The perpendicular component of the upper winds
associated with the inactive cold front causes the
cloud bands to appear as narrow, fragmented, or
discontinuous. The band of clouds is comprised
mainly of low-level cumulus and stratiform clouds,
but some cirriform may be present. Occasionally,
inactive cold fronts over water will have the same
appearance as active fronts over land, while overland
they may have few or no clouds present. Figure 4-6
depicts the fragmented clouds associated with an
inactive cold front in the lower portion, while a more
active cold front cloud presentation is shown in the
upper portion.
Warm Front
As with cold fronts, the use of constant pressure
charts in conjunction with the surface synoptic
situation is helpful in forecasting warm-frontal
cloudiness and precipitation.
Cloudiness and precipitation occur where the 700-
hPa flow across the warm front is from the warm air
to the cold air, and is moving in a cyclonic path or in
a straight line. This implies convergence associated
with the cyclonic curvature. Warm fronts are
accompanied by no weather and few clouds if the 700-
hPa flow above them is anticyclonic. This is due to
horizontal divergence associated with anticyclonic
curvature.
The 700-hPa ridge line ahead of a warm front may
be considered the forward limit of the prewarm
frontal cloudiness. The sharper the ridge line, the
more accurate the rule.
When the slope of the warm front is gentle near
the surface position, and is steep several hundred
miles to the north, the area of precipitation is
situated in the region where the slope is steep. There
may be no precipitation just ahead of the surface
frontal position.
Warm fronts are difficult to locate on satellite
imagery. An active warm front maybe associated with
a well organized cloud band, but the frontal zone is
difficult to locate. An active warm front maybe placed
somewhere under the bulge of clouds that are
associated with the peak of the warm sector of a
frontal system. The clouds are a combination of
stratiform and cumuliform beneath a cirriform
covering. See figure 4-7.
You must remember that no one condition
represents what could be called typical, as each front
presents a different situation with respect to the air
masses involved. Therefore, each front must be
treated as a separate case, by using present
indications, geographical location, stability of the air
masses, moisture content, and intensity of the front
to determine its precipitation characteristics.
Figure 4-6.-Inactive and active cold front satellite imagery.
4-5
