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FRONTAL AND OROGRAPHIC CLOUDINESS AND PRECIPITATION
AIR MASS CLOUDINESS AND PRECIPITATION

Aerographers Mate 1 & C
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The perpendicular component of  the  upper  winds associated  with  the  inactive  cold  front  causes  the cloud  bands  to  appear  as  narrow,  fragmented,  or discontinuous.   The   band   of   clouds   is   comprised mainly  of  low-level  cumulus  and  stratiform  clouds, but  some  cirriform  may   be   present.   Occasionally, inactive  cold  fronts  over  water  will  have  the  same appearance as active fronts over land, while overland they  may  have  few  or  no  clouds  present.  Figure  4-6 depicts  the  fragmented  clouds  associated   with   an inactive cold front in the lower portion, while a more active  cold  front  cloud  presentation  is  shown  in  the upper portion. Warm Front As  with  cold  fronts,  the  use  of  constant  pressure charts   in   conjunction   with   the   surface   synoptic situation   is   helpful   in    forecasting    warm-frontal cloudiness and precipitation. Cloudiness and precipitation occur where the 700- hPa flow across the warm front is from the warm air to the cold air, and is moving in a cyclonic path or in a  straight  line.  This  implies  convergence  associated with    the    cyclonic    curvature.    Warm    fronts    are accompanied by no weather and few clouds if the 700- hPa  flow  above  them  is  anticyclonic.  This  is  due  to horizontal   divergence   associated   with   anticyclonic curvature. The 700-hPa ridge line ahead of a warm front may be   considered   the   forward   limit   of   the   prewarm frontal  cloudiness.  The  sharper  the  ridge  line,  the more accurate the rule. When  the  slope  of  the  warm  front  is  gentle  near the  surface  position,  and  is  steep  several  hundred miles   to   the   north,   the   area   of   precipitation   is situated in the region where the slope is steep. There may  be  no  precipitation  just  ahead  of  the  surface frontal position. Warm  fronts  are  difficult  to  locate  on  satellite imagery. An active warm front maybe associated with a  well  organized  cloud  band,  but  the  frontal  zone  is difficult to locate. An active warm front maybe placed somewhere   under   the   bulge   of   clouds   that   are associated  with  the  peak  of  the  warm  sector  of  a frontal   system.   The   clouds   are   a   combination   of stratiform    and    cumuliform    beneath    a    cirriform covering. See figure 4-7. You    must    remember    that    no    one    condition represents what could be called typical, as each front presents a different situation with respect  to  the  air masses   involved.   Therefore,   each   front   must   be treated    as    a    separate    case,    by    using    present indications, geographical location, stability of the air masses,  moisture  content,  and  intensity  of  the  front to determine its precipitation characteristics. Figure 4-6.-Inactive and active cold front satellite imagery. 4-5





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