WINTER WEATHER FORECASTING THROUGHOUT THE EASTERN UNITED-STATES .2. AN OPERATIONAL PERSPECTIVE OF CYCLOGENESIS

The complex combination of synoptic and mesoscale interactions, topogr aphic influences, and large population densities poses a multitude of challenging problems to winter weather forecasters throughout the east ern United States. Over the years, much has been learned about the str ucture, evolution, and attendant precipitation within winter storms. A s a result, numerous operational procedures, forecast applications, an d objective techniques have been developed at National Weather Service offices to assess the potential for, and forecast, hazardous winter w eather. A companion paper by Maglaras et al. provided an overview of t he challenge of forecasting winter weather in the eastern United State s.This paper focuses on the problem of cyclogenesis from an operationa l perspective. Since pattern recognition is an important tool employed by field forecasters, a review of several conceptual models of cyclog enesis often observed in the east is presented. These include classica l Miller type A and B cyclogenesis, zipper lows, 500-mb cutoff lows, a nd cold-air cyclogenesis. The ability of operational dynamical models to predict East Coast cyclones and, in particular, explosive cyclogene sis is explored. An operational checklist that utilizes information fr om the Nested Grid Model to forecast the potential for rapid cyclogene sis is also described. A review of signatures related to cyclogenesis in visible, infrared, and water vapor satellite imagery is presented. Finally, a study of water vapor imagery for 16 cases of explosive cycl ogenesis between 1988 and 1990 indicates that an acceleration of a dry (dark) surge with speeds exceeding 25 m s(-1), toward a baroclinic zo ne, is an excellent indicator of the imminent onset of rapid deepening .