Pokémon GO Weather Boost Chart.
Which weather boosts which types, and what a boost does to the level, IVs and CP of the Pokémon you catch.
1.2x move damage · 1.25x catch Stardust
Which weather boosts which types
Boosting weather for every type
What a weather boost changes
Why boosted catches are worth chasing
Weather in Pokémon GO follows the real forecast where you play, and each of the seven conditions boosts two or three types. A boosted wild Pokémon gets five extra levels, so it can spawn as high as 35 instead of 30, and its IVs can't drop below 4. That saves the Stardust you would have spent powering it those five levels.
Raids work the same way: the boss is caught at level 25 rather than 20 when the weather boosts one of its types, which is why raid groups quote two 100% CPs for every boss. In battle, any move of a boosted type deals 1.2x damage, for the boss as well as for you.
Dual types count once. A Pokémon is boosted if either of its types is, so Dragonite is boosted in windy weather by both of its types and nowhere else.