Weather

Weather is an in-game phenomenon that mimics a Trainer's real-world weather experience. The current weather is reflected in the Map View and capture phase. Weather conditions make Pokémon of certain types to: Attacks of boosted types are more effective in Gym and Raid Battles, even if the user is not those types.
 * appear more frequently in wild
 * be at least level 6 and IV floor of 4/4/4 in wild
 * be level 25 and 13 in the Bonus Challenge of Raid Battle and Team GO Rocket respectively
 * award 1.25x Stardust when captured

Types of weather
There are eight types of weather conditions that occur in-game.

Sunny/Clear
This weather condition is referred to as Sunny during the day and Clear at night.

Boosted types:  Fire Grass Ground Full weather images: 

Partly Cloudy
Boosted types:  Normal Rock Full weather images: 

Overcast
Boosted types:  Fairy Fighting Poison Full weather images: 

Windy
Boosted types:  Dragon Flying Psychic Full weather images: 

Rain
Boosted types:  Bug Electric Water Full weather images: 

Fog
Boosted types:  Dark Ghost Full weather images: 

Snow
Boosted types:  Ice Steel Full weather images: 

Extreme
If the weather outside is too dangerous, the game will issue a severe weather alert to notify the Trainer that they should seek shelter.

Full weather image: 

Weather Icons


Trivia

 * This feature was announced along with Pokémon from Hoenn region on December, 2017, and released two days later.
 * Several weather conditions like Rain, Wind or Snow causes respective visual effects in Pokémon encounter screen.
 * The Snow weather condition never appears in places where it never snows for obvious reasons.
 * Pokémon boosted by weather conditions appear with additional spinning, pale-blue rings beneath them in the Map View when they spawn.
 * That ring overrides the pink ring beneath lured Pokémon.
 * The same Pokémon spawn's CP level and IV will be updated as the weather changes. If the Trainer enters encounter screen before weather changes, the Pokémon will have originally spawned stats even if they are caught after weather changes.
 * This is possibly bugged for the once-per-day person Pokémon spawn, which seems to have its CP change according to weather, but reverts to original when caught.
 * Before the release of the Sinnoh Pokémon, weather had a higher effect on the rate at which Pokémon appeared.
 * The weather attack bonus can be stacked with shadow bonus.