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AWC Home > Testbed > GTG > FYI/Help
Graphical Turbulence Guidance (GTG) Help       

GTG Overview

The Graphical Turbulence Guidance (GTG) is an automatically-generated turbulence product that predicts the location and intensity of turbulence over the continental United States (CONUS). The GTG was developed by the NCAR Turbulence Product Development Team, sponsored by the Federal Aviation Administration's Aviation Weather Research Program, and implemented by the National Weather Service Aviation Weather Center as a supplement to turbulence AIRMETs and SIGMETs.

The GTG ingests the full resolution 20 km hybrid B RUC model, domestic pilot reports (including those received directly from Northwest Airlines) , and one-minute lightning data. The GTG uses this data to produce an upper-level clear air turbulence (CAT) prediction.

The algorithm uses a "fuzzy logic" computational scheme which assigns a weighting function to 11 operationally used, and tested turbulence forecasting tools. The 11 indices that GTG currently weighs in this scheme are: Brown-2, Colson Panofsky, ETI1, Richardson Number, TKE-KH, Endlich, NGM1, Shear, Vort2, Divergence, and Temperature Gradient.

A turbulence diagnostic is computed from numerical weather prediction output (i.e. RUC2) at the assimilation time. The algorithm then maps each of the diagnostics to a common turbulence intensity scale (0-1) where the thresholds are defined as :

GTG Intensity Scale

Category Numerical
Representation
None 0
Light Greater Than 0.125 - 0.375
Moderate Greater Than 0.375 - 0.625
Severe Greater Than 0.625 - 0.875
Extreme Greater Than 0.875

The diagnostic values are then compared to other available observations (PIREPs) within a time window around the assimilation time, and above some altitude cutoff (20,000 feet). The skill scores are then combined with the weights to get the GTG forecast. The weights are then subsequently used to produce the 3, 6, 9, & 12 hour GTG forecasts.

Web Page Navigation

The GTG web interface can be accessed from the small image entitled 'GTG Product'  on the AWC home page:

https://aviationweather.gov

By clicking this link, the user will be directed to a GTG page that contains moderate or greater turbulence data.  The GTG web page is divided into four different pages. The user has the option of viewing the GTG forecast for light or greater intensity, moderate or greater intensity, severe or greater intensity, and extreme or greater intensity. The colors within the color bar (located at the bottom of the image) are active links to allow the user to navigate through these different images.

Navigation Table

To the right of the forecast image, there is a table which has all of the available flight levels on the vertical axis and the valid forecast time on the horizontal axis. The button color corresponds to a given forecast period:  

00 hour forecast   03 hour forecast   06 hour forecast   09 hour forecast   12 hour forecast 



When a given button is moused over, the correlating flight level and forecast time each highlight, letting the user know what he or she is currently looking at.

A desired image may be held in place by clicking once on the corresponding button.  The user can then mouse over other images while holding one in place.

Overlays

Additional information can be placed on top of the GTG turbulence data. Valid turbulence AIRMETs and SIGMETs can be displayed above the turbulence data by either mousing over or clicking on the buttons entitled 'AIRMETs' and 'SIGMETs'.

Clearing The Image

The Clear Button can be clicked to clear all of the current overlays and turbulence data off of the topographic background map.

"00" Hour Forecast Updates

Every 3 hours (at 00Z, 03Z, 06Z, 09Z, 12Z, 15Z, 18Z, & 21Z) GTG processes forecasts out to 12 hours ( HH+00, HH+03, HH+06, HH+09 & HH+12 ). In addition, a "00" hour forecast is processed every hour and is reflected in the "00" column on the page.

White Background vs. Terrain Background

Some users may prefer to have a terrain map as a background for the GTG and some users may prefer to have a white background. By clicking on the       'terr map' link, the user will be taken to the same exact GTG page, only with a colored terrain background map instead of a white map. Users who prefer one over the other may bookmark that page for future use.

Printing an Image

By double clicking one of colored buttons, a new window will pop up, allowing the user to make a print out of the GTG data.  The background will always be white on the printouts, and the title, NWS disclaimer, and turbulence data will be able to be printed.

National Weather Service Disclaimer

The GTG gif images displayed on the AWC  web page are all official products of the National Weather Service. On the top of each gif image, there is a short disclaimer, in red text, which describes who should use this product to make scientific decisions about the state of the atmosphere. The disclaimer reads as follows:

"The GTG is an automatically generated turbulence forecast product that supplements AIRMETs and SIGMETs by identifying areas of turbulence. The GTG is not a substitute for turbulence information contained in AIRMETs and SIGMETs. It is authorized for operational use by meteorologists and dispatchers only."


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Page last modified: December 16, 2011
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