Cloud Base & Freezing Level Calculator
This FREE tool is brought you by PPL Club. It should be used as guidance only and must not replace a full and detailed weather plan from the Met Office.
Cloud Base Calculation
The height of the convective cloud base is calculated using the surface air temperature and the dew point temperature. The difference between these two values is known as the "spread". As a parcel of unsaturated air rises from the surface, it cools at a steady rate called the Dry Adiabatic Lapse Rate (DALR), which is approximately 3 dg C per 1,000 feet.
Simultaneously, the dew point of that same parcel of air also drops as it rises, but at a much slower rate of about 5 dg C per 1,000 feet. The cloud base forms at the altitude where the cooling air temperature meets the falling dew point temperature. At this point, the air is saturated, and the water vapour condenses into visible cloud droplets.
Because the temperature and dew point converge at a rate of 2.5 dg C for every 1,000 feet of altitude, a simple formula can be used:
Freezing Level Calculation
The freezing level is the lowest altitude in the atmosphere where the air temperature is 0 dg C. This calculation relies on the surface temperature and the Environmental Lapse Rate (ELR), which is the rate at which the air temperature cools as altitude increases. For general aviation and meteorological calculations, the ICAO (International Civil Aviation Organisation) Standard Atmosphere lapse rate is used, which is approximately 2 dg C per 1,000 feet.