Classroom 9: Atmospheric pressure explained

Classroom 9

SIOUX CITY, Iowa (KCAU) – High pressure brings sunshine and low pressure brings rain.

Air pressure is the weight of air molecules pressing down on the earth. Typically we look at sea level pressure which is about 1,013 millibars. Millibars is a unit of measurement for pressure. There are a few types of units used for pressure, the main one we usually use is millibars.

The two types of pressure we deal with are high pressure and low pressure. High pressure and low pressure have different effects on our weather patterns.

To start with, high pressure is usually associated with calmer and nicer weather, like more sunshine in the area and minimal rain chances. High pressure can also be seen by the movement of wind. Wind moves from high pressure to low pressure.

This means winds will “spiral clockwise” out of the center of the high-pressure system. We see good weather with high-pressure systems because the air is forced down towards the surface, which causes evaporation and nicer weather in the area.

This is where low-pressure comes into play. As I mentioned, winds move from high pressure to low pressure. So if they spiral clockwise out of high pressure, then they will spiral counterclockwise into the low-pressure system.

To visualize this, think of a hurricane. A hurricane is a massive low-pressure system. Along with this, low-pressure systems typically bring inclement weather to the area, usually rain, snow, and/ or storms.

This happens because in a low-pressure system air is forced upwards into the atmosphere, which causes water vapor (water droplets) to condense, resulting in rain.

Low pressure can also cause some physical changes in our bodies, like headaches and other pain flares (such as arthritis or chronic pain).

So remember, if we are having nice, dry, and pleasant weather, we most likely have a high-pressure system in or near Siouxland.

But, if we have bad weather, like rain and or thunderstorms, we most likely have a low-pressure system in or near Siouxland.

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