Model:

Times Series from the GFS Ensemble

Updated:
2 times per day, from 10:00 and 23:00 UTC
Greenwich Mean Time:
12:00 UTC = 13:00 CET
Resolution:
1.0° x 1.0°
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
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).