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First thing: I don't know if it's the right stack to ask this question, so I'm sorry if it's not.

I'm writing an adventure for an apocalyptic RPG session. One point of the plot is a detonation of 100 kt nuclear device in Salt Lake City. At that moment I want my players to be somewhere along the Lincoln Highway (80) in the roadside motel/bar/gas station. This place don't have to exist in real life but I want to place it in realistic location for such enterprise. I was thinking about the junction with road 65 (Google maps shows Mountain Dell Golf Course nearby if you want to see where it is. I'm not from US so I don't know if the numbers of the roads give the exact position). I want my players to be aware of the explosion as soon as it happens but they will probably not be able to see the mushroom cloud because of the mountains. I plant the nuke to be W-76 which is 100 kt, that will give us a 1km high mushroom cloud, but the mountains between the highway and SLC are taller. My question is: what signs of the detonation could be seen/heard? Maybe they should learn about the detonation form some other source? Or maybe I should change the location of the motel? My goal is for them to be aware of the incident and to stay put for at least 30-60 min until the next plot point unravels.

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  • $\begingroup$ It's more of a plot point than a world building question. $\endgroup$ – puppetsock Feb 28 at 22:04
  • $\begingroup$ To confirm it is nuclear blast check for double flash. $\endgroup$ – user6760 Feb 28 at 23:57
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According to the ever-useful NUKEMAP, the mushroom cloud for a 100kT surface blast will reach up to nearly 12000m altitude. Unless you just up Everest and dumped it on top of the mountains east of SLC, the top of the cloud will be visible. I suspect enough of it could be seen to clearly show its mushroomy nature, too.

I can't find any good sources on the strength of the earth tremors that a nuclear blast would cause, but I'm pretty certain they'll be able to feel it. According to some stuff by the USGS, really big bombs will cause proper earthquakes, but more modest ones like this might only be magnitude 3 or 4 at the distance of your observers. They'll probably be able to hear it too, though I have even less idea what that will be like.

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  • $\begingroup$ Yes, just saw an error in my math as you post the answer. I didn't know that NUKEMAP can show the size of the cloud. Thank you :) $\endgroup$ – DontWantMyPlayersToFindMe Feb 28 at 21:22
  • $\begingroup$ @DontWantMyPlayersToFindMe np. Its a shame they don't also have the ground tremor and other effects simulated in the way that the Earth Impact Effects Calculator does, but I guess we can't have it all! $\endgroup$ – Starfish Prime Feb 28 at 21:28
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    $\begingroup$ If I'm reading the NUKEMAP correctly, and understanding where you have placed your heroes... They are at roughly double (maybe a little more) the "unprotected humans killed instantly by heat" radius. At that radius, the flash of the explosion will light up the inside of a closed room through a couple inches of drywall. All unhardened electronics will cease to function. And a few 10s of seconds later they will definitely hear the explosion. Your players will definitely be aware something big happened. $\endgroup$ – puppetsock Feb 28 at 22:03
  • $\begingroup$ @puppetsock I think you're possibly looking in the wrong place. The Mountain Dell Golf Course mentioned by the OP is some way east of ground zero... there's a pair of big lakes out that way. They're well over 10km away from the bomb, and behind a fairly substantial ridge, too. $\endgroup$ – Starfish Prime Feb 28 at 22:28

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