Control of the elements is limited somewhat by the laws of nature. You cannot make it snow in the middle of the summer. The Wiccan Rede (and its instruction to do whatever you please as long as it harms no one) prevents you from causing natural disasters like tornados or floods. The threefold repayment you would receive from such an action would not be something you would want to deal with. But that doesn't mean you can't have some influence on the elements.

The best weather alteration spells are the subtle ones. Bring on a light rain or keep one from falling on you. Bring enough snow for a snow day (but not a blizzard). The best part of these spells is that they require no supplies. You only have to walk outside, raise your hands towards the sky and say things aloud. For that reason, you should probably choose a secluded area so that crowds of people don't gather to look at the crazy person yelling at the clouds.

Note: There are spells that exist to manipulate fire, but it is strongly discouraged that a novice experiment with them. The risk of something going wrong is far too great. People and property could be seriously damaged or destroyed. It is best left to experienced spell casters or covens.

Bring Rain

Stand outside, lift your palms toward the sky and say aloud:

The ancient Gods and Goddesses,
I invoke thee.
The water from the sky,
Let it be.
I command you now,
To you all.
Listen to my desires
And let rain fall!

Prevent the Rain

When the sky begins to get cloudy and dark, walk outside and lift your hands towards the sky. Say the following aloud:

Gods and Goddesses of power,
Gods and Goddesses of might.
I bid thee now,
Stop this plight.
Stop this rain-
We do not need more.
Let it fall nevermore.

The rain will move on to another location before it falls.

Snow Day Spell (call for a good deal of snow)

Magic can't make it snow in the middle of the summer. It can't supercede the laws of nature. But if the weather is already cold but not enough snow has fallen to get you a day off of work or school, stand outside, palms to the sky and chant the following three times:

Work thy will, Goddess Hecate,
I am calling upon thee
To let the snow fall
In piles so tall.
Snowed in shall I be,
Bring this to me.

Create a Breeze

Stand outside, raise your hands to the sky and chant the following aloud:

The Gods and Goddesses of the sky,
I call upon the elements of the air
To bring the winds and blow in here
So it may be.

Bring on the Sun

Stand outside, raise your hands to the sky and chant the following aloud:

Goddess Sol, bless and decree
Allow the sun to shine on me.
I call on the element of the sun
So that I may leave and have some fun.