Weather in CalenGoo
You can either just active Google Calendar’s weather calendar (see below) or you can activate CalenGoo’s weather function under "Settings > Weather" to display a weather forecast in CalenGoo. CalenGoo’s day view and some of the agenda widgets have a special way to display the weather: In the day view you can get a three hour forecast at the right side of the screen. And in the agenda widget you can get a forecast in the date header of each day:

In addition CalenGoo can generate simple all-day events from the weather forecast so that you can see them in all calendar views and all widgets (all widgets that display all-day events).
Weather calendar
According to this post and this post Google Calendar does not support a weather calendar any more. But you can use CalenGoo’s weather calendar as explained above.
If you sync that calendar directly (i.e. not via Android) CalenGoo can even display small icons for these events:

Changing Google’s weather calendar from °C to °F or vice versa or changing the location
If you would like to change the weather calendar from °C to °F or vice versa or its location, please sign in to Google Calendar:http://calendar.google.com
Then click the gear icon in the upper right corner and then “Settings”:

There you can choose the location and format for the weather report under the “General” tab:


To make CalenGoo recognize the change immediately (and not on the next day when the weather changes), please first set it to “Do not show weather”. Then sync CalenGoo by choosing “Sync” from the menu. Wait for the sync to finish. Then set it to the desired value “°C” or “°F” and sync CalenGoo again. If the new weather calendar doesn’t appear, please tap “Settings”, “Visibility/Download”, press the menu button and choose “Refresh Android Calendars”.
Alternative weather calendar
It is also possible to subscribe to other weather calendars that provide more information, e.g. “wunderground”:- Search your own city on http://www.wunderground.com
- Move the mouse over the blue button in the upper right corner of the page, and right-click the appearing “Download iCal” menu entry. Choose “Copy Link Address”.
- Add this iCal Link to your Google Calendar using Google Calendar’s “Add by URL” function.