Offset Type     Name             Description
------ -------- ---------------- ------------------------------
 0000  BYTE     cmd
 0001  BYTE     type
 0002  BYTE     num              (number of weather effects on screen)
 0003  BYTE     temperature

Type:

  0x00 - "It starts to rain"
  0x01 - "A fierce storm approaches."
  0x02 - "It begins to snow"
  0x03 - "A storm is brewing.",
  0xFE - (no effect?? Set temperature?)
  0xFF - None (turns off sound effects), 

Notes:

• Temperature has no effect at present.
• maximum number of weather effects on screen is 70.
• If it is raining, you can add snow by setting the num to the num of rain currently going, plus the number of snow you want.
• Weather messages are only displayed when weather starts.
• Weather will end automatically after 6 minutes without any weather change packets.
• You can totally end weather (to display a new message) by teleporting. I think it's either the 0x78 or 0x20 messages that reset it, though I haven't checked to be sure (other possibilities, 0x4F or 0x4E)
• To display snow and rain, send a rain packet first and then send a snow packet with the number of effects equal to the number sent in the rain packet plus the number of snow effects to add.