Bob Dylan once wrote you don't need a Weatherman to tell which way the wind is blowing. But perhaps you do, at least to tell you what the atmospheric pressure is doing. Air pressure is one of the most important factors in determining what the weather is doing and what it will do. Atmospheric or barometric pressure is simply a measure of how hard the air above us is pushing down on earth. Meteorologists use measurements from across the country to find areas where the air is pushing down harder or less.
Low pressure tends to allow air to rise and leads to better chances of clouds and precipitation.