The second-generation operational version of the High Resolution Rapid Refresh (HRRR) model, developed at NOAA/ESRL/GSD and run operationally at NCEP, is scheduled to be updated to its next version in February 2018. The HRRR is the only operational NCEP convection-allowing model with a new run every hour. The HRRR became an operational model at NCEP on 30 September 2014, after being available to forecasters for several years previously on an experimental basis from GSD in Boulder. Currently the HRRR is run once per hour at NCEP out to 18 h at a horizontal grid resolution of 3 km. It is initialized with the RAP (Rapid Refresh model) model, which is run at NCEP at a resolution of 13 km once per hour out to 21 hours, but the HRRR assimilates radar and other data on the 3-km scale. A number of improvements to the RAP (which is scheduled to be updated at NCEP at the same time) and HRRR will be in the next version. This presentation will summarize the changes that will be made for the next operational version of the HRRR. We will then compare the two versions for some recent heavy rain/flash flooding cases in various areas across the CONUS. Examples of output from an experimental HRRR ensemble system will also be shown. In addition, we will look at some neighborhood probability forecasts using the HRRR time-lagged ensemble (HRRRTLE) as potential guidance for heavy rain events.
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