Abstract
For airโsurvey work and other specialised daylight flying it is important to know for some hours ahead in fine weather the amount of the sky that will be covered by cloud and the height at which the cloud will exist. Readings of the dryโ and wetโbulb thermometers at 50 mb. intervals provide information which, when plotted on a tephigram or similar diagram, enables a forecaster to predict with useful accuracy the amount, height and thickness of clouds during the day. Temperature and dewโpoint at 4 ft. in the forecast area and the probable rise of temperature arc required to give the height of potential condensation, while the relation between the condensation temperature and the temperature of the environment is the criterion for cloud formation.
Cloud thickness is judged by the relation between the saturation adiabatic through the condensation point and the actual temperatures above, while cloud amount is estimated by the relative humidity of the environment a t the condensation level.
The application of this technique to the various situations met in dayโtoโday forecasting is described and illustrated.