Another factor in Low Pressure - Rising Air
We've looked at many examples that cause air to rise and fall. A change in temperature or wind will cause air to rise. When an air mass is rising over a location the pressure will drop and the barometer will show a lower value. In this instance the barometer acts sort of like a scale. The rising movement of air takes some of the weight off the scale. In reality the air doesn't weigh any less, it just exerts less force downward, which results in less pressure. Look at the following image.

Note, the column of red liquid is lower on the barometer within the rising air. This is because rising air will create less pressure on the barometer. Rising air within the low-pressure system is able to form precipitation as explained in Lesson 10: Precipitation.

Wind flows counter-clockwise around a low-pressure weather system.
The Coriolis Effect works on low-pressure weather systems just as it does with high pressure. Remember that wind will be pulled from high pressure to low-pressure. The Coriolis Effect will make this wind turn to the right in the Northern Hemisphere. This is shown in the graphic to the left. For the Midwest this means that on the eastern side of the low-pressure center, the wind will be out of the south. This south wind is coming from a warmer area and gains moisture from the Gulf of Mexico.

On the west side of the low-pressure center the wind is coming from the north. This air will be cooler and does not have as much moisture as the south wind from the Gulf of Mexico. Notice the circulation of this low-pressure center will influence the movement of air masses and the characteristics of those air masses.