MART Vol. II MO/MP - NESA - Civil Air Patrol

If a flight were made from Pittsburgh to St. Louis, ceiling and visibility woulddecrease steadily. Starting under bright skies, with unlimited ceilings andvisibilities, lowering stratus-type clouds would be noted as Columbus wasapproached, and soon afterward precipitation would be encountered. Afterarriving at Indianapolis, the ceilings would be too low for further flight.Precipitation would reduce visibilities to practically zero. Thus, it would be wise toremain in Indianapolis until the warm front had passed, which might require a dayor two.WARM AIRCirrostratusCirrusAltostratusNimbostratusCOLD AIRSt Louis Indianapolis Columbus PittsburghIf a return flight to Pittsburgh was made, it would be recommended to waituntil the front had passed beyond Pittsburgh, which might require three or fourdays. Warm fronts generally move at the rate of 10 to 25 miles an hour.On the trip from Pittsburgh to Indianapolis a gradual increase in temperaturewould have been noticed, and a much faster increase in dew point until the twocoincided. Also the atmospheric pressure would be gradually lessening becausethe warmer air aloft would have less weight than the colder air it was replacing.This condition illustrates the general principle that a falling barometer indicates theapproach of stormy weather.3.3.3 Cold FrontAs a cold front moves it functions like the blade of a snowplow, sliding underthe warmer air and forcing it aloft. This causes the warm air to cool suddenly andform cloud types that depend on the stability of the warm air.In fast-moving cold fronts, friction retards the front near the ground, whichbrings about a steeper frontal surface. This steep frontal surface results in anarrower band of weather concentrated along the forward edge of the front. If thewarm air is stable, an overcast sky may occur for some distance ahead of thefront, accompanied by general rain. If the warm air is conditionally unstable,scattered thunderstorms and showers may form in the warm air. At times analmost continuous line of thunderstorms may form along the front or ahead of it.These lines of thunderstorms (squall lines) contain some of the most turbulentweather experienced by pilots. Behind the fast-moving cold front there is usuallyrapid clearing, with gusty and turbulent surface winds, and colder temperatures.The slope of a cold front is much steeper than that of a warm front and theprogress is generally more rapid -usually from 20 to 35 miles per hour, although in51