Development of a Cloud Forecast Scheme for the GL Baseline Global Spectral Model
Final rept. 1 Oct 1987-30 Sep 1989,
AIR FORCE SYSTEMS COMMAND HANSCOM AFB MA GEOPHYSICS LAB
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Using forecast relative humidity RH from a global model, several pre-existing diagnostic RH-to-cloud schemes were tested to forecast global fractional cloud cover in a postprocessor format. Since none of the schemes tested provided a superior cloud forecast when compared to Air Force Global Weather Centrals AFGWC operational 5LAYER cloud forecasts, a new RH-to-cloud scheme was developed by relating cumulative frequencies of forecast RH to cumulative frequencies of analyzed cloud cover from the AFGWC RTNEPH cloud analysis. This scheme creates a series of forecast time dependent RH-to-cloud curves that can be temporally updated to account for changes in season, cloud analysis, or forecast model, The global model used was a spectral-type developed by the Geophysics Laboratory GL using parameterized diabatic physics presently incorporated in the operational GSM global spectral model at AFGWC.