Ongoing Development of the Hourly-Updated Version of the NAM Forecast System

The North American Mesoscale Rapid Refresh system (NAMRR) is an hourly-updated version of the North American Mesoscale (NAM) forecast system and its data assimilation system. The current version of the NAM, upgraded in August 2014, provides 84 hour forecasts for its large 12 km domain and 60 hr forecasts for its four high-resolution nested domains 4 times per day at 00, 06, 12, and 18 UTC. The NAM Data Assimilation system currently performs an atmospheric analysis only every 3 hours and on its 12 km North American domain - there is no cycling of its nested domains. The NAMRR, in contrast, features an hourly forecast and assimilation cycle. Furthermore, the NAMRR also features a data assimilation cycle for its 3 km CONUS and Alaska nested domains in addition to its North American 12 km domain. All forecasts from the NAMRR are a minimum of 18 hours in length, and to maintain compatibility with the current operational NAM, 60 hr nested and 84 hr large domain forecasts are issued at 00, 06, 12, and 18 UTC. The NAMRR also plays a significant role in the development of the High Resolution Ensemble Forecast system and its rapid update component (HREF and HREF-RR, respectively). The NAMRR will form the foundation of one half of this system, while the Rapid Refresh and High Resolution Rapid Refresh systems will form the basis of the other half. A description of the NAMRR, applications to case studies, and a discussion of ongoing and future work will be presented.