Weather App

" Understand what air pressure measures. This is the weight or pressure the air exerts on the ground and is measured in millibars. It is important to be able to read air pressure because pressure systems are associated with certain weather patterns. The average air pressure system measures 1013 mb (29.92 inches of mercury).[3] A typical strong high pressure system measures around 1030 mb (30.42 inches of mercury). A typical low pressure system measures around 1000 mb (29.54 inches of mercury. Image titled Read a Weather Map Step 6 2 Learn the air pressure symbols. To read air pressure on a surface analysis weather map, check for isobars (iso = equal, bar = pressure) – plain, curved lines that indicate areas of equal air pressure. Isobars play a major role in determining the speed and direction of wind.[4] When the isobars form concentric closed (but not always round) circles, the smallest circle in the center indicates a pressure center. This can be either a high-pressure system (depicted by an ""H"" in English, ""A"" in Spanish) or a low pressure system (depicted by an ""L"" in English, ""B"" in Spanish).[5] Air does not flow ""down"" pressure gradients; it flows ""around"" them due to the Coriolis effect (Earth spinning). Hence, wind direction is indicated by the isobars, counterclockwise around lows (cyclonic flow) and clockwise around highs (anticyclonic) in the northern hemisphere, thus creating wind. The closer the isobars are to one another, the stronger the winds. "