Weather is a new feature with version 2.7 - we are looking forward to your feedback

You can add the weather forecast via the plus-button in the calendar list (MENU - manage calendars). 

You can switch between °C and °F with the metric switch in the 3-dots menu of the weather entry in the calendar list.

aCalendar uses Visual Crossing as weather provider.

For 2023 aCalendar weather is in a free beta phase. Future availability and pricing will depend on usage and feedback during the beta phase. Like always in Google Play, you will not be charged anything without explicitly confirming a purchase.