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The Weather Prediction Center

Experimental Gálvez-Davison Index (GDI)
using operational GFS Model Output
GFS Initialization 00z 06z 12z 18z
1. North America x x x x
1.1. South Eastern USA x x x x
1.2. Mexico and Southwestern USA x x x x
1.3. Caribbean and Central America x x x x
2. South America x x x x
2.1. Tropical South America x x x x
3. Africa x x x x
GDI Preliminary Manuscript
Updated on October 25, 2016

Figure 1. GDI values and associated convective regimes. See below for more details.

What is the GDI?
The GDI is a stability index developed for tropical and subtropical locations in which (1)subsidence inversions and (2)stabilizing/destabilizing effects of upper ridges/troughs play an important role in modulating convective development. Although the GDI works well across most of the Tropical and Subtropical Americas, it works best across (1)the Caribbean Basin/Southeastern USA and (2)eastern South America south into the Rio de la Plata. For a general guide on index values and expected convective regime please refer to Figure 1 and Table 1.
This website contains realtime 7-day GFS forecasts of the GDI for six domains that cover North America and South America. These are found here . If you would like to code the GDI, you can find a PDF with the calculation algorithm here . Although a complete manuscript is still under construction, there are detailed presentations in PPT that you can download in the following links: (a) English Version Part I , (b) English Version Part II , (c) Spanish Version Part I , (d) Spanish Version Part II . There is also a recorded presentation given at the Media Center of WPC during March 11, 2014, which is available via this link . If you are using Wingridds and would like to install the GDI, we have a complete package with the required files and detailed instructions on how to install it. This package is available here . For any additional questions or feedback please email us at or
Table 1. Interpretation of GDI values. This is a general table that must be adjusted 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.

Calculation algorithm
If you would like to code the GDI, you can find a PDF documentation of the calculation algorithm here .

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Page last modified: Tuesday, 25-Oct-2016 13:01:38 UTC