I forget the exact mechanism but in the middle lattitudes of the northern
hemisphere it generally begins with a small wave in the polar front which
detaches and begins to move east and south in the prevailing westerly
winds. In my recollection most of the lows in the US originate in or north
of the Aleutions. They then travel over southeast Alaska (which is why it
is so wet) in into the northwest. Once the low is formed, air moves inward
and then upward where it can be removed by the jet stream. It would seem
that lows would "fill in" quickly, but, since the winds follow the isobars
instead of heading directly for the low, it takes a long time. This is
obviously not a complete explanation of all lows and only what I recall from
reading weather texts..

Mike
MU-2


"Matt Whiting" wrote in message
...
Mike Rapoport wrote:

It is kinetic energy of each molecule that moves the the air. The
particles are just bouncing off other particles in a radom fashion. The
low pressure area has fewer molecules to run into (and bounce back
towards the higher pressure) so the molecules generally move towards the
low pressure. Thus it is the high pressure driving the air.

But how did you get all those molecules out of the area in order to form
the low? Conversely, how did you get all of the molecules together to
form the high?

Matt