AEROGRAPHER'S MATE 3 & 2 





WARM AIR 





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COLD AIR // 





COLDER AIR 







WARM TYPE OCCLUSION 



201.58.1 

 Figure 14-13.— Vertical cross section of a warm 

 type occlusion. 



COLD TYPE OCCLUSION 



201.58.2 

 Figure 14-14.— Vertical cross section of a cold 

 type occlusion. 



The primary difference between a warm type 

 and cold type occlusion is the location of the 

 associated upper front in relation to the surface 

 front. (See fig. 14-15.) In a warm type occlusion 

 the upper cold front precedes the surface 

 occluded front by as much as 200 miles. In 

 the cold type occlusion the upper warm front 

 follows the surface occluded front by 20 to 

 50 miles. 



Since the occluded front is a combination of 

 a cold front and a warm front, the resulting 

 weather is that of the cold front's narrow band 



of violent weather and the warm front's wide- 

 spread area of cloudiness and precipitation 

 occurring in combination along the occluded 

 front. The most violent weather occurs at the 

 tip of the occlusion. (The tip is the point at 

 which the cold front is overtaking the warm 

 front.) 



Stationary Fronts 



When a front is stationary, the cold air 

 mass, as a whole, does not move either toward 

 or away from the front. In terms of wind 

 direction, this means that the wind above the 

 friction layer blows neither toward nor away 

 from the front, but parallel to it. It follows 

 that the isobars, too, are nearly parallel to a 

 stationary front. This characteristic makes it 

 easy to recognize a stationary front on a 

 weather map. 



The frictional inflow of warm air toward 

 a stationary front causes a slow upglide of 

 air on the frontal surface. As the air is lifted 

 to and beyond its lifting condensation level, 

 clouds form in the warm air above the front. 



If the warm air in a stationary front is 

 stable, the clouds are stratiform. Drizzle may 

 then fall; and as the air is lifted beyond the 

 freezing level, icing conditions develop and 

 light rain or snow may fall. At very high levels, 

 above the front, ice clouds are present. (See 

 fig. 14-16.) 



If the warm air is conditionally unstable 

 and sufficient lifting occurs, the clouds are 

 then cumuliform or stratiform with cumuliform 

 protuberances. If the energy release is great 

 (warm, moist, unstable air), thunderstorms 

 result. Rainfall is generally showery. 



Within the cold air mass extensive fog and 

 low ceiling may result, where the cold air 

 is saturated by warm rain or drizzle falling 

 through it from the warm air mass above. 

 If the temperature is below 0° C, icing may 

 occur, but generally it is light. (See fig. 14-17.) 



The width of the band of precipitation and 

 low ce* ig varies 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 operations by persisting in the 

 area for several days. 



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