Forecasting low cloud and advection fog – a new method tested in the Channel Islands

Abstract Advection fog and low cloud form when moist air reaches saturation as it crosses relatively cool sea. As well as operations at sea, advection fog affects many coastal areas at times. However, manual forecasts of this type of fog have long relied on relatively crude empirical methods and little attention has been given to any improved method. In this paper, a new manual forecasting technique is presented using the wet‐bulb potential temperature of air near the surface and sea‐surface temperature, the first available from model data and the second using online or locally observed data.