Assimilation of Lightning Data Into RUC Model Convection Forecasting

Abstract

Lightning data have been used experimentally as part of the NOAA Rapid Update Cycle (RUC) assimilation method for improving cloud/hydrometeor/convection initialization. Lightning data can be used to supplement initial information on existence of convection, along with radar and satellite data and a short-range background model forecast. Radar reflectivity data is generally not available over oceanic areas and terrain-blocked areas, regions where lightning data can provide additional information. Lightning data provide conditional convection information: existence of strokes implies that convective clouds are present, but absence of strokes does not imply that convective clouds are not present. This conditional lightning information has been used within the RUC analysis to force convection to become active in the subsequent RUC model. The RUC cloud/hydrometeor analysis combines GOES and METAR cloud data with the previous 1-h RUC forecast, with radar reflectivity and lightning data in an experimental version, allowing intercomparison to ensure consistency between these data types, each with possible error modes. This initial and relatively simple technique for including lightning data will be described at the conference, along with examples of its effect. Lightning data can contribute toward an important problem for short-range numerical prediction, initialization of cloud and hydrometeor fields. Forecasts of cloud, fog, ceiling/visibility, stable and convective precipitation are dependent on accurately initializing these fields. Aviation and other transportation activities require considerable improvement from current skill level for ceiling and visibility forecasts. Model-based predictions of these fields are the main source of guidance beyond a few hours. Initial conditions for forecast models need to take into account current conditions reported by current surface observations, satellite, radar, and even lightning data, a development effort now underway for the Rapid Update Cycle (RUC).