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Domain 8. Southeast South America
Graphics use 1° GFS Model Output


Terrain elevation in meters above sea level. Source: GFS0.25°(NOMADS-NOAA).

ALGORITHM GFS 00Z GFS 12Z
Enhanced GDI and Flow - EGDI.CMD
The Enhanced GDI (EGDI) is an enhanced version of the Galvez-Davison Index (GDI) that adds the detrimental effects of low relative humidity in the 300-400 hPa layer (also proxy for elevated inversions), the detrimental effects of upper convergence, the enhancing/detrimental effects of low-level moisture convergence/divergence, and a precipitable water enhancement factor. As the GDI, it helps to identify environments favorable for shallow convection, deep convection or deep convection with the potential for heavy rainfall. Loops include the low-level (1000-850hPa) and upper level (400-200hPa) flow to account for dynamic and orographic forcing, and movement of systems. It also plots 950-700 hPa convergence/divergence of the flux of mixing ratio, upper divergence (400-200hPa), and GDI advection and flux.
 
 
Potential for severity and hail (Trial) - GR02T.CMD
GR02T highlights regions with the potential for severe convection in shades of colors. Light gray, green, red and fuscia generally relate to marginal, low, moderate and elevated risk for severe convection. If the shades match red/fuscia boxes encircled by red/fuscia contours, the risk for hail increases. GR02T is a modified version of the GR02 algorithm designed to detect the potential for hail in South America (Galvez and Santayana, 2019).
How does GR02T determine a potential for severity?
Environments suitable for deep moist convection are first defined by considering precipitable water, negative Lifted Index, and mid-level rising omegas, high relative humidity and cool air. Inside these 'deep moist convection' regions, the potential for severity is enhanced by 700-500 Lapse Rates > 16°C, 500 hPa temperatures<-8°C, Lifted <-3°C, enhanced 0-3km and 0-6km shear, enhanced 400-200 hPa divergence, enhanced 950-700 hPa moisture convergence and 500-300 hPa omegas.
 
 

Note: These algorithms are only forecast tools, not official forecasts. For information on the algorithms, click on the red text.

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Page last modified: Wednesday, 19-Feb-2020 17:38:21 UTC