  BY GEORGE: On the Front  There's a lot of information that the
surface daily weather map contains, from high pressure areas and
low pressure areas, to all types of precipitation, and of
course, "fronts." Here, I'd like to take a closer look at what
all these fronts mean, and what kinds there are.  Starting with
the basic cold front, as depicted on a daily weather map by a
blue line with triangles along it, the cold front marks the
leading edge of a change of airmass. Now, it gets a little
complicated. The temperature behind a cold front is not
necessarily colder than the air ahead of the cold front.
Sometimes, temperatures may actually rise behind a cold front.
How can this be? Well, the truest definition of a front really
deals with a measure of air density behind and ahead of the
front. The air behind a cold front is always denser than the air
that it is replacing. Most often this is true in the case of
colder air replacing warmer air, as most of us have become
accustomed to when hearing about a cold fron