A weather widget using 8 bit color plus alpha on a 4k display show three full size images in 100mb. But I suspect that's not the ux we're talking about here, and a widget style system has no excuse.
https://wttr.in/ shows it's very possible.
Use an svg.
Or render everything using css, 100mb is someone not trying. 1gb is absurd abuse that only domestic violence victims put up with.
Apple's Weather app has an animated background, glassy views, and nice animations like water droplets on the glassy views when it's raining. So rendering all that on a 4k or more display at 10bit depth is going to consume a bit of RAM. However I guess it can surely be improved to make it consume less RAM.