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.

Update, July 4, 2026: NOAA has since replaced the June implementation plan with NWS SCN 26-62, now targeting operational GTGN implementation on or about July 28, 2026 at 1200 UTC. Evaluation data is available from the NOMADS parallel/test path, and GribStream now serves that feed as GTGN under the stable gtgn dataset code. When NOAA promotes GTGN to the production NOMADS output, GribStream expects to migrate the same dataset to that production source. See the follow-up: NOAA GTGN turbulence nowcast data is now available on GribStream.

Earlier update, May 7, 2026: NOAA initially scheduled GTGN for operational implementation on or about June 29, 2026, with 15-minute CONUS turbulence nowcasts and an operational NOMADS data feed. That notice was later replaced by SCN 26-62.

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. At publication time, NOAA described GTGN as an experimental product delivered through an AWC testbed page rather than a stable public data feed.

NOAA now publishes GTGN evaluation data through the NOMADS parallel/test feed. GribStream serves that source as GTGN while the operational production output remains future-dated, and expects to migrate the same gtgn dataset to the production NOMADS source when NOAA promotes it.

Links

• HRRR

Sources

• NWS PNS 26-08 (Feb 3, 2026): https://www.weather.gov/media/notification/pdf_2026/pns26-08_ExpGTGN.pdf
• NWS SCN 26-46 (May 7, 2026): https://www.weather.gov/media/notification/pdf_2026/scn26-46_gtgn_implementation.pdf
• NWS SCN 26-62, GTGN v1.0 implementation notice: https://www.weather.gov/media/notification/pdf_2026/scn26-62_GTGN_v1.0.pdf
• NOMADS GTGN parallel data: https://nomads.ncep.noaa.gov/pub/data/nccf/com/gtgn/para/
• AWC experimental GTGN display: https://testbed.aviationweather.gov/gtgn/