Can you turn weather off in Minecraft?

To toggle off weather type in /gamerule doWeatherCycle false

If you simply want to enable a particular weather cycle for a near infinite amount of time, you can use the command /weather type time, for example if you want to have clear weather for a year, you could use /weather clear 9999999999

This might be a little late, but.. I always use the command /time set 14000 (it's a default command). This command makes it completely dark, so you can use a bed. Most of the time the rain/snow is over when it's morning.

With zombe's modpack, you can control weather. ;)

If there is bad weather happening at night, a bed should help.