Longwaves and
Shortwaves
Downwind
of LW trough is conducive
to cyclone development
(red shading) These are
large areas with modest-levels
of upper-level divergence!
One
longwave typically spans North
America (3). About 3-5 longwaves
are present on any given day.
They are move very little
from day to day.
Ahrens,
Meteorology Today, 5th Ed.