This is the source of the large archive of images already uploaded by Noaabot. The images hosted by this site are produced by the Weather Prediction Center, itself under the National Oceanic and Atmospheric Administration. As a U.S. federal agency, all works published by NOAA are automatically public domain.
For past examples, refer to https://commons.wikimedia.org/wiki/Category:NOAA_maps. Most currently uploaded images are small, though the weekly pdf summaries can be around 25MB a time.
I am raising this request as part of updating Noaabot's old but working scripts to Pywikibot-core, now http API access is being phased out.