CalendarAgent wants to connect to wunderground 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
Weather Underground is the provider for Apple's weather data in OS X/macOS (and iOS). Calendar.app downloads weather information for calendar events with a set location.
As soon as you add a location to a calendar event Calendar.app will try to fetch the weather conditions if it's only a few days in the future.

Location services (System Preferences &gt; Security &gt; Privacy) does not effect the download of weather information.