GFS vs HRRR
GFS or HRRR: which is better for US coastal sailing?
They answer different questions. GFS covers the whole world out to 16 days. HRRR covers the continental US and nearby waters at 3 km, updates every hour, but only looks about 18 hours ahead (longer on some runs). Use HRRR for sea breezes, squall lines and thunderstorms today, GFS for the days ahead.
| GFS | HRRR | |
|---|---|---|
| Provider | NOAA / NCEP | NOAA / NCEP |
| Type | Global model | Regional model |
| Area | Global | Continental US & coastal waters |
| Grid size | about 13 km | about 3 km |
| Updates | 4 times a day | Every hour |
| Looks ahead | 16 days | 18 hours |
| Data licence | Public domain (US Government) | Public domain (US Government) |
Choose GFS when
- You are looking more than a day ahead.
- You are anywhere outside the US.
- You want the big picture for a passage.
Choose HRRR when
- You are in US coastal waters and the next 12 to 18 hours matter.
- You are watching thunderstorms, sea breezes or fronts coming through.
- You want the freshest forecast, updated every hour.
On the water
Start with GFS for the plan, then switch to HRRR as the day gets close.
Figures come from the Ilma catalog and the providers' own pages. Forecast skill changes as models are upgraded, so this page describes what each model is built for, not a ranking.