The Use of Hourly Model-Generated Soundings to Forecast Mesoscale Phenomena. Part I: Initial Assessment in Forecasting Warm-Season Phenomena.

Since late 1995, NCEP has made available to forecasters hourly model guidance at selected sites in the form of vertical profiles of various forecast fields. These profiles provide forecasters with increased temporal resolution and greater vertical resolution than had been previously available. The hourly forecast profiles are provided for all of NCEP's short-range models: the Nested Grid Model, Eta Model, and Mesoscale Eta Model. The highresolution forecasts aid in the timing of frontal passages, low-level jets, and convective initiation. In addition, through time-height cross sections of Richardson numbers, forecasters can alert pilots to the potential for clear air turbulence several hours to a day in advance. Further, the profiles are useful in prediction of cloudiness and the dissipation of low-level stratus and fog. Time-height cross sections of wind velocity have proven extraordinarily useful in visualizing and forecasting inversion heights, frontal passage timing, boundary layer depth, and available environmental and storm-relative helicity during convective events. The hourly model forecasts were found to be exceptionally helpful when combined with hourly surface observations to produce enhanced real-time analyses of convective parameters for use in very short term forecasting. High-resolution analyses of lifted index, CAPE, convective inhibition, moisture flux convergence, and 2-h changes in these fields aid the forecaster in anticipating convective trends. The introduction of model forecast error into these real-time analyses was minimized by using the latest available Eta or Mesoscale Eta Model runs. Therefore, the model data used to enhance the analyses are typically no more than 6-12 h old. [ABSTRACT FROM AUTHOR]