Prediction of Large-Scale Cloudiness and Airframe Icing Conditions by Machine Methods

Abstract

Adiabatic vertical velocities are computed for atmospheric layers and used to modify dewpoint-depression fields in twelve-hourly steps. Horizontal advection of moisture is accommodated by the Jacobian operator with height and dewpoint-depression fields as arguments. Assuming a certain correspondence exists between dewpoint-depression and amount of cloudiness, 24-, 36-, and 48-hr cloud forecasts are made for specific atmospheric layers; for example, 850?700, 700?500, 500?300, and 300?200 mb. For the lower two layers, airframe icing forecasts are produced on the basis of predicted conditions of cloudiness, temperature, and lapse rate. The 4-layer cloud forecasts in combination with a persistence term are converted to measures of total cloud cover and verified against machine nephanalyses based upon surface reports. Some cloud forecasting skill over persistence is evident in the model.