Weather question (highs and lows)

[E_Dawg]

OK so we have to study the highs and lows for flying... what to expect from each and how to deal with it (i.e. tail winds north of a high going east; stronger southerly winds south and / or west of a low = worse weather due to stronger low than forecast).

But what causes the pressure systems in the first place?

[EatSleepFly]

Unequal heating causes differences in pressure, which in turn, create pressure systems. A high is an area of high pressure, surrounded on all sides by lower pressure...and vice versa. Terrain type, geographic location, and atmospheric conditions are a few of the ways the earth heats unequally. I'd love to give you more details, but meteorology isn't my cup of tea. Anyone else?

[sbav8r]

I will just try to add to that.
A low, or depression, in the northern hemisphere will be associated with counterclockwise (cyclonic) winds converging on the center that increase in strength as the isobars get closer together on a weather map. As a pilot, you would experience constant right drift while approaching the center of a low and then a constant left drift when heading out of a low-pressure area. In addition, low-pressure areas are more intense than highs and are associated with unstable rising air. Therefore, one can expect the possibility of clouds due to the rising air at the center cooling. The instability in that rising air may lead to the formation of clouds with extensive vertical development accompanied by rain showers.
Highs on the other hand tend to be a more gradual pressure gradient with clockwise (anticyclone) winds in the northern hemisphere moving in an outward direction.

With that I will pass to someone else.

[Mavmb]

Just remember high pressure is good and low pressure is bad! High pressure means that the air is pushing harder towards the surface of the Earth. So that means that all the moisture will get pushed down to the surface of the Earth as well, generally resulting in clear skies. With low pressure, the air is exerting very little push onto the surface so all of that moisture rises up into the atmosphere causing clouds, rain, etc.