Wind is the motion of air. Air is a fluid (not a liquid) substance,
which means it flows. Things like temperature gradients (a change in temperature
over some distance) and pressure differences cause the air to flow. Nature likes
to even things out, and the motion of air results from this phenomenon.
Wind has really two components: the speed (or velocity), and the direction.
The direction in meteorology is the direction that the wind is coming from.
That is, if a wind is blowing from West to East, then it is a West wind. If
the wind is blowing from South to North, then that is a south wind. A weather
vane points to the direction the wind is coming from. There is a saying that
every wind has its weather. That is for sure a true statement. You will notice
in the Summer time that the winds here in mid-latitudes blow from the Southwest.
The southerly component usually means that warmer air from lower latitudes is
blowing (or being advected) in to our area. In the Winter, the winds have a
trajectory (or path) from the dark reaches of Canada. Being here in the Northern
Hemisphere in the mid-latitudes means that the wind blows from west to east.
Combine that with the knowledge that south winds usually bring warmer weather
and north winds bring colder weather, you can tell that the Summer months usually
have winds out of the southwest, and the Winter months are usually heralded
by winds from the northwest.
The energy from the Sun is really what drives the winds on our planet. The heat
energy drives something called the Jet Stream. The Jet Stream is a term used
to describe a high-altitude wind that blows in the upper levels of the atmosphere.
The winds in the Jet Stream in the Winter can blow at over 300 knots. This wind
energy is mixed down by convection and causes high velocity winds at the surface.
Except for a few orographic winds, the majority of the high winds on the surface
result in the energy aloft in the Jet Stream.
Please report any errors above to Max Riseman