HRRR vs NAM
HRRR or NAM: which US regional model should I look at?
Both are US regional models. HRRR has the finer grid (3 km) and updates every hour but is short-range. NAM is coarser (12 km, with finer nested areas) and looks further ahead, about 3.5 days, but updates only four times a day.
| HRRR | NAM | |
|---|---|---|
| Provider | NOAA / NCEP | NOAA / NCEP |
| Type | Regional model | Regional model |
| Area | Continental US & coastal waters | North America |
| Grid size | about 3 km | about 12 km |
| Updates | Every hour | 4 times a day |
| Looks ahead | 18 hours | 4 days |
| Data licence | Public domain (US Government) | Public domain (US Government) |
Choose HRRR when
- You want the finest detail for the next day.
- You want hourly updates.
- You are watching convective weather such as squalls and storms.
Choose NAM when
- You want a regional model that looks 2 to 3 days ahead.
- You want to compare against HRRR.
- You are outside the area where HRRR is available but in North America.
On the water
For the next 18 hours HRRR is usually the first choice in US waters. NAM covers the gap before GFS takes over.
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.