Modèle:

GFS (Global Forecast System) Global Model from the "National Centers for Environmental Prediction" (NCEP)

Mise à jour:
4 times per day, from 3:30, 09:30, 15:30 and 21:30 UTC
Greenwich Mean Time:
12:00 UTC = 13:00 CET
Résolution:
0.25° x 0.25°
Paramètre:
CAPE and vertical velocity at 700 hPa
Description:
The Convectively Available Potential Energy (CAPE) map - updated every 6 hours - shows the modelled convectively available potential energy. CAPE represents the amount of buoyant energy (J/kg) available to accelerate a parcel vertically, or the amount of work a parcel does on the environment. The higher the CAPE value, the more energy available to foster storm growth. The potential energy can be converted to kinetic energy reflected in upward motion.
It should be remembered that CAPE represents potential energy, and will only be used should a parcel be lifted to the level of free convection. When values are above 3500 j/kg and storms do develop, they may build rapidly and quickly become severe. Often these storms are referred to as "explosive storms" by chasers and professionals. In a high CAPE environment storms that develop can usually be seen by the human eye as rising rapidly. Higher CAPE typically involves stronger storms with a higher chance of large hail and other severe weather. Note that CAPE is usually of lesser importance than the vertical shear environment for tornadoes. The probability of large hail increases with CAPE, given at least moderate shear(values around 500-1000 J/kg are sufficient).
CAPE is very sensitive to small differences in the moisture and temperature profiles. While the maps indicate 1000 J/kg CAPE at some location, a skew-T thermodynamic diagram at that location may indicate 500-1500 J/kg. (Source: The Lightning Wizard)
Table 1: Characteristic values for CAPE
CAPE value Convective potential
0 Stable
0-1000 Marginally Unstable
1000-2500 Moderately Unstable
2500-3500 Very Unstable
3500 + Extremely Unstable
GFS:
The Global Forecast System (GFS) is a global numerical weather prediction computer model run by NOAA. This mathematical model is run four times a day and produces forecasts up to 16 days in advance, but with decreasing spatial and temporal resolution over time it is widely accepted that beyond 7 days the forecast is very general and not very accurate.

The resolution of the model horizontally, it divides the surface of the earth into 20 kilometre grid squares; vertically, it divides the atmosphere into 64 layers and temporally, it produces a forecast for every 3rd hour for the first 240 hours, after that they are produced for every 12th hour.
NWP:
La prévision numérique du temps (PNT) est une application de la météorologie et de l'informatique. Elle repose sur le choix d'équations mathématiques offrant une proche approximation du comportement de l'atmosphère réelle. Ces équations sont ensuite résolues, à l'aide d'un ordinateur, pour obtenir une simulation accélérée des états futurs de l'atmosphère. Le logiciel mettant en œuvre cette simulation est appelé un modèle de prévision numérique du temps.


Prévision numérique du temps. (2009, décembre 12). Wikipédia, l'encyclopédie libre. Page consultée le 20:48, février 9, 2010 à partir de http://fr.wikipedia.org/w/index.php?title=Pr%C3%A9vision_num%C3%A9rique_du_temps&oldid=47652746.