WXSIM is a very unique software package - over 25 years in the making - for modeling, forecasting, or simply studying weather. It is perhaps best described as an "interactive local atmospheric model". You initialize it with current data, some optionally downloaded from the internet, and then "turn it loose" to model the weather for the next few days, but with the option to interact with the program and mix in some of your own forecasting skill and knowledge.
Recently, many users - mainly owners of home weather stations - have been using WXSIM to automatically generate forecasts which can be (using other programs) uploaded to web sites. For some examples, click here for examples of WXSIM forecasts on the internet.
A vast amount of work has gone into the development of WXSIM. Space does not allow a full discussion of all the program's algorithms, but just to provide a notion of what is involved, here are some of the variables modeled or used by the program:
Date, time, sun angle, distance from sun, latitude, longitude, elevation, proximity
to large bodies of water, climatological temperature and dew point data, heat
capacity of the surface, latent heat of condensation, incoming shortwave solar
radiation, outgoing longwave terrestrial radiation, cloud albedo and emissivity,
mixing due to winds and convection, advection of temperature and dew point,
upper level temperatures and dew points (in 5 atmospheric layers), formation
of dew, frost, and fog, formation of sea breezes, accumulation and melting of
snow, and much more.
In addition to the program's main job of modeling/forecasting, it performs a variety of other useful functions, including:
WXSIM occupies a niche filled by no other program. Used properly, its forecasts are of professional quality, often as good as or better than anything else you'll see, especially since customization allows the forecasts to be highly specific for your exact site. Its interactive nature also makes it a great learning tool, either for amatuer weather enthusiasts or meteorology students.