Turbulence is the weather hazard most passengers experience and the one forecasters have had the least ability to pin down. It happens in clear air, at specific altitudes, in pockets that can be a few miles wide, and traditional forecast models are built to describe much larger features than that.
On July 30 the National Weather Service’s Aviation Weather Center put a new tool into operation to close some of that gap. The Graphical Turbulence Guidance Nowcast, or GTGN, updates a turbulence analysis every fifteen minutes across 51 altitude levels.
The Difference Between A Forecast And A Nowcast
This is the part that matters and the part that gets glossed over. A forecast is for planning. It tells a dispatcher which route to file hours before departure. A nowcast is for the aircraft that is already flying and needs to know what the next twenty minutes look like.
Previous turbulence products were useful for route selection. GTGN is built to inform decisions in the air, which is a different job with a different tolerance for latency.
The practical version of that distinction is familiar to anyone who has flown. A crew hits unexpected chop, asks for a different altitude, and waits while controllers and dispatch work out whether the ride is better up or down. A nowcast is an attempt to answer that question before the request gets made.
Fifty One Altitudes Is The Headline Number
GTGN produces output at 51 separate levels, beginning 100 feet above ground level and continuing to 50,000 feet. Turbulence is intensely vertical. A layer that is unusable at 34,000 feet can be smooth at 30,000, and a product that averages across altitude bands hides exactly the information a crew needs.
Covering from near the surface all the way to the top of commercial airspace also means the same tool serves general aviation in the low levels and airliners in the flight levels.
Three Kilometer Resolution Changes What Is Visible
Horizontally, GTGN matches the resolution of its base model, the High Resolution Rapid Refresh, at 3 kilometers over the continental United States. That is fine enough to represent individual mountains and individual thunderstorm cells.
Those are precisely the features that generate the roughest air. Mountain wave turbulence downwind of a single ridge and convective turbulence near one storm cell are local phenomena, and a coarser grid smears them into nothing.
Resolution also matters for what does not get flagged. Overly coarse guidance that paints a broad region as rough leads crews to route around air that was fine, which costs fuel and time. Sharper grids reduce false alarms as much as they catch real hazards.
It Covers All Three Turbulence Sources
The system addresses clear air turbulence, mountain induced undulations, and convective turbulence from thunderstorms. Historically those have been handled by different products with different assumptions, which left crews mentally stitching together several pictures.
Clear air turbulence is the one worth singling out, because there is nothing to see. No cloud, no radar return, no visual warning. It is responsible for a large share of injuries in the cabin for exactly that reason.
Where The Data Comes From
GTGN blends ground based lightning data, satellite derived data, pilot reports known as PIREPs, and surface weather station observations called METARs. Its short term analysis comes from the NCAR Turbulence Detection Algorithm and the HRRR model.
The inclusion of PIREPs is the human part of the system. A pilot reporting moderate chop at a specific altitude feeds back into the picture other aircraft are looking at, which is a genuinely elegant loop.
Who Built It And Why That Matters
The Aviation Weather Center developed GTGN with the National Center for Atmospheric Research and the Cooperative Institute for Research in the Atmosphere at Colorado State University, sponsored by the Federal Aviation Administration and moved into operations through the Aviation Weather Testbed.
That testbed pathway is the unglamorous machinery that turns research into something a working pilot can open. Plenty of good atmospheric science never makes that transition.
There is a longer term reason this work is getting funded. Clear air turbulence encounters have been trending upward in several analyses, with changes in jet stream behavior cited as a likely contributor. Better detection is partly a response to a hazard that is not staying constant.
What This Means For Passengers
Indirectly, better information for the flight deck means better decisions about when to turn the seatbelt sign on and when to move a cabin crew out of the aisle. Most turbulence injuries happen to people who are not seated and secured.
It does not mean fewer bumps. Turbulence forecasting improves avoidance and preparation, not the atmosphere. If you want to get better at reading conditions yourself, our guide to reading the radar without waiting for a forecaster is a reasonable starting point.
How To Access It
GTGN is available on the Aviation Weather Center website, including a mobile friendly version pilots can use in flight. Raw data in the standard GRIB2 binary format is published on NOMADS for anyone building their own tools on top of it.
That last part is worth noting. Publishing the raw grids means third party flight planning apps can integrate the same data, which is usually how a government product actually reaches most of its users.
Frequently Asked Questions
What is GTGN?
The Graphical Turbulence Guidance Nowcast, a National Weather Service tool that provides frequently updated turbulence analysis for pilots. It debuted on July 30, 2026.
How often does it update?
Every fifteen minutes, or four times per hour.
What altitudes does it cover?
51 separate levels, starting at 100 feet above ground level and extending to 50,000 feet.
What types of turbulence does it include?
Clear air turbulence, turbulence caused by mountains, and convective turbulence associated with thunderstorms.
How is a nowcast different from a forecast?
Forecasts support planning a route before departure. A nowcast supports decisions during the flight, using very recent observations and short range analysis.
Can the public access the data?
Yes. The tool is on the Aviation Weather Center website with a mobile friendly version, and raw GRIB2 data is available on NOMADS.
