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WORLD AIR MASSES
Maritime Polar (mP) Air Pacific in Winter

Aerographers Mate, Module 05-Basic Meteorology
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shown in figure 4-5. In the mid-latitudes, for an air mass to  be  classified  as  arctic,  the  surface  temperature  is generally 0 degrees Fahrenheit (-18 degrees Celsius) or below. TRAJECTORY PATHS A AND B (CYCLONIC).—Paths A and B (fig. 4-5) are usually indicative of a strong outbreak of cold air and surface winds of 15 knots or more. This wind helps to decrease the stable conditions in the lower levels. If this modified air  moves  rapidly  over  rough  terrain,  the  turbulence results  in  low  stratocumulus  clouds  and  occasional snow flurries (see fig. 4-6). A  particularly  troublesome  situation  often  arises when  the  cold  air  flows  from  a  cold,  snow-covered surface   to   a   water   surface   and   then   over   a   cold, snow-covered  surface  again.  This  frequently  happens with air crossing the Great Lakes. (See fig. 4-7.) 4-8 110O 40O 110O G B A C D F E AG5f0405 Figure 4-5.—Trajectories of cP and cA air in winter. C P 20  TO   30   MPH TURBULENCE SNOW FLURRIES CLEAR  AND   COLD N S AG5f0406 Figure 4-6.—cP air moving southward. C P TEMP. DIFFERENCE  +  10    F O TEMP. 2000'    10    F O MOISTURE  AND WARM AIR  RISING O SURFACE  TEMP.  0    F NW SE WATER  TEMP.  34    F O SURFACE  TEMP.    21    F O CLEAR SNOW   FLURRIES APPALACHIAN MOUNTAINS 10    F O AG5f0407 Figure 4-7.—cP air moving over the Great Lakes (winter).







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