The GFS weather model

At a glance

What GFS is

The GFS is the American entry in the group of global weather models. It is the model that gives a quick answer for the whole planet: it covers every region, runs on a regular schedule, and has a long record that forecasters have learned to read.

It simulates the atmosphere by dividing it into a three-dimensional grid and stepping forward in time. The grid spacing of about 13 kilometers is fine enough to draw a storm system, a front or a jet stream, but too coarse to draw an individual thunderstorm. For that detail, forecasters switch to a high-resolution regional model such as HRRR.

Because it is deterministic, one GFS run is one possibility. Its companion ensemble, GEFS, runs the same kind of model many times to show how much that possibility can change.

Where it does well

• Global coverage on a fixed schedule, four times a day, with output for 16 days.
• A full set of fields, from pressure and temperature to upper-air winds, so it works for almost any question about the large-scale pattern.
• Long public history. Because the GFS has run in similar form for years, forecasters know its habits, which makes it easier to read than a new model.
• A good tool for reading the setup three to ten days ahead: where the troughs and ridges are, and how storms may track.

Where it falls short

• It is one run. A single GFS map can flip from one cycle to the next, so look at the trend over several runs and at the ensemble.
• A 13 km grid cannot draw individual thunderstorms or narrow snow bands. Treat small-scale features as hints.
• The farther out, the less detail you can trust. A map for day 14 describes a pattern and not a street.
• Snowfall maps built from the GFS often use an assumed snow-to-liquid ratio. A fixed 10:1 map can overstate near-freezing snow and understate very cold snow.

What it is typically used for

• Finding the large-scale pattern and the track of storms several days out.
• Checking when cold air or a warm-up arrives, using 850 mb temperature and thickness.
• Comparing with another global model at the same valid time to see whether the storm story agrees.
• Serving as the starting point for soundings and for model-based point forecasts at a location.

How to see GFS in 4070

The GFS is in Model Explorer under Global Models, where you choose a field, a run and a forecast hour. Everything below is part of 4070 Pro, which starts with a seven-day free trial.

• Fields include 1 to 60 hour precipitation totals, rate of precipitation, simulated radar, snow depth and a 10:1 total snowfall field drawn by WDS, plus thickness, 850 mb temperature with pressure and precipitation, 10 meter wind and gusts, surface CAPE and CIN, and upper-air maps from 925 to 200 mb including 500 mb heights and wind and 500 mb vorticity.
• Soundings: a supported GFS map lets you click a point and open a forecast sounding with a skew-T and hodograph, and the point stays pinned as you change forecast hour.
• Compare Models puts the GFS beside another compatible model at the same valid time, and Compare Cycles wipes between an earlier and a newer GFS run.
• Plumes overlay the four most recent GFS runs at a U.S. point on a 0.25 degree grid, and Storm Tracks follows the four most recent GFS runs for developing lows.

Learn what the labels mean in how to read weather models.

How it fits with the other models

The GFS and the ECMWF IFS are the two global models most forecasters check first. They are built by different agencies with different methods, so they can place the same storm differently, which is the reason to compare them at the same valid time. NOAA AI-GFS is a newer machine-learning model from the same agency. For details inside a day or two, step down to HRRR. For confidence, step across to GEFS. Our guide on which model is most accurate explains why the best choice depends on the question.

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.