For the latest GK Weather 1.8 module you need to get an App ID, Client ID (Consumer Key) and a Client Secret (Consumer Secret) codes from Yahoo.

Go to: https://developer.yahoo.com and create an account or log in to your existing account if you have one.
When you are logged into your account click on the “Create an App” button. You may be redirected to the main Yahoo information page when you log in, if this is the case input “developer yahoo” into the search box and select the search term to get to your account.
On the Create Application page, input an “Application Name”, e.g. GK Weather.
Make sure the "Application Type" radio button is selected as “Web Application”
You can ignore the Description (Optional), Home Page URL (Optional) and Callback Domain (Optional), as these are not required.
Click on the “Create App” button at the bottom of the page.
After a few moments your App ID, Client ID (Consumer Key) and a Client Secret (Consumer Secret) codes are generated.
Input the generated codes into the Basic Settings area of the GK Weather Module in the back end of your website, for example: Yahoo App ID = App ID, Consume Key = Client ID (Consumer Key) and Consume Secret = Client Secret (Consumer Secret)
Under the Layout section area of the GK Weather module in the back end of your website, you can select icons from the “Iconset” field for your preferred weather symbol display. Under the General Settings section, your WOEID can remain unchanged.
Save your settings and view the module in the front end.