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The Weather Prediction Center

The Gálvez-Davison Index (GDI)

     The GDI (preliminary PDF), is a thermodynamic index developed by the WPC International Desks in 2014, to improve the forecasts of tropical convection, particularly in trade wind regimes. It is a diagnostic tool that considers low and mid-tropospheric moisture, but emphasizes (1) the stabilizing effects of mid-tropospheric ridges and (2) the stabilizing and drying effects of trade wind inversions. Real time GDI forecasts, using GFS data, are available in the following table.

Current experimental forecasts with GFS data
00Z 06Z 12Z 18Z
1. North America
 
 
 
 
   1.1. Southern and eastern US
 
 
 
 
   1.2. Mexico and the south western US
 
 
 
 
   1.3. Caribbean and Central America
 
 
 
 
2. South America
 
 
 
 
   2.1. Tropical South America
 
 
 
 
3. Africa
 
 
 
 
4. Asia and the Maritime Continent
 
 
 
 
5. Pacific Basin
 
 
 
 

              Table with loops using flash instead of html5 here.

Interpretation
     The higher the GDI, the larger the potential for deep convection. Very large GDI suggests potential for heavy rainfall. Table 1 presents general guidelines for index value interpretation. Yet, note that GDI skill and thresholds for types of convection vary spatially and seasonally. Also, note that the GDI is a diagnostic tool, thus its skill will depend on the database used for its calculation. Finally, combine the GDI with an analysis of atmospheric dynamics for better forecasts, as the GDI helps to describe the environment for tropical and subtropical convection, but does not necessarily relate to regions of dynamically-induced ascent or descent.
     More details on the GDI and how to code it are available on the preliminary manuscript and on Powepoint presentations available in English ( part I and part II ); and in Spanish ( part I , and part II ). A presentation recorded on March 11, 2014, is also available . For any questions or feedback please email us at michel.davison@noaa.gov or jose.galvez@noaa.gov.

Table 1. Correspondence between GDI values and expected type of convection. This is a table for general reference. We recommend adjustments upon location and season.


GDI for Wingridds
If you have Wingridds running in your computer, you can implement the GDI by downloading this package . Instructions on installation are included in the package.



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Page last modified: Friday, 06-Apr-2018 18:16:34 UTC