Great! There are a lot of ways to skin this cat but the basics are that you want to query for weather conditions on the Gateway, and store the results as something that the Client can read (most likely as tags).
It just so happens that in our Module SDK there is an example of how to write an OPC driver that fetches the weather from Yahoo weather. This would certainly work, but is overkill (downloading the SDK, compiling the example into a *.modl, getting the module signed, etc is a bit of work.)
I would approach it this way: write a python script that runs as a Gateway timer script that fetches the weather and simply writes it to some Memory tags you’ve set up. Conveniently, there is an example of what this script might look like in the User Manual