Okay, so I want to run this adventure (A dark and stormy knight) for my group.  It's wonderfully atmospheric, and I really don't care that it's a bit heavy-handed in framing people into the scene and situation.  That's cool.

BUT ...

I want it to make sense.  I want to be able to feel that there's a world ticking along by sensible rules.  And there's this one bit that ... I can't get it to make sense.  Specifically:

• The PCs are forced into shelter by a raging electrical storm with hail and stuff.  The GM is encouraged to have this storm dealing lethal damage if necessary to force the players into the ante-room of the tomb.  That's cool, like I said, heavy-handed framing is no bad thing for a quick scenario.
  
• There are some bug-bears to encounter halfway in the tomb, but of course they couldn't have survived that long because they'd have starved to death.  The scenario author adds a light-well from the top of the hill in which the tomb is embedded, and a swinging rope hints (possibly even before the attack) that the bug-bears are tomb-robbers who descended from above.
• But ... but ... there's lethal hail and killer lightning above.  They're going to pick the worst possible weather, ever, to go out and raid a tomb?  Even if they could do it, why would they?  Why not wait for better weather?

I know, I know ... they're random monsters with a thin veneer over them ... and I don't think my players will ever question, they'll just kill the brutish beasts.

But it's throwing me.  It genuinely is.  Hearing some effort to make sense of the ecology and causality (a local giant-spider has preyed upon the rat population that attacked the PCs earlier, for instance) makes it hard for me to just suspend disbelief.  Does anyone have a recommendation for a sensible way to have these bug-bears in this locale?

I mean, to give you an idea of how whacked my ideas for this stuff are, I'm contemplating having the bug-bears join the party (under Storm-Peace) in the ante-chamber, and then maybe be uneasy collaborators in the early investigation of the ruins, before breaking the storm-peace at some crucial moment (unless the PCs break it first, of course).

I think that might be fun, but ... clearly not the intent of the original module.  If there's an easier way to make everything make sense, I'm all ears.

Could it be as easy that the bugbears themselves were forced into the chamber because of the weather, knowing that it was a safehouse of sorts for these kinds of storms?  They also could use this location as a safehouse of sorts, to loot travellers that are caught in the storms if they happen regularly enough.  Maybe have some sort of shaman.

Hrm ... how to get that across?  I could have some figures at the top of the hill, clambering about in the early stages of the storm.  The PCs see them, wonder if "Hey, I wonder if they're going the same place" and then when they first hit the antechamber they say "Nope, nothing to do with us ..."

Then, when they see the light-well, and the rope later, they can say "So what would be up above ... oh shit!"

>nod, nod<  That could work!  Cool.

I actually ran a scenario like this a while back; the players immediately assumed that the baddies (in this case, hobgoblins) were some sort of storm worshippers.
I like leaving some incongruities in the game, and seeing how the players explain them; it usually works pretty well if most of the game has explainable details.

(IIRC it was hobgoblins, only the zombie was a bugbear)

When I ran it, the bugbear was a legendary champion from the past, and the hobgoblins were there specifically to bring him back to life to fight for them.  The ritual to bring him back had to be performed during one of the storms in order to work.

Like the cleric situation, I think you might be worrying too much.

You could replace the Bug Bears with a similar CR creature that makes sense in the context, or a trap/puzzle of the same CR.