Weather on site?

Question

css

The site has a dark horizontal bar (You can see an example in the header of this site, where the "Ask a Question" button is located)

It is used to indicate the theme of the page.

I would like to make a weather display, degrees, and a background like rain / wind / sun, preferably with animation, instead of her background.

The algorithm is this:

1. Check if the page has loaded completely (so as not to interfere with loading);
   
2. We send an Ajax request to the service and get the weather forecast according to the region of the request.
   
3. We save it in a cookie and issue a period (for example, 2 hours)
   
4. We change the background and numbers in accordance with the weather.
   
5. As soon as the cookies expire, we repeat the algorithm.
   

The site is visited only by users from Russia and the CIS.
1. Tell me the services that provide api weather for free and restrictions?
2. Tell me where you can download weather backgrounds / pictures (I would like modern ones)?
And share your experience and pitfalls of the services you use.