New Capabilities of the Graphical Turbulence Guidance (GTG) Product

Aircraft encounters with turbulence continues to be a concern for aviation safety and traffic routing efficiency. For strategic planning of turbulence avoidance, the National Center for Atmospheric Research has developed the Graphical Turbulence Guidance Product (GTG). As operational numerical models to date are not yet capable of resolving turbulence scales that affect commercial aircraft, GTG is based on the assumption that larger scale disturbances resolved by these models cascade down to aircraft relevant scales. GTG utilizes a number of larger scale turbulence predictors that are combined to produce clear-air turbulence (CAT), mountain wave turbulence (MWT), and low-level turbulence (LLT) forecasts. It currently runs operationally at NOAA’s Environmental Model Center based on NOAA’s Rapid Refresh (RAP) and NOAA’s Global Forecast System (GFS) and UK Met Office global models to support the World Area Forecast System (WAFS).

NCAR has recently upgraded the GTG capability to include improved LLT and convectively induced turbulence forecasts using higher grid resolution models, such as NOAA’s High-Resolution Rapid Refresh (HRRR) model.

The new CIT diagnosis is based on several in-cloud CIT diagnostics that have been mapped to a climatology of observed in-cloud energy dissipation rate to the 1/3 power (EDR) – a quantitative measure of turbulence intensity – from in-situ aircraft observations and observations based on the NEXRAD turbulence detection algorithm (NTDA). They are then ranked by evaluating the forecasted EDR with observed EDR information (e.g. computing probabilities of detection of turbulence above and below turbulence thresholds). Finally, the best preforming diagnostics are combined into one CIT-diagnosis product.

LLT diagnosis has been updated to make use of distinct log-Weibull and lognormal probability distributions in a statistical remapping technique to accurately represent the behavior of turbulence in the atmospheric boundary layer for daytime and nighttime conditions.

Lastly, GTG CAT and MWT diagnosis products have been recalibrated to the HRRR model. Case study results of the upgraded GTG capability based on the HRRR model will be shown.

This research is in part in response to requirements and funding by the Federal Aviation Administration (FAA). The views expressed are those of the authors and do not necessarily represent the official policy or position of the FAA.