The RRFS line is NOAA's deterministic Rapid Refresh Forecast System run, which is also the ensemble's control member. M1–M5 are the five perturbed members NOAA publishes (NCEP's full REFS blends 14). The previous run adds the same six from six hours earlier, aligned by valid time, which is how NCEP builds its time-lagged ensemble. Values are the model's own at the 3 km grid cell containing this point, with no smoothing, bias correction or blending (those come next). How this works.