WRAL WeatherCenter Blog

Can the dew point or temperature help you predict the level of the clouds?

Posted January 26, 2008 12:19 p.m. EST

MIKE MOSS SAYS:      Rona,        They can, but you have to know both quantities. The height of a cloud base that results from lifting of near-surface air (this doesn't apply to all clouds) can be estimated based on the surface values of temperature and dew point, since the height at which a cloud will form is roughly the height at which the temperature and dew point would become equal due to expansion of the air as it rises to regions of lower pressure. You can estimate this knowing that for unsaturated air, the temperature will decrease about 10 degrees C per vertical kilometer while the dew point will fall about 2 degrees C per kilometer. Translated a bit, there is an approximation for cloud base height in feet above ground level that is   H = 400 (T-Td), where T and Td are temperature and dew point at the surface in degrees C.