Pokemon Go added a new feature to the game, called a “dynamic weather”. This new weather system has many new effects, which include boosted attack strength, increased spawns of types depending on the weather, and extra Stardust for catching the specific Pokemon.
These Pokemon have increased IVs, a secret thing that determines the power of the Pokemon. At this point in the game, we know that seven types of weather are in the game, Clear, Rain, Snow, Wind, Partly Cloudy, Overcast and Fog, but the favorite one is Partly Cloudy.
This type of weather increases the spawn rates of the Normal Type Pokemon, which is basically most of the Pokemon. This is the most loved weather because of the potential for the player to increase their Stardust number.
When a non-evolved Pokemon is caught, the player gets 100 Stardust, which is used to power up the Pokemon, together with candies. With the new feature, the weather boost gives out extra 25 Stardust.
Also a bonus, with the Partly Cloudy weather, the spawn rate of a high-level Eeevee with high IVs is bigger. These can evolve into Vaporeon or Espeon, two of the most powerful Pokemon in Pokemon Go.