The Sea-Level Pressure map displays the current pressure, reduced to sea level, in inches of mercury. The pressure data are reduced to sea level because surface pressure is directly proportional to elevation. Locations at higher elevation (e.g., western Oklahoma) will always have a lower surface pressure than locations at lower elevations (e.g., eastern Oklahoma). By reducing all of the pressure readings to what they would be at sea level, it is possible to identify high and low pressure systems that move across the state. This map is updated every five minutes.