The RTNEPH (Real Time NEPHanalysis) model replaced the 3DNEPH (3- Dimensional NEPHanalysis) model in August, 1983 as the AFGWC (Air Force Global Weather Central) automated cloud analysis model. It uses a horizontal grid spacing of 25 nautical miles and uses four floating layers in the vertical. The RTNEPH uses visual and infrared data from meteorological satellites as well as surface observations, radiosonde data, and aircraft reported data to produce its analysis. A capability exists to manually modify the analysis to correct deficiencies. This nephanalysis is then used as input for AFGWC's cloud forecast models and is stored for climatological purposes by the USAF Environmental Technical Applications Center. The RTNEPH is scheduled to undergo a technical enhancement to incorporate multi-spectral techniques, use finer resolution satellite data, and produce a 12.5 nautical mile resolution analysis. Keywords: Cloud analysis, Meteorology, Nephanalysis, Polar orbiting satellite data.

The Air Force Global Weather Central (AFGWC) automated cloud analysis program (3DNEPH) produces high resolution, three-dimensional analyses of clouds over the entire globe. Up to eight analyses are scheduled per day with additional limited area analyses available on request. Horizontal grid spacing is 25 nautical miles and the vertical grid consists of 15 layers of varying thickness from the earth's surface to 55,000 feet above mean sea level. The program is a string of individual modules which process and integrate meteorological cloud information from surface, pilot, and upper air reports. An additional capability to interpret and incorporate visual and infrared satellite imagery results in high resolution, worldwide coverage. Recent advances in the techniques and methodology for interpreting satellite imagery are described. A new manual data input processor, quality control procedures, and applications are also described. An appendix provides detailed information on the high resolution terrain, geography, temperature, and background brightness (albedo) fields used to support the model. A history of the model is included and detailed descriptions of the satellite processing algorithms are also provided. Samples of displayed data using several display methods are included.

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 Central's (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.