RAP = RApid Refresh model — An hourly, short range model for the continental US with a horizontal resolution of 13 kilometers, similar to the NAM

The Rapid Refresh model hourly forecasts extend out only18 hours, but a recent model revision in 2020 has the RAP forecast extend out to 54 hours. These longer forecast RAP model runs are done four times daily at 03z, 09z, 15z and 21z.

Of interest is that the RAP model uses the same data input as the GFS. This is different from the other hourly model, the HRRR.