The High-Resolution Rapid Refresh (HRRR) is NOAA's 3-km, hourly updated, convection-allowing weather model for the United States. Each run starts from fresh observations, including radar data, which makes it a tool for the next several hours to two days rather than the week ahead.
How often it runs and how far ahead
Over the contiguous United States the HRRR runs every hour. Most runs go out 18 hours, and the 00, 06, 12 and 18 UTC runs go out 48 hours.
The 48-hour runs arrived with HRRR version 4, which took effect 12/02/20. A separate Alaska version runs every third hour.
Starting from what radar sees
Radar data is assimilated, meaning blended into the starting state, every 15 minutes during the hour before each run. Version 4 added the HRRR Data Assimilation System, a 36-member, 3-km ensemble that assimilates radar reflectivity directly.
That gives storms already on radar a head start in the first hours of the forecast, instead of leaving the model to build them from nothing.
How forecasters and chasers use it
Because the HRRR is a convection-allowing model, it outputs simulated radar reflectivity and storm-scale fields such as updraft helicity. Forecasters look at when storms first develop in the model, whether they stay discrete or merge into lines, and how that picture shifts from one hourly run to the next.
Status and limits as of October 2026
As of October 2026, HRRR version 4 is still operational. The Rapid Refresh Forecast System (RRFS) is scheduled to become operational on 10/14/26, but NOAA has said the HRRR is not being retired with it, and the HRRR supplies two members to the new RRFS ensemble.
NOAA expects to retire the HRRR with a later RRFS upgrade. Until then, treat each HRRR run as one plausible scenario, since simulated storms can arrive early, late, displaced or not at all.