The Relationship of Precipitation and Cloudiness to Some Predictors from the Nmc Six-Layer Model

摘要

Implementation of the six-layer primitive equation model at the National Meteorological Center (NMC) in mid-1966 opened the way for the production, on a physically-sound basis, of a number of predictors expected to be useful in forecasting cloudiness and precipitation. These are used, objectively and subjectively, to produce NMC forecasts which appear on facsimile in various formats, including the depiction of predicted weather at specified synoptic times and forecast precipitation probabilities and amounts for certain periods. The availability of a large number of quality prognostic charts and forecasts has not, however, obviated the necessity for the field forecaster to add detail, in time and space, to the guidance forecasts. Aside from short-term extrapolation and consideration of local effects, such as orography, it seems likely that the best opportunity for supplementing guidance received from NMC is through judicious use of some of the numerically derived parameters which are routinely available. For this, the forecaster needs objective techniques and an understanding of the behavior and effects of the predictors. Such a calibration on a regional basis - the content of this memorandum - is intended to provide some assistance toward using the products more systematically. Emphasis will be principally on Mean Relative Humidity (RH), Vertical Velocity (VV), and Lifted Index (LI). (Author)