the properties

differ greatly, the resulting narrow frontal zone can include sudden and severe weather changes.

It is often impossible to determine the exact outer boundaries of a frontal zone. Most active

weather is focused along and on either side of the surface front and frontal zone. Likewise, most

aviation weather hazards are also found in the vicinity of fronts. In the mid-latitudes, fronts

usually form between the warmer, tropical air to the south and the cooler, polar air to the north.

When a pilot passes through a front or a front moves past a station, the atmospheric conditions

change from one air mass to those of the other. Abrupt changes indicate the frontal zone is

narrow and in some cases, the zone can be less than a mile wide. On the other hand, gradual

changes indicate the frontal zone is broad and diffuse, often over 200 miles in width. Abrupt

changes will bring more severe weather than gradual changes.

Aviation weather hazards are not limited to the area of frontal zones. Some fronts do not

produce clouds or precipitation. Additionally, weather associated with one section of a front is

frequently different from the weather in other sections of the same front. Do not conclude all

3-4

Mechanics of Frontal Systems