i use whether spell quite often. but as they said you can not successfully use a spell if it gos against the natural weather of what ever season it is.
but is also helps to know the scientific function of what ever whether you wish to manipulate.
for example if you wish it to rain during the summer or spring you would need to pout your intent in to what conditions you wish to attract rain. for rain requires a sudden Chang in temperature in combination with low anaphoric pressure, with what ever directional wind that will blow the clouds to your area or what ever area you wish to attract rain to. rain also require a body of water like a lake, ocean, river, or pond. so you would also need that to succeed in attracting rain to what ever area you wish to attract rain to.