Seems like you are talking about weather underground station, unfortunately it is not supported by rachio directly.
What you can do is sign up for weather underground api here (link). It will default to a free stratus developer plan. This is the one you want. (when asked how you wish to use it, you can specify “website” and pwsweather.com for the website address).
Next you can set up a free pwsweather.com station, this is somewhat similar to weather underground, just make sure you specify location coordinates which you can than find via rachio, they have a handy tool to do this via address.
You can then make up a custom URL for use with wufyi.com, it will look something like this
This custom URL will now transfer the latest data point from weather underground to pwsweather each time URL is requested.
Finally can automate this process to run every five minutes or so via cron-job.org (use custom wufyi URL when setting up the cron-job).
If you do all this, you will soon see your pwsweather station available to your rachio. Whole process should take about 10 minutes and has a benefit of being free.