Cold Fronts

AVIATION WEATHER

CHAPTER THREE

or no turbulence. Precipitation from cumuliform clouds is showery and the clouds indicate

turbulence.

The slope is the ratio of the vertical rise to horizontal distance. The slope of a warm front is

generally shallow, while the slope of a cold front can be quite steep (Figure 3-10). Shallow

frontal slopes tend to produce extensive cloudiness with large areas of steady precipitation, while

steep frontal slopes tend to move rapidly producing narrow bands of cloudiness and showery

precipitation. Steep frontal slopes normally separate air masses of vastly different properties,

indicating the potential for more severe weather.

49 F

SLOPE 200 : 1

52 F

48 F

WARM

AIR MASS

51 F

MILE

54 F

COLD

57 F

AIR MASS

60 F

200 MILES

47 F

50 F

SLOPE 100 : 1

42 F

48 F

51 F

COLD

WARM

MILE

54 F

AIR MASS

57 F

60 F

100 MILES

Figure 3-10 Frontal Slope

The speed of the frontal movement affects the weather associated with it. A narrow band of

more severe weather generally accompanies faster moving fronts. On the other hand, slower

moving fronts have less severe weather, but the frontal zone is more extensive.

The greater the contrast in temperature and moisture between the colliding air masses, the greater

the possibility of weather associated with a front, particularly severe weather. For example, most

tornadoes occur in the spring due to very cold, dry air from Canada colliding with very warm,

moist air from the Gulf of Mexico.

308.

COLD FRONTS

A cold front is the leading edge of an advancing cold air mass. In this case, the colder (more

dense) air mass is overtaking and wedging underneath a relatively warmer (less dense) air mass.

As the cold air pushes the warm air upward, this motion sometimes produces very violent and

unstable conditions, to include strong thunderstorms (cumulonimbus clouds) and severe

turbulence. Figure 3-11 shows the manner in which a cold front is depicted on a surface weather

chart. Cold fronts move toward the SE at 20 knots, on average, and the wind shift is from the

SW to the NW.

Mechanics of Frontal Systems 3-11