If the warm air is conditionally unstable, the slope is shallow, and sufficient lifting occurs, the

Figure 4-6-1.Types of stable stationary fronts.

clouds are then cumuliform or stratiform with embedded towering cumulus. If the energy re-lease is great (warm, moist, unstable air), thunderstorms result.

Within the cold air mass, extensive fog and low ceiling may result if the cold air is saturated by warm rain or drizzle falling through it from the warm air mass above. If the temperature is below 0C, icing may occur; but generally it is light (view A of fig. 4-6-2). The shallow slope of an unstable stationary front results in a very broad and extensive area of showers, fog, and reduced visibility.

If the slope of an unstable stationary front is steep and sufficient warm air is advected up the slope or the front moves slowly toward the warm air mass, violent weather can result (view B of fig. 4-6-2). Heavy rain, severe thunderstorms, strong winds, and tornadoes are often associated with this front.

The width of the band of precipitation and low ceilings vary from 50 miles to about 200 miles, depending upon the slope of the front and the temperatures of the air masses. One of the most annoying characteristics of a stationary front is that it may greatly hamper and delay air opera-tions by persisting in the area for several days.

Figure 4-6-2.Types of unstable stationary fronts.

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