Glossary

Sea Level Pressure

Credit
Gavin Lang

Elevations and temperatures of weather stations A (at sea level), B (at 1,000m above sea level), and C (at 1,800m above sea level) are shown. The calculations below convert each station’s pressure reading to the corrected sea level value. The mathematics take into consideration station altitude, station temperature, and minor instrumentation corrections. In this example, we can now compare each station’s sea level pressure—higher pressure exists inland (right side of diagram) and lower pressure exists near the water (left).

Sea level pressure is a calculated value determined by measuring the actual pressure at a given weather station and correcting it for altitude. 

Atmospheric pressure is measured by surface weather stations across the globe. Since the elevation of these stations can vary significantly from the coast of British Columbia to the Rocky Mountains, station pressure (the actual pressure measured at the station) is converted to sea level pressure (the pressure that would exist if that station was at sea level). Doing so simplifies the pressure analysis, allowing meteorologists to compare pressure at different locations.

The mathematics take into consideration station altitude, station temperature, and minor instrumentation corrections. It also includes several assumptions, such as how temperature changes with altitude, which at times, can lead to incorrect values. Erroneous data, if identified, can be ignored or smoothed over while doing a hand analysis of isobars on a weather map.