Resumen
In this work, a model for the short term prediction of the temperature of formation of radiation fogs is developed. the model is generated from a lineal relationship between the relative humidity and the air temperature, that in function of it the temperature of saturation of the air mass is stablished. the subsequent dcrease of temperature, necessary to produce the phenomenon (""interval of fog"") is determined considering a minimum quantity of the awater vapour that the air should contain in order that the products of condensation reach the concentration and necessary size to stablish the condition of fog. the calidity of the model is verified comparing their output upon applying it by cases of radiation fog observed in three stations of the half basin of the river Duero (Salamanca, Valladolid and Zamora), in several intervals of time, with the corresponding real values of fog formation temperature.