Targeted observations at NCEP: toward an operational implementation

.During the recent years NCEP participated in the FASTEX, NORPEX and CALJET field programs with the aim of adaptively collecting extra observations in order to improve 1-4 days forecasts for threatening weather events. Based on the experience accumulated in these field experiments, a quasi-operational NWS field program, the 1999 Winter Storm Reconnaissance program was carried out over the eastern Pacific during January-February 1999. To identify the regions where the assimilation of extra observations taken at a future time could substantionally improve the ensuing forecasts of the preselected weather events the ensemble transform technique (ET, Bishop and Toth, 1996) was used. Dropsonde observations were adaptively taken by the NOAA G-lV and US Air Force C-130 planes in the sensitive areas identified by the ET technique. The impact of the adaptive observations were evaluated using parallel assimilation/forecast cycles. Combined verification statistics for sea level pressure, winds, and accumulated precipitation indicate that close to 80 % of the time the forecasts improved when started from the analyses enhanced by the dropsonde data