Odd one. Without (knowingly) changing anything (of course SOMETHING must have changed) when I booted up Apple Calendar the other day I got this alert from Little Snitch:
CalendarAgent via com.apple.WeatherKitService.xpc wants to connect to api.wunderground.com on TCP port 443 (https)
Any idea why or how that would happen? I don't sync to any Calendars that I know of, and use the Calendar infrequently.
OS X El Capitan 10.11.6