I see these questions on SO -Past Weather forecasts archive and I wonder why these questions are not coming to our site. Are they off topic ?
Definitely on-topic IMHO.
As to why it's on SO rather than here, I would guess that the question has been asked by a programmer who is used to using SO but is unaware of this site's existence.
Given that this person is specifically after APIs rather than human-readable websites I don't know whether they are more likely to get good answers here or there.
I'd say it's certainly on topic here, but might actually do better in a programmer-focused community rather than a meteorology/earth science related community. A fair part of cross-discipline programmers may have interacted with NOAA, people just wanting to make a weather app. Whereas I'm not sure a lot of meteorologists would seem to tend to interact with such a tool, being in research or operations or such. No reason to say it shouldn't be here, I'd appreciate the unified location and added information if nothing else. Always thought there needed to finally be a tool to better cross connect communities (and those search) on such questions.