The NCEP SREF System is an ensemble forecast system composed of 21 ensemble members generated from multiple models (Eta, WRF, RSM), multiple physical schemes and breeding of initial conditions. The forecast domains cover the Continental US (CONUS), Alaska and Hawaii regions. SREF System was implemented operationally in 2001 and has since then been upgraded every year. In 2002, it was extended to aviation weather. Recently, the ensemble probabilities of ceiling, visibility, flight restrictions and fog were added. One of the goals for the NCEP SREF System is providing probabilistic guidance on both regular and aviation weather to local forecasters.

In this paper, the SREF's aviation forecast will be briefly introduced, including its framework, new configuration, and the generation of the ceiling/visibility related ensemble products. The SREF aviation weather forecast is still experimental but routinely displayed on NCEP website for reference by local forecasters and NCEP Aviation Weather Center(AWC).

The grid-to-grid objective verifications of these four aviation weather products over whole domains are extremely difficult because observational data in gridded format are still not available. Current verification strategy is asking the local forecasters at various regions to evaluate what they are interested by and to send their feedbacks, comments and suggestions to NCEP. In such a forecast center through local forecaster interactive communication, we hope to gradually improve and upgrade the four aviation weather ensemble products.