Rain

Sit down and start to meditate until you are in a comfortable state. When you feel you are ready, chant;

'Rain, rain let it rain,
Rain for me today,
Pour down, pour I say,
Let sunshine lack just for today
Let the rain not fade away
So mote it be
By the power of three'

Repeat this three times, or a multiple of three times. If it does not work immediately, that's ok, sometimes it just needs some time to work depending on how hot or cold it is where you are doing the spell.