The NAM 3 km Nest weather model

At a glance

What NAM 3 km Nest is

The NAM is a regional model: it covers North America and not the whole planet, which lets it use a finer grid than a global model for the same computing cost. A nest is a smaller, still-finer box placed inside the larger model. The 3 km nest over the contiguous United States is fine enough to draw individual storms and bands of heavy snow.

It sits between the hourly HRRR, which looks ahead 18 to 48 hours but refreshes constantly, and the 12 km NAM, which goes out to 84 hours with less detail. The nest runs four times a day, so it updates less often than HRRR, and it goes stale between cycles.

The NAM is also changing. The National Weather Service has published notices planning to retire the NAM 12 km and its nests and replace them with the Rapid Refresh Forecast System (RRFS), a 3 km deterministic system that updates hourly. As of the September 9, 2026 update, both changes are set for October 14, 2026. The date has moved more than once, so the notice itself is the place to check. 4070 also offers RRFS as an experimental model.

Where it does well

• Storm-scale detail: the 3 km grid can draw individual storms, snow bands and sharp temperature gradients.
• A longer range than most high-resolution models. 60 hours reaches two days ahead and further than the 18-hour runs of HRRR.
• A broad field set that includes simulated radar, helicity, CAPE and CIN, echo tops, visibility, ceiling and upper-air maps.
• A different model, with different physics, from HRRR. When two high-resolution models agree on timing, that is more convincing than one.

Where it falls short

• It runs only four times a day, so a run can be six hours old by the time the next one arrives.
• The domain is limited to the United States in this nest.
• Like any model that draws individual storms, it can draw them in the wrong place. A single run is one possibility.
• The NAM is scheduled to be retired. Plan on RRFS and the models that follow it for the same job.

What it is typically used for

• Looking at tomorrow’s storms and snow bands when HRRR’s shorter runs have stopped.
• Comparing the timing of a front or a snow band with HRRR.
• Checking cold-air setups, wind gusts, visibility and ceiling for the next two days.

How to see NAM 3 km Nest in 4070

The NAM 3 km Nest is in Model Explorer under Mesoscale Models. It is part of 4070 Pro, which starts with a seven-day free trial.

• Fields include 1 to 60 hour precipitation totals, rate of precipitation, 1 km and composite simulated radar, snow depth, thickness, 850 mb temperature with pressure and precipitation, 10 meter wind and gusts, CAPE and CIN, helicity, echo tops, ceiling, visibility and upper-air maps.
• Regions include the United States, Alaska, Hawaii and sectors such as the Northeast and the Southeast U.S.
• Plumes use the three most recent NAM Nest runs at a U.S. point, alongside the other models.
• Compare Models puts it beside another compatible model at the same valid time.

How it fits with the other models

Use HRRR for the next few hours and the NAM 3 km Nest for the next two days. The NBM blends many models, including high-resolution ones, into a calibrated forecast. For the large-scale setup, use the GFS. Our guide to reading models explains runs and valid times.

Specifications change when agencies upgrade their models. The Sources below link to the producing agency. Official National Weather Service forecasts, watches and warnings remain the authority for what is expected where you live.