Development of an Hourly-Updated NAM Forecast System

The current NCEP North American Mesoscale Forecast System (NAM) provides forecasts out to 84 hours four times a day at 00, 06, 12, and 18 UTC while its data assimilation component, the NAM Data Assimilation System (NDAS), performs atmospheric analyses every three hours on its 12 km North American domain. The work presented here discusses the ongoing process of transitioning this system into one which features an hourly cycle, known as the NAM Rapid Refresh (NAMRR). The developmental NAMRR performs an analysis and subsequent forecast at hourly intervals with both the 12 km North American domain as well as a 4 km nest domain which covers the contiguous United States. Like the NAM, the NAMRR assimilates a wide variety of conventional and satellite radiance observations but, similar to the Earth Systems Research Lab's Rapid Refresh Version 2, it also features a radar reflectivity-based initialization of cloud thermodynamic and hydrometeor fields through the application of a diabatic digital filter initialization step for each forecast. A description of the developmental NAMRR forecast system along with applications to severe weather events and wind energy forecasting will be presented. The development of the NAMRR, in conjunction with the current RAPv2 and High Resolution Rapid Refresh systems, represents an important step toward the eventual realization of a high-resolution, rapidly updated ensemble forecast system in NWS operations.