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The Rapid Refresh (RAP) is a NOAA/NCEP operational weather prediction system comprised
primarily of a numerical forecast model and analysis/assimilation system to initialize that
model. It covers North America and is run with a horizontal resolution of 13 km and 50 vertical layers.
The RAP was developed to serve users needing frequently updated short-range weather
forecasts, including those in the US aviation community and US severe weather forecasting
community. The model is run for every hour of the day; it is integrated to 51 hours for the
03/09/15/21 UTC cycles and to 21 hours for every other cycle. The RAP uses the ARW core
of the WRF model and the Gridpoint Statistical Interpolation (GSI) analysis - the analysis is
aided with the assimilation of cloud and hydrometeor data to provide more skill in short-range
cloud and precipitation forecasts.