You will need:

A sprig of broom
Sea salt
Water
Wooden spoon
A red candle

Now, for this spell you need a piece of the broom plant, NOT an actual broom you sweep with. You may have to check herb suppliers, florists or plants shops to find it. There really isn't a substitute for broom in a weather spell.

Light the red candle and pour water into the bowl while you say:

Rain that brings a land's rebirth
Time to weep upon the earth.

Use the spoon to stir up the water, then dip the piece of broom in. Repeat:

Winds shall follow, you shall see
Blowing wildly through the tree

Envision a storm growing in strength and power. Let a few drops of hot wax from the candle fall into the water, and say:

Lightning quick, lightning long
Make it last, make it strong

Add in the salt to seal the spell and stir again. Give it one last stir, and take it immediately outside and toss it all into the air (you can hold on to the bowl). Don't let the water settle down before you throw it. Now you can expect a storm to start brewing on the horizon within a few days.