The Objective Prediction of Clouds and Precipitation Using Vertically Integrated Moisture and Adiabatic Vertical Motions

Abstract

This article describes and illustrates an objective technique of forecasting clouds, precipitation and precipitation amounts. The system is tailored to fit the specific operation of the National Meteorological Center in the use of data routinely available. It attempts to eliminate or to alleviate a number of difficulties which have plagued other objective techniques. The method follows rather closely the earlier work of Frederick Sanders, but departs importantly in the method of obtaining vertical motion and in the form and manipulation of the moisture parameter. The vertical motion is computed from objective 1000-mb and 500-mb prognoses through an adiabatic approach. Saturation thickness is used as the moisture parameter in a manner which eliminates the need for reference to specific and relative humidities. Two forecasts are illustrated in detail. The first example employs a form which obtains directly a vertical motion field, while the second by-passes this step.