NOAA schedules 15-minute GTGN turbulence nowcasts for June 29, 2026

NOAA/NWS has scheduled the Graphical Turbulence Guidance Nowcast (GTGN) for operational implementation on or about June 29, 2026 at 1200 UTC.

The useful change is operational: GTGN turns turbulence guidance into a 15-minute nowcast, built for conditions that can evolve faster than a standard forecast cycle.

What GTGN Adds

GTGN starts from a short-term Graphical Turbulence Guidance (GTG) forecast, then blends in recent turbulence observations to produce a near real-time analysis. NOAA says the product is meant to support the aviation community, but it is not a substitute for forecaster-issued turbulence SIGMETs.

The notice lists these inputs:

• pilot reports
• automated in situ eddy dissipation rate reports
• radar-derived EDR from NCAR's Turbulence Detection Algorithm
• estimated EDR from lightning data
• METAR data

The output is EDR, an aircraft-independent turbulence metric. NOAA says the horizontal domain follows the 3 km HRRR CONUS domain used by GTG, with vertical output from 100 feet and then every 1,000 feet up to 50,000 feet.

Timeline and Access

The planned operational start is June 29, 2026 at 1200 UTC. If that day is a Critical Weather Day, Enhanced Caution Event, or another significant weather period, NOAA says implementation will move to the next suitable weekday.

NOAA also documents a machine-readable NCEP/NOMADS data path:

https://nomads.ncep.noaa.gov/pub/data/nccf/com/gtgn/prod/gtgn.YYYYMMDD/

The filename pattern is:

gtgn.tHHMMz.3km.grib2

That distribution detail matters because it means GTGN can be monitored, archived, and exposed through tools rather than only viewed on a web display. The notice says each 3 km file is about 31 MB and identifies the turbulence field as Eddy Dissipation Parameter (EDPARM).

Why this matters for aviation workflows

GTGN is useful when the question is not "what might turbulence look like in several hours?" but "what is the best current analysis after the latest reports and observations?" That makes it relevant for dispatch dashboards, route monitoring, pilot briefings, event review, and comparing recent turbulence reports against the model background.

The 15-minute cadence is the key operational feature. It lets the product react to newly observed turbulence signals while still staying tied to the physically consistent GTG forecast field.

Why this matters for GribStream

GribStream already serves HRRR and NOAA aviation guidance such as DAFS GTG. GTGN would add a different layer: a high-frequency turbulence nowcast that can sit alongside forecast guidance in the same aviation workflow.

The feed is future-dated, so there is nothing to query through GribStream yet. Once NOAA turns it on, the value for GribStream customers is straightforward: consistent API access to live and historical turbulence nowcasts without building a one-off GTGN ingestion pipeline.

Sources

• NWS Service Change Notice 26-46, "Implementation of the Graphical Turbulence Guidance Nowcast (GTGN)": https://www.weather.gov/media/notification/pdf_2026/scn26-46_gtgn_implementation.pdf
• NWS Public Information Statement 26-08, experimental GTGN comment period: https://www.weather.gov/media/notification/pdf_2026/pns26-08_ExpGTGN.pdf
• GTGN display location listed by NOAA: https://aviationweather.gov/gfa/#obs