The command +today (see +HELP +TODAY) tells you what the current IC weather is. We’re using the Weather & Time system created by Keran (but with quite a lot of modifications done by us), and we feel that this package does a good job of simulating an interesting weather system.
You are not required to obey +today’s weather slavishly, although there’s usually less reason for playing it as being a different weather than a different time. And if you enter a public scene it is always wise to ask whether time is being played according to +today or if something else has been agreed upon.