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Rod Machado’s Private/Commercial Pilot Handbook
12-36

Cold Front Characteristics
A cold air mass overtaking a warm
air mass is called a cold front. Cold
air, being heavier than warm air,
moves along the surface, pushing
warmer air up in a bulldozer-type
action. Because of its consistency and
surface friction, the leading edge of
the cold air tends to stick to the sur-
face, forming a steeply sloped frontal
edge, as shown in Figure 61. Faster
moving cold fronts have steeper
frontal slopes than slower ones. Fig. 61
Frontal steepness is relative. To
me, a set of stairs leading up to a
children’s slide is steep. To a moun-
tain climbing friend, the face of
Yosemite’s El Capitan is steep (at
least that’s what he told me in the
hospital emergency room). Cold
frontal slopes range on a meteorologi-
cal scale of 1/50 (that’s steep) to
1/150 (not too steep) and average
about 1/80. A slope of 1/80 means
that 80 miles behind the point where In the Northern Hemisphere, not the environment that’s lifted, it’s
the cold front is at the surface, the strong cold fronts are usually orient- a parcel that’s somehow pushed
top of the cold air would be 1 mile ed in a northeast to southwest direc- upward. Cold fronts provide an excel-
above the ground (Figure 61). tion and move toward the east and lent means of lifting these parcels. Of
southeast, as shown in Figure 61. course, the longer and steeper the
Figure 61 shows a cross sectional
They are often followed by colder and front, the larger the number of
view of the cold front. The diagram is
drier weather. The cloudiness and parcels lifted. Therefore, the effects
exaggerated for clarity, since the cold weather associated with the front of stability or instability of the air are
air is nowhere near as tall, relative to
depends on the degree of stability more widespread.
its length in this picture. A more and moisture content of the air mass
realistic vertical versus horizontal ahead that’s being lifted by the front. Two Types of Cold Fronts
view of this front is shown at the bot- Cold fronts can be divided into two
tom of the diagram. With tops of cold Keeping It in Perspective general types: fast-moving and slow-
air ranging up to 25,000 feet, the cold Earlier we talked about how moving.
front occupies a relatively small ver- parcels of air are lifted within their Fast moving cold fronts have been
tical slice of the atmosphere. environment. Keep in mind that it’s
clocked in excess of 60 MPH, which
means you can be doing the legal
freeway speed limit in some states
Fig. 62
and get run over by a speeding cold
front. On average, they usually move
at half that speed. Their speed is gen-
erally faster in winter than in the
summer months.
Most of the cloudiness and precipi-
tation associated with a cold front is
located along and ahead of the area
where warm and cold air meet, as
shown in Figure 62. Because of the
cold front’s high speed, this weather
is often the most hazardous that
pilots encounter. Couple a fast mov-
ing, steep-sloped cold front with