|FINDING THE L OR H|
BY SURFACE WIND DIRECTION
METEOROLOGIST JEFF HABY
Wind travels from high toward low pressure. However, the
Coriolis deflection and
the path of the wind so that it does not flow directly from high into low pressure. The wind still
flows from high toward low pressure but at an angle depending on how much friction is present. When
friction is stronger the wind travels more directly toward low pressure. Typically the wind will
travel at about an angle of 30 degrees toward lower pressure. This angle will be less over large
bodies of water since friction is less. In a case of strong wind over rough terrain the angle
will be greater than 30 degrees.
In a case with no friction, the wind will flow parallel to the pressure systems since the
pressure gradient and Coriolis will be in balance. On a sheet of paper, place of Low pressure
symbol on the left side of the piece of water and a High pressure symbol on the right side. Directly
between the pressure systems the wind will be flowing from the south (toward the top of the
piece of paper). Thus, with your back to the wind the low pressure system will be directly to the
left and the high pressure system directly to the right.
Since friction alters the wind direction by about 30 degrees, once your back is to the wind you
will need to rotate your body by 30 degrees to the right. Once you rotate your body 30 degrees
to the right then the low pressure system will be directly to the left and the high pressure
system directly to the right. Look at the placement of the pressure systems on a weather map and
compare that to where you determine the pressure systems to be by using the method described and
see how well it works.