JPATS Weather - NETC
JPATS Weather - NETC
JPATS Weather - NETC
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<strong>JPATS</strong> AVIATION WEATHER BOOKLET<br />
Winds<br />
Near the Earth’s surface, the wind changes direction across a front. In the Northern Hemisphere,<br />
as the front approaches and passes a station the wind changes direction in a clockwise rotation.<br />
When flying across a front, because of this wind shift you must adjust heading to the right to<br />
maintain your original ground track (Figure 3-6). This wind shift often creates a hazardous wind<br />
shear when departing or approaching an airfield. For example, winds at 220 degrees at 10 knots<br />
ahead of the front can rapidly change to 330 degrees at 20 knots gusting to 30 knots immediately<br />
after the front.<br />
Factors Influencing Frontal <strong>Weather</strong><br />
The weather along fronts is not always severe. Flying conditions can vary from insignificant<br />
weather to situations that are extremely hazardous. The hazardous situations can include<br />
thunderstorms, turbulence, icing, low ceilings, and poor visibility. The severity of the clouds and<br />
precipitation occurring along a front are dependent on the following factors:<br />
1. The amount of moisture available (shown by the dew point)<br />
2. The degree of stability of the lifted air<br />
3. The slope of the front<br />
4. The speed of the frontal movement<br />
5. The contrast in the amounts of temperature and moisture between the two air masses.<br />
The amount of moisture available, as indicated by the dew point, greatly determines the amount<br />
of weather associated with a front. Often little or no significant weather is associated with a front<br />
or a portion of a front because of a lack of moisture, despite the presence of all other factors.<br />
The degree of stability of the air that is lifted determines whether cloudiness will be<br />
predominantly stratiform or cumuliform. With stratiform clouds, there is usually steady<br />
precipitation and little or no turbulence. Precipitation from cumuliform clouds is showery and the<br />
clouds indicate turbulence.<br />
WARM<br />
AIR MASS<br />
SLOPE 200 : 1<br />
COLD<br />
AIR MASS<br />
200 MILES<br />
49° F<br />
52° F<br />
48° F<br />
51° F<br />
54° F<br />
57° F<br />
60° F<br />
1<br />
MILE<br />
47° F<br />
1<br />
MILE<br />
50° F<br />
42° F<br />
48° F<br />
51° F<br />
54° F<br />
57° F<br />
60° F<br />
SLOPE 100 : 1<br />
COLD<br />
AIR MASS<br />
WARM<br />
AIR MASS<br />
100 MILES<br />
Figure 3-7 — Frontal Slope<br />
3-8 Version 3.2/Dec 08
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