GFS
Global Forecast SystemNOAA NCEP · 0.25° · 16 days · Every 6 hours
What This Model Is Showing
Interpretation temporarily unavailable.
The single "best guess" companion to GEFS. Sharper resolution, faster updates, no ensemble spread. The default reference for general weather forecasting.
Best single forecast, sharper detail than GEFS mean, baseline reference
500mb Heights — Atmospheric Pattern
GFS · 20 framesSea Level Pressure — Surface Systems
GFS · 20 framesHow to Read GFS Charts
GFS vs GEFS: What's the Difference?
The GFS (Global Forecast System) is a single deterministic model — it gives you one "best guess" at the future atmosphere. The GEFS is the ensemble version that runs the same model 31 times.
Think of GFS as "here's what we think will happen" and GEFS as "here are 31 possible outcomes." GFS gives sharper detail; GEFS gives you confidence information.
When to use GFS: You want the highest-resolution single forecast for pattern details, frontal timing, and specific precipitation amounts.
When to use GEFS: You want to know how confident the forecast is — especially beyond 3 days.
Most professional meteorologists check both. Use GFS for the "what" and GEFS for the "how certain."
Reading 500mb Height Contours
GFS 500mb charts show single-line contours rather than spaghetti. Each line represents a specific height value (measured in meters). The lines are drawn every 60 meters.
The flow follows the contours. Air moves roughly parallel to these height lines, from west to east in the mid-latitudes. Where lines curve southward, cold air is diving south. Where they bulge northward, warm air is pushing north.
Key values to watch: - 5880m line: Often called the "heat dome" contour. If this line is overhead in summer, expect oppressive heat - 5400m line: The rain/snow line in winter. North of this line, precipitation often falls as snow - Closed contours: A closed circle of contours means a cut-off low or a strong ridge — either way, weather will be persistent in that area
For equestrians: Follow the flow pattern. A strong westerly flow means changeable weather. A big lazy ridge means multi-day stable conditions — great for shows and events.
Forecast Hour Timing
The GFS updates every 6 hours (00Z, 06Z, 12Z, 18Z) and forecasts out to 16 days (384 hours). But skill drops significantly after day 7.
Days 1-3 (F000-F072): High accuracy. Trust it for specific timing and intensity.
Days 3-7 (F072-F168): Good for general pattern — "will it be warm or cool, wet or dry." Don't trust specific timing.
Days 7-10 (F168-F240): Pattern guidance only. "A trough may affect the region." Don't plan around specific days.
The init time matters. The 00Z and 12Z runs use more observational data (radiosondes) and are generally more reliable than the 06Z and 18Z runs. Our pipeline updates after each run, but the 00Z and 12Z frames are the ones to put the most weight on.