humidity is important
Yes palgia and others. If you take my base airport at 317 ft AMSL, 15deg C air temp and 10deg C dew point the density altitude is 550ft when the baro reads 1013mb. Now the glass falls to 1000mb. What’s 13mb? Well in consequence the density altitude jumps up to 1000ft… nearly doubles. Suppose barometer and dew point stay the same at 1000mb and 10deg C but the day hots up. What happens? Well the relative humidity falls for one thing. At 20deg C the relative humidity has fallen from 72% to 53% and the density altitude is now 1583ft … more than 1000ft higher than the chart. Temperature goes on rising everything else remains constant but the day hots up to 25deg C… now the relative humidity is 39%, much more pleasant under the armpits but the density altitude is 2153ft which is 1800ft more than the chart! Finally for the sake of argument the day tops off at 30deg C still with baro and dew point stuck at 1000mb and 10 deg C. What’s the relative humidity and density altitude now? Answer 29% and 2712ft. Now from beginning to end of this example the relative density of the air has only changed by 5% - it was 97% first thing and is now 92%. But it feels so fresh now from the cool and damp in the morning. I’m not going to have lift and icing problems am I?