WEATHER (WX)


Probably the most important consideration regarding the atmosphere is weather. Weather is directly linked to the atmospheric temperature and pressure and is yet to be fully under stood. The following covers some of the more important aviation aspects of weather. This section will help you understand the complexity of weather patterns; and better equip you to understand how weather can affect your aircraft.


Weather is a result of the masses of air that are constantly in motion about our planet reacting with each other. These air masses are similar to the waters of the oceans, which are constantly in motion. The air masses (the ocean of air) are constantly heated by the sun, and this non-uniform heating causes the constant movement of air.


Air Masses The ocean of air is composed of large areas of air which have similar characteristics and ac quire the characteristics of the region in which they form: the coldness of the polar region, the heat and humidity of the tropics, the moisture of the oceans, and the dryness of the con tinents. Air masses are designated “maritime” when they form over water, and “continental” when they form over land.


As these air masses move, as a result of the circulation of the atmosphere caused by the sun’s heating and the flow caused by highs and lows, their characteristics are modified by the type of area they move into. This modification and constantly changing characteristics causes the phenomena we call weather.


A cP mP


Note standard air mass abbreviations: arctic (A), continental polar (cP), maritime polar (mP), continental tropical (cT), and maritime tropical (mT).


mP mT mT cT mT


Figure 11-24. North American air mass source regions.


Fronts As the air masses move, they are designated either as warm or cold, depending on whether the surface temperature of the area they are moving into is colder or warmer. During this movement, they absorb the temperature and moisture (humidity) of the regions they pass over and become less stable. When two air masses meet, they do not readily mix, rather they form a transition area much like boundaries. These boundaries between air masses are called fronts. If the mass of air is warmer than the mass it is moving into, the boundary is called a “warm front.” If the mass of air is colder than the mass it is en croaching upon, then the boundary is called a “cold front.”


WARM AIR


A cold front moves in and under the warm air, which produces a rapidly cooling air mass. The result is a violent change in weather conditions in a relevantly short span of time. Normally, good ceilings and visibility prevail, but, because of the violent nature of the cold front, stormy weather can form. Cold fronts can quickly produce nimbo-stratus and/or cumulo-nimbus clouds, heavy precipitation, gusty winds, turbulence and thunderstorms.


In a warm front, the lighter, warmer air has a tendency to slide up over the colder air it is meeting. If the warmer air has a high moisture content, as it rises it cools, condensation forms and normally pro duces rain or drizzle, stratiform-form clouds, low overcast condi tions or fog. Generally, the air is smooth with little turbulence.


CUMULONIMBUS


St. Louis 1008 1005 1005 1008 1011 1011 46


10 33


10 St. Louis


066 42


74 3


71 10 Indianapolis


071 4


METAR KSTL SCT010


77 6


73


102 8


25 Columbus


75 3


70


122 12


Pittsburgh 35 1014


METAR KCMH 1950Z BKN025


METAR KPIT 1011NIMBOSTRATUS 1011 SCT035 1014 1950Z


20012KT 6SM 25/24


COLD AIR Figure 11-27. Cold front cross-section with surface weather chart depiction and associated METAR. St. Louis 999 1002 1005 1008 1011


Indianapolis 200 miles


1014 1017


The movement of a warm front versus a cold front is amazing. The warm front moves slowly and may take days to pass. The cold front can pass rapidly in a matter of hours. This rapid movement adds to its storm producing capability. Adverse weather conditions are normally associated with low pressure areas and the fronts generated from their air mass movement.


999


65 1


65 1002


020 10


10 St. Louis Indianapolis


59 3


59 20


068 40


56 6


50


125 26


60 Columbus


53 10 34


166 18


Pittsburgh METAR KIND BKN020


METAR KCMH 1950Z 0VC060


1005 1008 1011 1014 1017 9 Aviation Basics Figure 11-26. Warm front cross-section with surface weather chart depiction and associated METAR. METAR KPIT SCT150 1950Z 1950Z


16012KT 3SM 15/15


13018KT 6SM 14/10


RA A2973 HZ A2990


13012KT 10SM 12/01


A3002 METAR KSTL 0VC010 1950Z


21018KT 1SM 18/18


–RA A2960


Columbus 400 miles


Pittsburgh 600 miles


20012KT 3SM 24/22


HZ A2983 FU A2989 METAR KIND ALTOSTRATUS OVC010 1950Z


CIRROSTRATUS 1950Z


30018KT 10SM 08/02


20024KT 3SM 24/23


CIRRUS A2979 +TSRA A2974


Indianapolis 200 miles


Columbus 400 miles


Pittsburgh 600 miles


COL


D


RI A


WARM AIR


WARM FRONT


COLD FRONT


Page 1  |  Page 2  |  Page 3  |  Page 4  |  Page 5  |  Page 6  |  Page 7  |  Page 8  |  Page 9  |  Page 10  |  Page 11  |  Page 12  |  Page 13  |  Page 14  |  Page 15  |  Page 16  |  Page 17  |  Page 18  |  Page 19  |  Page 20  |  Page 21  |  Page 22  |  Page 23  |  Page 24  |  Page 25  |  Page 26  |  Page 27  |  Page 28  |  Page 29  |  Page 30  |  Page 31  |  Page 32  |  Page 33  |  Page 34  |  Page 35  |  Page 36  |  Page 37  |  Page 38  |  Page 39  |  Page 40  |  Page 41  |  Page 42  |  Page 43  |  Page 44