Normal barometric pressure is typically around 101.325 kPa / 1013.25 mbar / 760 mmHg / 29/921 inHg. Pressure rarely increases or decreases more than 1 inch of mercury (3.386 kPa / 33.86 mbar / 25mmHg) above or below the 30-inch mark unless the weather conditions are extreme.
The highest ever recorded pressure on Earth was on December 31, 1968, at Agata Lake in Siberia, Russia when the weather conditions were clear and extremely cold at minus 50.8 degrees Fahrenheit. The recorded pressure was 108.38kPa / 1083.8 mbar / 812.92 mmHg / 32.01 inHg.
Many people suffer from migraines and headaches that are associated with rising and falling barometric pressures. Low air pressure means that there is less weight pushing down and the air is rising and cooling, which means that there are clouds forming. High air pressures means that there is more weight pushing down and so the air is sinking, which leads to less humidity and a warmer temperature. Falling barometric pressure is usually associated with either thunder in hot weather, wet weather, windy conditions or some kind of precipitation. Rising barometric pressure is usually associated with fairer weather and typically indicates that there will not be any storms that day. Clear skies are also associated with high barometric pressure.