There is a saying in chazal that 1/3 of all the troubles to befall the world will occur in the war of Gog U'Magog.
Is there any hint/allusion in scripture or midrash of an upcoming nuclear war?
There is a verse in Yoel, which may be familiar from the Hagadda (or from learning Navi), which describes the apocalypse. Yoel 3:3-4 (verse 4 included for context):
Metzudas Dovid (ibid) explains the word timros (תמרות) to mean that the smoke will go straight up like a palm tree (תמר).
My father-in-law (who shall remain nameless) wanted to explain the specific choice of a palm tree as the example of something that goes straight up because it spreads out at the top, and the image of the smoke would be like that of a palm tree - a plume going straight up, then blossoming out at the top. Much like a mushroom cloud.
1If anyone wants to translate it as "the day of the great and awesome Hashem" I am fine with that- as far as I know, the modifier is vague.
The best source for an apocalyptic doomsday event (that I have seen) is from an ancient mystical text Sefer Heichalot (http://en.wikipedia.org/wiki/Hekhalot_literature) 5:4-5 and 6:1-2 which is cited by Rabenu Bechaya in Bereishis 44:17 (page 349 Chavel edition)
Among other fascinating and (mind-blowing) novel ideas he writes (translation mine):