IPA: /ɔːˈtʌmnəli/
KK: /ɔːˈtʌmnəli/
In a way that relates to or resembles the season of autumn, often characterized by falling leaves and cooler weather.
The trees changed color autumnally, creating a beautiful landscape.
Autumnally is formed from "autumn" (from Latin *autumnus*, meaning the season of harvest) and "-ally" (meaning in a manner relating to). The word describes something that is characteristic of or occurring in the autumn season.
Think of the word 'autumn' which refers to the harvest season, and remember that 'autumnally' means in a manner relating to that season.