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JPATS AVIATION WEATHER BOOKLET
Figure 3-11 — Warm Front
WARM FRONTS
A warm front is the boundary of the advancing warm air mass that is overtaking and replacing a
colder air mass. To do so, the warmer, less dense air must ride up and over the top of the cold air
mass. Figure 3-11 shows the manner in which a warm front is depicted on a surface weather
chart. The warm air mass gradually moves up over the frontal surface creating a broad area of
cloudiness. This cloud system extends from the front’s surface position to about 500 to 700 miles
in advance of it (Figure 3-12).
A warm front typically moves at a slower speed than a cold front–15 knots on average–and
produces a more gradual frontal slope, as well as sloping forward, ahead of the surface front.
Because of this slower speed and gradual slope, warm fronts are not as well defined as cold
fronts. The winds shift across a warm front from the SE to the SW.
Recognizing Warm Fronts During Flight
The most common cloud found along a warm front is the stratiform cloud. If one were to
approach the front from the east, the sequence of clouds would be cirrus, cirrostratus, altostratus,
nimbostratus, and stratus, rain and fog (Figure 3-12). Steady precipitation gradually increases
with the approach of this type of warm front and usually continues until the front passes.
3-12 Version 3.2/Dec 08