WordPress.org

1. Download
2. Change the config variables in the "EDIT THIS" section (You may want to use the weather icons, in which case you should upload them to your server as well.)
3. Upload this plugin to your wp-plugins/ directory
4. Active the GetWeather Plugin via the admin menu
5. Place this code in your template:

Or get much more fancy and include:

You need only change the "citycode" (the first variable in the function) to your own city. You may use a US zip code in place of a standard city code. International users will have to use a standard city code.