Hobbies And Interests
Barometric Pressure Values
The average barometric pressure at sea level is 29.92 inches of mercury, which is equal to 1013.25 mb. The barometric pressure decreases by about 3.6 percent for every 1000 feet of elevation, but pressures measured at higher elevations are always corrected to a sea level value when reported. This allows meteorologists to compare pressure on a mountaintop to that in a deep canyon as if they were at the same elevation.
High and Low Pressure Cells
Meteorologists predict weather in part based on the difference in pressure between two locations. Relatively low pressure often indicates wet, rainy weather or even storms, while high pressure often means fair weather. Air moves from points of high pressure to points of low pressure, causing wind.
High and Low Pressure Cells on Weather Maps
Weather maps include isobars, contour lines that connect points with the same barometric pressure. High and low pressure cells appear as circular or oval patterns of isobars, often marked with a bold H or L, respectively. On some maps, the highest and lowest measured values also are posted.
Measured Pressure Extremes
The highest barometric pressure ever recorded is 1083.3 mb, in the vicinity of a persistent high over Siberia. The lowest is 870 mb, at the eye of a Pacific typhoon. This means that a high on a weather map with a measured maximum of 1080 mb is an area of very high, near-record high pressure.