First, please note that to display an animated GIF image as a camera, your Blue Iris must be version 126.96.36.199 or above. Images here are from Blue Iris 5.
The method below is used to determine the URL for an animated 'PNG' of the desired weather radar loop on Intellicast as follows:
1) Go to this URL: Intellicast - Current Radar in your browser
2) Go to the dropdown menu to the left under 'Region' and select the desired region to be displayed.
3) Toward the right, click on 'Play Animation'.
4a) In IE, right-click on the image and select inspect element to see the URL. You are looking for something like this https://s.w-x.co/staticmaps/wu/wxtype/county_loc/sat/animate.png
4b) In Chrome, just right-click and select copy image address.
5) In Blue Iris, create a new camera configured as in the images below using the URL for the PNG file obtained above.
Note it does not visibly affect the load on the server either.
You might also want to look at Trafficview cams though most of the feeds in my area were down when I checked. There may also be feeds from your local DOT, like this one for Texas. You might also find some feeds by searching for the town or highway name like these for Cedar Park.