I have tried to make this as easy as possible without adding a ton more work for any of us. I wanted to use authentic year calendars from the Time and Date site, but I'd have had to manually create the weather for each day. My second choice has been to screenshot past year calendars from Weather Underground and put them into a custom block on our main site index. Later, I will try to have them display in our timeline page and at the top of a page when we create a thread. For now, this will have to do.

NO ONE needs to try to go back and add weather information into your past or current in-progress threads unless you just want to. 

Here is a screenshot of our main index with the block showing.

As it says, click on the thumbnail to get an enlarged view of the image.

For whatever day you choose, it shows the weather and phase of the moon for that day.

Hope this helps and is somewhat along the lines of what was wanted.