Pressure and wind

Air has weight. The standard atmospheric pressure at sea level is about 1013 hPa. Warmer air is less dense, so it rises - leaving lower pressure behind. Higher-pressure air rushes in to fill the gap. That horizontal movement is wind.

On a weather map, lines connecting equal pressure are isobars. Tight isobars = fast winds. Lows (L) often bring storms; highs (H) bring fair weather.