The High-Resolution Ensemble Forecast (HREF) System and Applications for Aviation Forecasting

NCEP currently plans to implement Version 2 of the High-Resolution Ensemble Forecast (HREF) system in October 2017. This upgrade is intended to effectively get the popular Storm-Scale Ensemble of Opportunity (SSEO), a set of post-processed products developed by the Storm Prediction Center, into NWS operations. HREF takes advantage of current and time-lagged high-resolution model runs, and the new CONUS version consists of eight members, all run at a horizontal resolution of approximately 3 km. The members over CONUS are the two most recent runs of: the NAM nest, the ARW and NMMB high-resolution window (HiResW) runs, and a new second HiResW ARW member configured to be similar to the National Severe Storms Laboratory ARW run. Version 2 of HREF also adds domains for Alaska, Hawaii, and Puerto Rico; these domains only utilize the HiResW and have six members.

The HREF aggregates existing high-resolution model runs, and produces probability and mean and probability-matched mean fields for a number of parameters covering aviation, precipitation, severe storm, winter weather, and general forecasting. This version of the HREF also introduces neighborhood probabilities for more isolated fields (e.g., simulated radar reflectivity), resulting in more useful products than is provided by the point probability output of HREF version 1. The new version also makes products available at least 90 minutes earlier than both the old version of the HREF and the SSEO.

EMC’s Model Evaluation group played a major role in the formal evaluation of this system, and specific forecasting examples relevant to aviation forecasting, including intense convection, cloud ceiling, and visibility will be presented.