Modelo:

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

Actualização:
4 times per day, from 3:30, 09:30, 15:30 and 21:30 UTC
Greenwich Mean Time:
12:00 UTC = 12:00 WET
Resolution:
0.5° x 0.5° for forecast time <= 384 hrs
parâmetro:
Cloud cover (low,middle,high,total)
Descrição:
Clouds are vertically divided into three levels: low, middle, and high. Each level is defined by the range of levels at which each type of clouds typically appears.

Level Polar Region Temperate Region Tropical Region
High Clouds 10,000-25,000 ft
(3-8 km)
16,500-40,000 ft
(5-13 km)
20,000-60,000 ft
(6-18 km)
Middle Clouds 6,500-13,000 ft
(2-4 km)
6,500-23,000 ft
(2-7 km)
6,500-25,000 ft
(2-8 km)
Low Clouds Surface-6,500 ft
(0-2 km)
Surface-6,500 ft
(0-2 km)
Surface-6,500 ft
(0-2 km)


The types of clouds are:

High clouds: Cirrus (Ci), Cirrocumulus (Cc), and Cirrostratus (Cs). They are typically thin and white in appearance, but can appear in a magnificent array of colors when the sun is low on the horizon.

Middle clouds: Altocumulus (Ac), Altostratus (As). They are composed primarily of water droplets, however, they can also be composed of ice crystals when temperatures are low enough.

Low clouds: Cumulus (Cu), Stratocumulus (Sc), Stratus (St), and Cumulonimbus (Cb) are low clouds composed of water droplets.
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 model is run in two parts: the first part has a higher resolution and goes out to 180 hours (7 days) in the future, the second part runs from 180 to 384 hours (16 days) at a lower resolution. The resolution of the model varies in each part of the model: horizontally, it divides the surface of the earth into 35 or 70 kilometre grid squares; vertically, it divides the atmosphere into 64 layers and temporally, it produces a forecast for every 3rd hour for the first 180 hours, after that they are produced for every 12th hour.
NWP:
A previsão numérica do tempo usa o estado instantâneo da atmosfera como dados de entrada para modelos matemáticos da atmosfera, com vista à previsão do estado do tempo.
Apesar dos primeiros esforços para conseguir prever o tempo tivessem sido dados na década de 1920, foi apenas com o advento da era dos computadores que foi possível realizá-lo em tempo real. A manipulação de grandes conjuntos de dados e a realização de cálculos complexos para o conseguir com uma resolução suficientemente elevada para produzir resultados úteis requer o uso dos supercomputadores mais potentes do mundo. Um conjunto de modelos de previsão, quer à escala global quer à escala regional, são executados para criar previsões do tempo nacionais. O uso de previsões com modelos semelhantes ("model ensembles") ajuda a definir a incerteza da previsão e estender a previsão do tempo bastante mais no futuro, o que não seria possível conseguir de outro modo.

Contribuidores da Wikipédia, "Previsão numérica do tempo," Wikipédia, a enciclopédia livre, http://pt.wikipedia.org/w/index.php?title=Previs%C3%A3o_num%C3%A9rica_do_tempo&oldid=17351675 (accessed fevereiro 9, 2010).