Hey @ally, I recently ran into the same problem like you.
I followed all instructions given to you from @sdetweil and finally figured out, what the problem was: openweathermap updated its api to version 3.0!
Even if you have a free subscription (limiting to 1000 api-calls a day, which is fine unless you stay above a refreshrate of every 3 minutes), you need to edit the link in node_helper.js from
var url = "https://api.openweathermap.org/data/2.5/onecall" +
to
var url = "https://api.openweathermap.org/data/3.0/onecall" +
For the free subscription on API-Version 3.0, you need to provide your credit card information, but you can set the maximum of possible API-calls to 1000, so that you will never ever ran into any costs.