JPATS Weather - NETC

JPATS AVIATION WEATHER BOOKLET
Figure 3-12 — Warm Front Cloud Formation
Warm Front Flight Problems
Wind Shift — Warm front wind shifts are not as sudden as those of a cold front, and therefore,
turbulence isn’t likely. The wind generally shifts from SE to SW.
Ceiling and Visibility — The widespread precipitation ahead of a warm front is often
accompanied by low stratus and fog. In this case, the precipitation raises the moisture content of
the cold air until saturation is reached. This produces low ceilings and poor visibility covering
thousands of square miles. Ceilings are often in the 300 to 900-foot range during steady, warm
frontal rain situations. Just before the warm front passes the station, ceilings and visibilities can
drop to zero with drizzle and fog. The worst conditions often occur in the winter when the
ground is cold and the air is warm; the best scenario for dense fog and low ceilings.
Turbulence and Thunderstorms — If the advancing warm air is moist an unstable, altocumulus
and cumulonimbus clouds can be embedded in the cloud masses normally accompanying the
warm front. These embedded thunderstorms are quite dangerous, because their presence is often
unknown to aircrews until encountered. Even with airborne radar, it can be difficult to
distinguish between the widespread areas of precipitation normally found with a warm front and
the severe showers from the embedded thunderstorms. The only turbulence along a warm front
would be found in such embedded thunderstorms. Otherwise, little to no turbulence exists in
warm front systems.
Precipitation and Icing — Approaching an active warm front from the cold air side (from the
east), precipitation will begin where the middle cloud deck is from 8000 to 12,000 feet AGL.
Often, this precipitation will not reach the ground–a phenomenon called virga. As you near the
front, precipitation gradually increases in intensity and becomes steadier. Occasional heavy
showers in the cold air beneath the frontal surface indicate that thunderstorms exist in the warm
air aloft. Drizzle, freezing drizzle, rain, freezing rain, ice pellets (sleet), and snow are all possible
in a warm front, depending on the temperature. The shallow slope and widespread thick
stratiform clouds lead to large areas of icing. It may take a long time to climb out of the icing
area, and you may need to descend into warmer air to avoid the icing.
Version 3.2/Dec 08 3-13