http://newsletters.wwiionline.com/063006.html
"After getting a lot of feedback from last week's sneak preview of the upcoming lighting, cloud and fog changes the dev team put their heads together and decided to take it a step further. The result is the first implementation of in-game weather.
Here's how its planned to work; A series of files are created defining different light and fog levels as well as size, density and altitude of cloud layers. These files will be used by the host to select a new "weather condition" setting for the gameworld. During each night cycle, the host will select a different file than used in the current cycle and pass it to each player's client. The result will be in-game variable weather conditions.
We asked Gophur to clarify a few details of this upcoming feature.
Q. Will the new weather be localized? Will it be cloudy over Antwerp but sunny over Bertrix?
A. No. Currently the weather systems will be theater wide. Localized systems require too many core changes at present to be worthwhile for development.
Q. Will these "weather condition" files be used randomly or will we have a month of dark, dreary days?
A. The initial implementation is random though we are exploring weighted systems as well as forecasting systems.
Q. Are we getting rain and snow with the new weather feature?
A. No. Rain is very difficult largely because you can go inside and outside of buildings. To do rain correctly in an environment like ours would require some collision detection that is too processor intensive given the amount of physics we already run for vehicles and projectiles.
Q. Will any kind of weather forecast be available for planning?
A. We hope so but given the current 6 hour day night cycle in game a 5 day forecast would only be useful for 24 hours planning. This will have little strategic planning impact and player planning will suffer the same uncertainties that real war commanders faced.
Q. How many different types of weather days will there be?
A. Currently there are three and we may expand that to five.
Q. Will any of the weather conditions be so severe that flight operations may be suspended?
A. Suspended no but hampered yes. There will be days where low altitude will be more appealing and days where high altitude will be more appealing.
Q. When can we expect to see this new feature in-game?
A. When 1.24 goes live which should be later this summer."