Disclaimer and Labeling
GTG is generated operationally at the National Weather Service's Aviation Weather Center, which is supported 24 hours a day,
7 days a week. Its use is unrestricted (meteorologists, dispatchers,
GA and commercial pilots, ATC, etc.)
as a supplementary source of weather information.
Overview
The Turbulence page contains GTG-2, which depicts mid-level
and upper-level CAT from 10,000 feet to FL 450,
with 0, 1, 2, 3, 6, 9, and 12 hour forecasts. It does not provide turbulence analyses or forecasts below 10,000 ft
MSL. GTG-2 is a Supplementary
Weather Product. A Supplementary Weather Product is an aviation weather product that may be used for enhanced situational
awareness. If utilized, a supplementary weather product must only be used in conjunction with one or more primary weather
product (
AIM 7-1-3).
The GTG-2 graphics are computer-generated four-dimensional
forecasts of information related to the likelihood of encountering CAT
associated with upper-level fronts and jet streams, and is not intended to predict turbulence associated with convection
and thunderstorm clouds or breaking mountain waves. The product provides forecasts for the 48 contiguous United States, much of
Canada and Mexico, and their respective coastal waters at flight altitudes from 10,000 MSL to
FL450 only, that is, it does not provide forecasts from the surface to 10,000 ft. Users should
also be aware that turbulence is a highly dynamic phenomenon and in case of rapidly changing conditions the product may not
accurately convey a significant hazard.
GTG-2 graphics may be used as a higher-resolution
supplement to AIRMETs and SIGMETs,
but not as a substitute for the turbulence information they provide. GTG-2
graphics are authorized for use as an unrestricted, supplementary weather product. The
GTG-2 does not have the capability to be amended.
See the definition of primary and supplementary weather products below.
The GTG-2 product consists of a 00, 01, 02, and 03 hour forecast,
which are updated every hour, and a 06, 09, and 12 hour forecast, which are updated every three hours, starting at 00Z.
GTG-2 graphics are "snapshot" graphics,
intended to depict forecasted clear air turbulence conditions at the valid time (for example, at 1200Z), not for a valid
time range (for example, from 1200Z to 1300Z). The GTG-2
graphics suite is automatically produced with no human modifications. Information on the graphics is determined from observational data,
pilot weather reports, upper air soundings, satellite soundings, automated aircraft reports, and surface weather reports,
all of which are integrated with computer model output.
Due to the use of computer model output, the GTG-2
product issuance times are reliant upon the timing and resolution of the released underlying weather model data.
GTG-2 uses 00, 01, 02, 03, 06, 09, and 12 hour forecast
fields from the RUC model with a horizontal grid spacing of 20 km and 50 vertical levels.
The RUC updates hourly, and the total processing time is dependent upon the amount of data
in that update cycle. Due to the processing time of the model data, the GTG-2
will normally be released 50 minutes after the valid time of the RUC data set. The longest
update cycles occur at 00Z and 12Z due to additional data ingest and processing.
GTG-2 will normally be released 100 minutes after the
valid time of the RUC data set at 00Z and 12Z. ADDS is configured so the composite
graphic with the most relevant valid time should display when you initially select the
GTG-2 product, but all graphics in the
GTG-2 suite are available for viewing via the valid
time and altitude selection interface.
Note: Users should pay close attention to the valid time of individual graphics due to the delay caused by
RUC update cycles required for the
GTG-2.