I think we'll eventually get a fix from Ken, and I'm not using the stock index page from the template (meaning I can't test it out). If you want to investigate and try things out, the file is wxindex.php (probably renamed to index.php on your site). You want the code that looks like this:
<td align="center">
<img src="https://icons.wunderground.com/data/640x480/<?php echo $SITE['WUregion']; ?>_vi_anim.gif" alt="Regional Visible Satellite"
width="320" height="240" style="margin: 0px; padding: 0px; border: none" />
</td>
It's the "src=" value you need to replace, from the "https" to the ".gif" inclusive. Leave the quotation marks.
To find the image you want, go to:
https://www.wunderground.com/maps/satellite/regional-visiblescroll down to the big map, and select a region that works for you. You may need to scroll down to the image again after the selection. If you want an animated image, click the Play Animation button.
Now you just need to get the URL of that image. Most browsers let you do this with a right-click (might need to use ctrl-click on a Mac) and select "Copy Image Location" (Firefox - exact phrase may differ in other browsers). You can then paste that url between the quotes in the above code. E.g.,
<td align="center">
<img src="https://s.w-x.co/staticmaps/wu/wu/satvs1200_cur/usrow/20190312/1530z.gif" alt="Regional Visible Satellite"
width="320" height="240" style="margin: 0px; padding: 0px; border: none" />
</td>
That's the Roswell, NM view, taken totally by random.
You may need to play around with the image width/height to make it work (looks like the raw image is 1200px wide by 875px high).