JPATS Weather - NETC

JPATS AVIATION WEATHER BOOKLET
Figure 3-13 — Stationary Front
Stationary Fronts
Sometimes the frontal border between the air masses shows little or no movement. Since neither
air mass is replacing the other, the front is called a stationary front (Figure 3-13). Stationary
fronts are indicated on surface charts by an alternating warm and cold front symbols, retaining
their original red and blue colors, but pointing in opposite directions. Even though the front may
not be moving, winds can still be blowing. Surface winds tend to blow parallel on both sides of
the front rather than against and or away from it. Therefore, a stationary front has a 180° wind
shift. The wind shift may be from any one direction to the opposite direction, as stationary fronts
are less likely to be aligned in any one particular direction.
The weather conditions occurring with a stationary front are similar to those found with the
warm front, but are usually less intense. The weather pattern of a stationary front may persist in
one area for several days, until other, stronger weather systems are able to push the stationary
front weather along its way.
OCCLUDED FRONTS
Occluded fronts form when a faster moving cold front overtakes a slower moving warm front.
There are two types of occluded fronts, cold and warm. The type of occlusion that forms depends
on which front remains in contact with the ground. For example, if the cold front remains in
contact with the ground, then it is named a cold front occlusion.
Occlusions are shown on surface charts with both cold and warm frontal symbols pointing in the
same direction, but colored purple. Both types of occlusions tend to be aligned from NW to SE,
and hence move toward the NE at the speed of the front that remains on the ground. The wind
shift across either type of occlusion will be a 180° shift, as there are actually two fronts in the
same location. Therefore, ahead of the occlusion, the winds will be the same as those ahead of
the warm front, and behind the occlusion, the wind will be from the same direction as behind the
cold front: the wind shift is SE to NW. Because the occluded front is the result of the meeting of
3-14 Version 3.2/Dec 08