NOAA tests GTGN: a 15-minute turbulence nowcast built on HRRR and observations

On February 3, 2026, NOAA/NWS issued Public Information Statement 26-08, soliciting comments through March 5, 2026 on the Aviation Weather Center's (AWC) experimental GTG Nowcast (GTGN) product.

GTGN is designed to provide a near real-time analysis of in-flight turbulence every 15 minutes, intended to complement existing turbulence guidance by blending model-based guidance with recent observations.

What GTGN is (in plain terms)

• GTGN is a nowcast: it starts with a short-term Graphical Turbulence Guidance (GTG) forecast (1-2 hours) and then updates that forecast using recent turbulence observations to produce a blended analysis.
• The output is energy dissipation rate to the one third power (EDR), which NOAA describes as an aircraft-independent metric of turbulence.

Data sources, coverage, and resolution

NOAA lists several observation inputs used by GTGN, including:

• Pilot reports (PIREPs)
• Automated in situ EDR reports
• Radar-derived EDR estimates via the NEXRAD Turbulence Detection Algorithm (NTDA)
• Estimated EDR signals derived from lightning and METAR data

Coverage and structure are tied to the underlying GTG configuration:

• The GTG forecast baseline is based on NOAA's 3-km HRRR over the CONUS, and NOAA states that domain is used as the horizontal domain for GTGN.
• Vertical output begins near the surface (listed as 100 feet) and is produced every 1,000 feet up to 50,000 feet.
• The experimental web display is upscaled to a 13-km horizontal grid and shows selected flight levels (with additional max-above/max-below summaries around 18,000 feet).

Why this matters

• Turbulence is time-sensitive: A 15-minute nowcast can capture rapidly evolving conditions that a pure model forecast may lag.
• Observation blending can help correct short-term forecast errors when recent turbulence reports indicate conditions are stronger or weaker than predicted.
• For data users, GTGN is also a signal of where aviation turbulence guidance is heading: more frequent, observation-informed updates that can be used for situational awareness, route planning, and post-flight analysis.

What this means for GribStream users

GribStream supports HRRR. Since NOAA describes GTGN as an experimental product delivered via an AWC testbed page (rather than a standard public GRIB distribution), it is not currently a GribStream feed.

If GTGN becomes available through a stable, machine-consumable distribution channel (for example via the AWS Open Data program or an official NOAA API), we will evaluate supporting it as an additional aviation-oriented product layer alongside HRRR.

Links

• HRRR

Sources

• NWS PNS 26-08 (Feb 3, 2026): https://www.weather.gov/media/notification/pdf_2026/pns26-08_ExpGTGN.pdf
• AWC experimental GTGN display: https://testbed.aviationweather.gov/gtgn/