What it says in the title

>Water Veil
Now also buffs SpDef in Rain

>Hyper Cutter
Adds +1 to all Attack boosts as well as protecting from attack drops (Hone Claws now looking scary)

>Big Pecks
Now also increases the power of wind-based moves, because the only Pokémon with this ability are birds who I'm assuming have pretty strong pectoral muscles aka they can flap pretty hard

>Magma Armor
Becomes more like Water Bubble. Protects from freeze and now also reduces damage from ice and water moves. May also add an effect where it makes fire move stronger, but that doesn't really seem to fit the theming of this ability.

>Forecast
When this Pokémon switches in it will automatically activate this ability regardless of the weather IF it is carrying a weather rock or knows a weather causing move. If either condition is Matt, this ability will activate and then cause a particular weather to occur based on either this pokémon's held item (which weather rock it has) or which weather move is in its first move slot (or closest to the first move slot), with the weather rock taking precedence over the move slot. Also gives this Pokémon a passive 20% buff to speed and special attack as long as there is active weather