>>36541235A Pokemon found in the wild while it's type aligns with the current weather condition, its CP will likely be higher than the it would be with no weather influence. Fans refer to this as the "weather boost" as it allows them to find Pokemon that don't need to be powered up as much.
Obviously, some weather conditions are rarer than others depending on the area. My local raid community is going nuts right now because the birds are back, they can be shiny, and Florence is giving them all a nice weather boost.