Fog!                                                           11/3

     1.  How does pressure change so drastically when a front passes and why is that pressure change in the same
         sense for both cold and warm fronts?
              Fronts form along the boundaries between different air masses.  In middle latitudes those fronts generally coincide
                  with southward advances and retreats of the polar front.  Because of upper level divergence along the polar front,
                  the surface pressure along that front is generally lower than the pressure to either side of it.  Whether the front is
                  moving so that the air on the colder side of it is displacing the air on the warmer side (cold front) or so that the air
                  on the warmer side is displacing air on the colder side (warm front), the lower pressure along the front, compared with
                  that to either side of it, causes the pressure to drop as the front approaches.  Often the pressure gradient near the front
                  is strong (the pressure changes much over a short distance) so as the front passes, the pressure at a fixed location
                  changes much over a short time period.   

    2.  Why do well-defined warm fronts rarely occur along the west coast and locally?
              Warm air masses approaching the west coast quickly modify to become colder because of the cold waters adjacent
                  to the coast.  As a result warm fronts quickly become poorly defined and dissipate.  Locally (and in any location
                  with deep mountain valleys) warm fronts do not readily displace cold dense air which becomes trapped in
                  deep valleys when warm air overrides it.

    3.  When a warm front occurs and the warm air rises above the colder air, does the front move the cold air
         mass, warm the cold air mass, or does it just stay above the cold air without displacing it?
              Over level or gently sloped terrain, the warm air mass simply displaces the cold air mass, creating a well-defined
                  warm front, even at the surface.  Locally, the warm air usually is unable to displace cold air in deep valleys.  It
                  simply stays above it, which creates an inversion and causes the front to lose its identity.  

    4.  What causes the widespread nature of the precipitation associated with warm fronts?
              Compared with cold fronts, the much more gently sloped frontal surfaces of warm fronts causes those frontal
                  boundaries, above the surface, to be spread over much greater areas.  Since precipitation tends to occur beneath
                  such boundaries, so also is the associated precipitation spread over a much greater area.

    5.  What circumstances lead to a cold versus a warm occlusion?
              The two interacting surface air masses along an occluded front usually both originated north of the polar front, but
                  over different areas so their characteristics, including temperature, are somewhat different.  Either can be colder,
                  and depending on whether that colder air mass is the one being displaced or the one doing the displacing, the
                  occlusion may be either warm or cold. 

    6.  What controls whether a frontal line is sharp or fuzzy?
              Frontal lines tend to be more sharply defined when the temperature difference on the two sides of the front is
                  greater.  Frontal lines tend to become fuzzy over irregular terrain.  Locally, frontal lines often are very poorly
                  defined, because the mountains tend to block the progress of a front.  Over plains and oceans, front lines are
                  often very sharp.

    7.  Why does the heaviest rainfall associated with an occluded front happen at the point of occlusion?
        Where does the condensation occur which produces that rainfall?
               Along an occluded front, northward from the point of occlusion, the point at which the three air masses meet is
                  progressively higher above the surface.  The condensation which produces precipitation occurs in that displaced,
                  elevated warm air mass.  Near the point of occlusion the lifting of the warm air has just begun and there is
                  relatively much water vapor there to be condensed out.  Progressing northward along the front, away from the point
                  of occlusion, there is less and less water vapor remaining to be condensed, so the precipitation intensity tends to
                  decrease.  Also since much of the energy driving a storm comes from the sinking of cold air and the rising of warm
                  air, there is maximum available energy at the point of occlusion, and progressively less as one moves away from
                  that point.