Weather is a game mechanic reflecting atmospheric conditions that affects Pokémon attack values of certain types. It changes every four hours and certain weather conditions can only occur in specific Regions. Weather also restricts the evolution and in-route availability of certain Pokémon.
The table below is accurate as of version 0.6.8.
Clear The weather is clear and pleasant.
Overcast Clouds fill the skies.
Rain It's rainy and humid.
Thunderstorm It's currently raining heavily with thunder.
Water x1.1, Electric x1.1
Sunny The sunlight is strong.
Fire x1.1, Grass x1.1
Snow It's cold and snowing.
Hail It's cold and hailing.
Blizzard A howling blizzard blows.
Ice x1.2, Fire x0.9, Grass x0.9
Sandstorm A sandstorm is raging.
Rock x1.1, Ground x1.1, Steel x1.1
Fog The fog is deep...
Windy Mysterious strong winds blow.
Flying x1.2, Dragon x1.1
Pokémon affected by weather
Cherrim (sunshine) Sunny
Goodra Rain, Fog
Weather-dependent route encounters
Castform Clear, Overcast, Sandstorm, or Windy
Castform (sunny) Sunny
Castform (rainy) Rain or Thunderstorm
Castform (snowy) Snow, Blizzard, Hail, or Fog