Posting what I told you via PM...
Sunny Day (weakest weather in battles though)
- boosts fire moves by 1.5x
- weakens water moves to 50% damage
- Thunder has 50% accuracy
- Solarbeam requires no chargeup
- Pokemon cannot freeze while the sun is up
- Synthesis, Moonlight, and Morning Sun recover 66.6% of the user's health
- Special abilities like Chlorophyll activate... chlorophyll users double speed in the sun, Leaf Guard Pokemon cannot be status'd in the sun, Flower Gift powers up the Pokemon's and the partner's attack and special defense in double battle, Dry Skin users take 1/8 damage per turn, and so does Solar Power users (although their special attack raises)
Rain Dance (one of the most powerful weathers, best in ubers and UU)
- boosts water moves by 1.5x
- weakens fire moves to 50%
- Thunder gets 100% accurate (ouch! suicide for water pokes!)
- Thunder can hit through Protect sometimes (O_O)
- Solarbeam becomes 60 base power
- Synthesis, Moonlight, and Morning Sun recover 25% of the user's health
- Swift Swim users get double speed in the rain, Rain Dish users recover 1/16 of their health, Dry Skin users get 1/8 of their health, Hydration users become rid of their status in the rain
Sandstorm (best weather in standards)
- All Pokemon not Rock, Ground, or Steel type take 6% damage in the sandstorm
- Pokemon with Sand Veil get 20% more evasion in the sand and take no damage from sandstorm
- Rock Pokemon's special defense get boosted by 50%
- Solarbeam becomes 60 base power
- Synthesis, Moonlight, and Morning Sun recover 25% of the user's health
Hail (pretty cool weather, one of my favorites along with rain)
- All Pokemon not Ice type take 6% damage in the sandstorm
- Blizzard gets 100% accurate
- Blizzard can hit through Protect sometimes (O_O)
- Pokemon with Snow Cloak ability gets + 20% in Evasion and not get damaged by hail (although all Snow Cloak Pokemon ARE Ice types)
- Solarbeam becomes 60 base power
- Synthesis, Moonlight, and Morning Sun recover 25% of the user's health
- Pokemon with Ice Body regain 1/16 of their health in hail