Castform Weather
The weather may change randomly every hour. The weather can fluctuate quickly, but also keep for a while as it is. Each Castform icon in the userbar represents the weather on the game, and for each specific weather, a specific type of Pokemon will gain 50% more EXP. This does not affect eggs.
If you hover over the Castform Icon on-game, it will say what Pokemon type will gain 50% more EXP. You can also click on the icon to obtain the Weather Forecast of the day.
Obtaining Weather Castforms
Castform Weather forms were released and obtainable as Pokemon on 25/06/14.
Using a special Weather balloon on one of your Castform's will make it evolve, depending on the current weather in Emera Town.
Weather Balloons can be found rarely on rumble missions.
Castform Weather Icons
Clear Sky - There is not a single cloud over Emera Town and the sun is shining bright. However, a slight breeze is blowing from the seaside and you shouldn't go outside without a jacket. (All Normal Pokémon gain 50% more EXP.)
Rainy - Better take an umbrella. (All Water Pokémon gain 50% more EXP.)
Cold - That's cold! (All Steel Pokémon gain 50% more EXP.)
Hail - Watch out for hailstones! (All Ice Pokémon gain 50% more EXP.)
Strong earthquakes - WARNING: There will be powerful earthquakes from time to time. Better stay at home! (All Ground Pokémon gain 50% more EXP.)
Very Sunny - Don't stay too long in the sun! (All Fire Pokémon gain 50% more EXP.)
Meteorites - SPECIAL WARNING: A dangerous meteor swarm is expected today and experts say that they will land near the town. Don't be scared when a loud bang wakes you up. It's probably just a meteor. (All Dragon Pokémon gain 50% more EXP.)
Gusty - That's gusty! I might get blown away! (All Fighting Pokémon gain 50% more EXP.)
Mystic Aurora - ... W-What is this Aurora? Look, it's amazing! (All Psychic Pokémon gain 50% more EXP.)
Thunderstorm - Wow, lightning! (All Electric Pokémon gain 50% more EXP.)
Windy - It's currently windy in Emera Town, but it's a pleasent breeze due to the hot shining sun. However, it's still recommended to wear a jacket when going outside, so you don't catch a cold. (All Flying Pokémon gain 50% more EXP.)
Sunny - Oh, I like sun! Just like my plants do. (All Grass Pokémon gain 50% more EXP.)
Small earthquakes - You can expect short earthquakes from time to time in Emera Town, but experts say that they're neither strong nor dangerous for all inhabitants. (All Rock Pokémon gain 50% more EXP.)
Muggy - Man, it's muggy today. (All Bug Pokémon gain 50% more EXP.)
Very foggy - I can no longer see my hands in front of my face! (All Dark Pokémon gain 50% more EXP.)
Smog - Is it sunny? Cloudy? Foggy? I can't really tell since there's a large cloud of smog currently over Emera Town, coming from the big city. (All Poison Pokémon gain 50% more EXP.)
Foggy - The fog is blocking my view... (All Ghost Pokémon gain 50% more EXP.)
Rainbow - Look, there's a beautiful rainbow in the sky over Emera Town! Oh no, wait, there are actually two! What a rare, amazing occurrence. (All Fairy Pokémon gain 50% more EXP.)
Weather Forecast
This is a new feature created on 3/Feb/2015, which allows users to be aware of future weather conditions.
The page states the current server time and the current weather (with an image of the current Castform as well as a short description and its effects). There is also a table shows the next 3 consecutive Castform, with the name and period they will appear later.
In addition to that, you can also check the moon phase to see when the Full Moon Island and New Moon Island will be accessable.