HRRR

At a glance

Convection-allowing, which is the point.

Most weather models are too coarse to contain a thunderstorm, so they estimate the effect of convection statistically rather than simulating the storms themselves. At 3 km, HRRR is fine enough to grow individual storms in the model. That is what makes a forecast radar image meaningful at all.

Each run also starts from what the radars are actually seeing. HRRR takes in radar data every 15 minutes over the hour before it runs, so each forecast begins close to what is actually happening.

That is also the honest limitation. A convection-allowing model produces storms that are realistic in character — the right kind of weather, in roughly the right area, at roughly the right time — without being right about any particular cell. Treat the shape and timing of a system as useful, and the exact position of a cell as not.

Why the timeline is a mix of runs.

HRRR runs every hour, but only four of those runs each day go the distance. The hourly runs reach 18 hours ahead, and the 00, 06, 12 and 18 Z runs reach 48.

For every hour, the app uses the newest run that has posted it. So the near hours come from a run that may be minutes old, while hours 19–48 come from the last long run. As that run ages it covers less: a 48-hour run launched at 12 Z reaches only 36 hours ahead by 00 Z. The hours it no longer reaches are filled by RRFS until the next long HRRR run posts.

The color bar under the slider shows where each hour came from. Light green is the newest HRRR run, dark green an older HRRR run still serving a near hour, amber the long HRRR run, and brown RRFS. The mix shifts over the day, and nothing is wrong when it does.

When frames appear.

A run is not available the moment its cycle time passes. It has to be computed and published first. Timed from NOAA's own data on 30 September, an HRRR run's first files posted 51 to 60 minutes after its cycle time. A long run reached hour 48 about 1 hour 45 minutes after it, and one took 2 hours 16.

The app checks for new frames continuously and shows the newest it has. There is no refresh button because there is nothing for you to trigger.

What Radar Forecast takes from it.

• Composite reflectivity — the forecast radar frames themselves, rendered with the same color table as the observed MRMS frames so the two are comparable.
• Winds aloft — the wind field at each level the wind table reports, sampled along the route every 50 nautical miles at the time you cross each point.

Both come from the same run as that hour's radar frame, so where RRFS supplies an hour, its winds do too. Observed radar to the left of "now" is MRMS, not HRRR. Surface fronts come from WPC and forecast weather type from NDFD; those are separate products on the same timeline.

Compared with what actually happened

Rather than ask you to take the model's word for it, the site publishes side-by-side frames of the forecast against the observed radar for the same valid time.

See forecast versus actual

Sources

• NOAA Global Systems Laboratory, HRRR.
• NOAA Environmental Modeling Center, HRRR.
• Posting times: file timestamps on NOAA's public HRRR archive, noaa-hrrr-bdp-pds, 00, 06 and 12 Z runs of 30 September 2026.