5th Gen Inb4 New Weather Type.

[Karel_Kazuki]

Weathereffects could be/are as follows:
Rain-water
Sandstorm-GroundRock Steel Types are unaffected/boosted
Hail(Which I believe counts as snow)-Ice
Drought/Sunny Day-Fire Boost,Grass Boost?(forgot) Solarbeam 1 turn etc.
Fog-Accuracy Decrease
Acid Rain-poison boost,(Health is dropped or Poisoned pokemon
Typhoon/High Wind-Flying Types boosted while everything other than those plus rock ground steel are unaffected by it
Eclipse(which does sound good)-Dark, Ghost and Psychic types boosted)
Red Sky(Dragon Type Boost)
Forest Grace(Bug and Grass Boosted)
Greatness Unlocked(lost train of thought xD) Normal and Fighting Boosted
Clouds( or new Rain Dance effect)Electric Boost

 

[OmegaRuby and AlphaSapphire]

Weathereffects could be/are as follows:
Rain-water
Sandstorm-Ground Rock Steel Types are unaffected/boosted
Hail(Which I believe counts as snow)-Ice
Drought/Sunny Day-Fire Boost,Grass Boost?(forgot) Solarbeam 1 turn etc.
Fog-Accuracy Decrease
Acid Rain-poison boost,(Health is dropped or Poisoned pokemon
Typhoon/High Wind-Flying Types boosted while everything other than those plus rock ground steel are unaffected by it
Eclipse(which does sound good)-Dark, Ghost and Psychic types boosted)
Red Sky(Dragon Type Boost)
Forest Grace(Bug and Grass Boosted)
Greatness Unlocked(lost train of thought xD) Normal and Fighting Boosted
Clouds( or new Rain Dance effect)Electric Boost

I like these Ideas, though the Greatness unlocked doesn't sound much like a weather thing but still like your ideas :D!

 

[Karel_Kazuki]

Lol I couldn't think of a Weather effect for Normal and Fighting so i just had to say something and not leave them out xD

 

[OmegaRuby and AlphaSapphire]

What about "great Clear sky" for Normal and Fighting types :P

 

[Gymnotide]

Repost for compilation

Magnet Storm | Electric | -- POW | -- ACC | 5 PP
Effect: Summons a strong magnetic field that amplifies Electric moves.

+50% to Electric-type moves.
All Pokemon lose 50% Evasion.
All Pokemon except Electric and Ground-types lose 6.25% HP per turn.
Weather Ball becomes Electric-type.

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I'm also really hoping this happens too:

Overcast | Dark | -- POW | -- ACC | 5 PP
Effect: Causes thick fog to appear on the battlefield.

The Accuracy of moves is lowered by 10%.
Weather Ball becomes Flying-type.
Moonlight, Morning Sun, and Synthesis only heal 25% HP.
Solarbeam requires 2 turns to charge.
Fire-type moves are weakened by 25%.
Water and Electric-type moves are strengthened by 25%.

Defog | Flying | 60 POW | 100 ACC | 10 PP
Effect: Clears the battlefield of weather-effects, Mist, Safeguard, Light Screen, and Reflect. This attack only does damage if an effect is removed. Lowers the foe's Evasion by 1 stage.

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Pollute | Poison | -- POW | -- ACC | 5 PP
Effect: Makes the weather turn acidic, damaging non-Poison-types each turn.

Inflicts 6.25% damage each turn to all types (including Steel), except Poison-types.
Pokemon with Water Absorb, Rain Dish and Storm Drain take 12.5% instead.
Pokemon with abilities making them immune to effect damage / Poisoning are immune (Magic Guard, Leaf Guard, Immunity, etc.).
Pokemon with Poison Heal are healed instead for the same amount.
Lowers the Defense of all Pokemon except Poison-types by 1 stage.
Solarbeam takes 2 turns to charge.
Moonlight and Morning Sun heal only 25%.
Synthesis fails upon activation.
Weather Ball becomes Poison-type.

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Pitch Veil | Dark | -- POW | -- ACC | 5 PP
Effect: Eclipses the sun or moon, casting a great shadow on the land.

Special attacks have their Accuracy treated as though the Pokemon had their Accuracy lowered by 1 Stage.
Ghost and Dark-type attacks never miss.
Recovery effects are halved.
Morning Sun, Moonlight, and Synthesis all fail upon activation.
Solarbeam fails upon activation.
Flash lowers the foe's Accuracy by 2 Stages and will never fail to hit.
Night Shade is strengthened by 50%.
Weather Ball becomes Dark-type.

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As for Typhoon... That makes zero sense at all, since Flying-type Pokemon will be thrown around mercilessly by the wind so they can't fly or use any aerial attacks.