Weather is that stuff outside. It's visible in the verbose description of the room, or if you look at the sky.
There are several aspects to it.
Type and severity of weather
These are the messages you get in order from windless to as windy as you can get:
- no wind at all
- almost no wind
- a gentle breeze
- a steady breeze
- a strong breeze
- a steady wind
- gusty winds
- strong winds
- gale-force winds
- storm-force winds
These are the messages you get in order from cloudless to as cloudy as you can get:
- a beautifully clear sky
- a few high level cirrus clouds
- scattered puffy clouds
- some puffy clouds
- many puffy clouds
- medium cloud cover
- dense cloud cover
- packed cloud cover
- thick black clouds
- thick heavy storm clouds
Looking at the clouds while outside gives you the room's full weather line.
The precipitation part combines the following like so:
Precipitation types depend on temperature, from coldest to warmest they are:
Precipitation strength can be from the weakest to the strongest:
- very heavy (if rain: torrential)
You can look at the precipitation by type, i.e. look rain, but if it's sleeting you can only look at sleet not rain.
Doing so will give slightly different messages:
- steadily (if there is a steady wind or stronger: hard)
- very heavily (if rain: torrentially)
With extreme rain and wind, you additionally see:
Peals of thunder and streaks of lightning rend the sky.
Or if visibility is bad, you'll only see:
Peals of thunder echo overhead.
Effects of precipitation
If it's snowing, raining, or sleeting, visibility will be worse, meaning that the map will be more limited than if the weather were clear. The heavier the precipitation, the smaller the map gets--very heavy snow (for example) can make it impossible to see out of the room.
Being out in it make you wet.
Making things from snow
If it's snowing, or if you're in a room with snow on the ground such as the ice land (such rooms mention snow in the long description of the room), you can make things out of snow.
Most notably, you can make snowballs, which can then be thrown at others or yourself.
However, there's a wide range of other things you can make--these become temporary features in the room, remaining there until they melt (a process taking several minutes).