What kind of weather is associated with low pressure?
1 Answer
Explanation:
We also know that dry air has higher pressure than moist air. We know that warmer air has higher pressure than colder air given a constant volume. However since low pressure centers are not in a closed system like the atmosphere as a whole, volume does not stay constant. So what we usually see at a low pressure center is a humid air mass that is usually warm.
A humid air mass is going to give you more cloud, which is essential for weather. You do not get precipitation from clear skies, except in a very specific set of circumstances which I won't get into here. The other thing with a low pressure center is that it were low level convergence occurs (essentially air spirally into the low center). This convergence leads to upward motion of air which also drives more cloud and weather formation.
As far as winds go, it is true that there is a force pushing air from areas of high pressure to low pressure (pressure gradient force) however, since the Earth is spinning the air gets deflected and doesn't actually make it from high to low pressure. What ends up happening is the air flows perpendicular to the pressure gradient force so that (in the Northern Hemisphere) if you stand with your back to the wind, the low pressure will be on your left.
In the boundary layer (first 3000 ft AGL roughly) the friction of the Earth causes the air to slow down so that instead of it flowing perpendicular to the pressure gradient (as occurs above the boundary layer) the air slow spirals inward toward the low. This causes the low level convergence I talked about and the upward motion of air.
So with humidity, and with upward motion of air you have the necessary conditions for convective cloud to form. This is why low pressures give storms (thunderstorms in the summer, and snow storms in the winter).
