Geocentric Science

A falling barometer is the first sign. A barometer is an instrument used to measure atmospheric pressure. Typically high pressure is associated with cool, dry air and low pressure is associated with warm, moist air. Water vapor weighs less than air, therefore the more water vapor present, the lower the pressure. A falling barometer indicates that water vapor is approaching (wet weather).

In addition, other common signs of an approaching storm include increasing cloud coverage, increasing intensity of the wind, and falling temperatures.