The weather map fails to indicate what shifts of direction and changes
in velocity are likely to occur. The forecaster tries to anticipate
these, but he bases his conclusions chiefly upon an expected movement of
the low area; using the accumulated records of the paths of past storms.
But each storm is in reality a law unto itself; and while we know
something of the relations between pressure and flow of the air; as yet
we know very little about the relations of wind and weather. The problem
is complicated by the behavior of the load of water vapor.
[Illustration: FIG. 5. EUROS--THE SOUTHEAST WIND]
The Chief Forecaster of one of the great national weather services
recently wrote:
"Despite the fact that maps have now been drawn day by day for over
half a century, we may safely say that no two maps have been
identical."
It is perhaps unfortunate that so much attention has been given to the
cyclone or depression or LOW, and comparatively little to the HIGH or
anticyclone. For we are now beginning to understand that while there may
seem at first to be nothing specially noteworthy about a mass of air
where the pressure varies from 1020 to 1040 kilobars, that is, 2 to 4
per cent _above_ a standard atmosphere, with isobars irregularly curved
and feeble surface winds, yet the anticyclone is more important than the
cyclone in determining weather sequence; for the progressive motion of
the cyclone depends largely upon the strength of the anticyclone.