Can I know the day-time, biome, and weather of a block / chunk from code?

world.getWorldTime

world.getBiomeForBlockCoordinates

world.isRaining

And can someone clarify what biome.rainfall returns?

And what is the range of that function?

And can someone clarify what biome.rainfall returns?

And what is the range of that function?

 

It's the effective humidity of the biome.  Deserts are dry, jungles are wet.

 

The canonical range is 0 to 1, but is technically unbounded.  I've gone in an fiddled with levers and made the nether biomes negative and pushed the wet biomes up as high as 2 with no undo effects (technically speaking, there is a clamp on the values--between 0 and 1, I think--for when it uses them to get grass and leaf colors).

 

I would roughly approximate the rainfall value as "that value + 1" in inches of rain per month, ignoring the Minecraftian "the entire world has the same weather state" effect.  It's not entirely accurate, but its the translation I've used for my own mod, and no one has a good concept of how much rain their Real World location gets every month anyway.

 

Temperature, by the way, roughly approximates 0.1°MCU (Minecraft Units) = 10°F.  Freezing weather in Minecraft is right at 0.2°MCU which is pretty darn close to the Fahrenheit scale, although some biomes (cough, desert, cough) are artificially high or low so that the grass color matches the desired hue.  Temperature canonically ranges from -0.5 to 2.  Again, they're clamped for rendering the color, but I haven't figured out how.  0-2, I assume, but there might be some value transformation prior to that to account for the preternaturally cold regions with negative temps.