Model:

Arpège(Action de Recherche Petite Echelle Grande Echelle) from Meteo France

Updated:
4 times per day, from 08:00, 14:00, 20:00, and 00:00 UTC
Greenwich Mean Time:
12:00 UTC = 12:00 GMT
Resolution:
0.1° x 0.1° (Europe)
0.5° x 0.5°
Parameter:
Fog Stability Index
Description:
This is a stability index for fog formation. It is from 2WW/TN-79/008, "A New Technique for Forecasting the Occurence of Fog and Low Stratus Ceiling by Use of a Flow Chart".
The equation for the index is:
Fog Stability Index = 2*(ts - t850 + ts - tds ) + W850 =
=4ts - 2(t850 + tds) + W850
Fog risk (FSI)
high
middle
low
FSI < 31
31 < FSI < 55
FSI > 55
Arpège:
Arpège
ARPEGE uses a set of primitive equations with a triangular spectral truncation on the horizontal, with a variable horizontal resolution, with a finite elements representation on the vertical and a “sigma-pressure” hybrid vertical coordinate. It also utilizes a temporal two time level semi-implicit semi-lagrangian scheme. The horizontal resolution of the ARPEGE model is around 7.5km over France and 37km over the Antipodes. It has 105 vertical levels, with the first level at 10m above the surface and an upper level at around 70km. Its time step is of 360 seconds.
NWP:
Numerical weather prediction uses current weather conditions as input into mathematical models of the atmosphere to predict the weather. Although the first efforts to accomplish this were done in the 1920s, it wasn't until the advent of the computer and computer simulation that it was feasible to do in real-time. Manipulating the huge datasets and performing the complex calculations necessary to do this on a resolution fine enough to make the results useful requires the use of some of the most powerful supercomputers in the world. A number of forecast models, both global and regional in scale, are run to help create forecasts for nations worldwide. Use of model ensemble forecasts helps to define the forecast uncertainty and extend weather forecasting farther into the future than would otherwise be possible.

Wikipedia, Numerical weather prediction, http://en.wikipedia.org/wiki/Numerical_weather_prediction(as of Feb. 9, 2010, 20:50 UTC).