You probably have a SVG renderer in memory already, and you already have a frame buffer and/or compositor buffer(s). Why should adding a graphical representation of the weather require more than a few KiB?
Because a big picture looks pretty sometimes?
Not sure what you think "having an SVG renderer in memory" means exactly, typically the way an SVG renderer works is that you give it a huge chunk of memory and ask it to draw pixel data there from the SVG file. So even though the SVG is small on disk, rendering a 1000x1000 image from an SVG is gonna need a 1000x1000x3 byte pixel buffer (assuming no transparency or HDR shenanigans)
In a composited window system (i.e., any Mac since Mac OS X and Windows since Vista [I think]), rendering from an SVG would have to occur in a window buffer owned by the application, so it wouldn't save any appreciable amount of memory, assuming the buffer is the size of the window. The days of having an application draw directly into the framebuffer are well in the past.