(Pressure Height); the height that corresponds to a given value of atmospheric pressure according to the ICAO standard atmosphere. In aviation, pressure altitude is the indicated height when an altimeter is set to 1013 hPa (29.92 in/Hg).
It is used to calculate aircraft performance and for aircraft flying above 10 000 feet MSL, known as the indicated Flight Level of a pressure altimeter; therefore, it is the indicated height above the 1013.2 hPa as a constant-pressure reference.
Density Altitude (Density Height); Pressure altitude that has been corrected for non-standard temperature. In other words; the height that corresponds to a given value of atmospheric pressure according to the ICAO standard atmosphere, given the local deviations of temperature and pressure from the standard atmosphere.
Actual atmospheric conditions specifically to the surrounding area or portion of air space.
A forecast is a prediction of future weather made by meteorologists. Meteorological Forecast or Weather Forecast is the expected meteorological conditions for a specific period and for a specific area or portion of air space.