What Barometric Pressure Should I Use?
You should use what is called STATION PRESSURE: This is the pressure that is observed at a specific elevation and is the true barometric pressure of a location. In general, for every thousand feet of elevation gain, the pressure drops about 1 inch of mercury. For example, locations near 5000 feet (about 1500 meters) above mean sea level normally have pressures on the order of 24 inches of mercury.
Some people mistakenly use the ALTIMETER SETTING: This is the pressure reading most commonly heard in radio and television broadcasts. It is not the true barometric pressure. Instead it is the pressure “reduced” to mean sea level using the temperature profile of the “standard” atmosphere, which is representative of average conditions over the United States at 40 degrees north latitude.
MEAN SEA LEVEL PRESSURE: This is the pressure reading most commonly used by meteorologists to track weather systems at the surface. Like altimeter setting, it is a “reduced” pressure which uses observed conditions rather than “standard” conditions to remove the effects of elevation from pressure readings. This pressure should not be used either.