RRFS Forecast Radar versus MRMS Observations

MRMS and RRFS can both show radar-like colors, but they answer different questions. Confusing the two can turn a forecast storm into an apparent observation.

MRMS: what the radar analysis is showing

The MRMS viewer presents radar-derived guidance from NOAA’s Multi-Radar Multi-Sensor system. The reflectivity loop is a sequence of processed observations. Its latest frame has a valid time and a processing delay; “live” does not mean instantaneous.

Use reflectivity to follow echo development and motion over the observed period. Color intensity alone does not establish exact rainfall at the ground, precipitation type or severity. Beam geometry, terrain, non-weather echoes and missing coverage can affect what appears. Echo-top and lightning layers, when available, have their own meaning and update times.

RRFS: a model’s predicted evolution

The RRFS viewer displays forecast guidance, including simulated radar reflectivity. Its run time and forecast hour describe a prediction. Other selections include visibility, ceiling, lightning flash density and available upper-air wind layers. These are model products, not observed airport reports or detected lightning.

The source is labeled experimental RRFS-A in the existing viewer. Small-scale placement and timing are uncertain: an attractive simulated storm shape is not a promise that a storm will follow that exact track.

Compare times before patterns

  1. Check the newest MRMS valid time and whether observations appear fresh.
  2. Choose an RRFS forecast valid near the same time.
  3. Compare the broad location and evolution of echoes, allowing for displacement and timing errors.
  4. Use later RRFS frames as scenarios, while continuing to monitor observations and official forecasts.

An RRFS loop is not an extrapolated continuation of the MRMS loop. A model can miss development that appears in observations, or forecast storms that do not occur.

When a map is blank or old

Check the product, opacity, frame count and timestamps. An unavailable layer is not proof that no weather exists. Report persistent stale data with the page and displayed times. Both viewers are available without signing in; Premium is not required to inspect them.

For warnings and safety decisions, use the National Weather Service or your official local service. Learn about the observation source at NOAA MRMS.