The most common value-added analyses on surface maps are isobars, pressure systems, and boundaries. We’re used to seeing a blue H over a high-pressure center and a red L over a low-pressure system.

Question: What are constant pressure charts? Answer: Constant pressure charts like the 500 mb chart shown below may seem obvious to interpret. It has many features similar to what you might see on ...

But high in the atmosphere are vertical movements of air, which dictate the weather conditions we see at the surface. These vertical movements of air are what cause high or low pressure.