I have making a new town mod , this town made in one indoor cell as exterior cell.

I want my new npc talk about weather in dialouge, and make it in cs, make dialouge for each the weather number 1.2.3......

I found it don't work when my town rain.

Have you looked at how it is handled in tribunal?

There are some dialogue greetings based on the weather machine which has a script attached which depending on the weather sets the global Mournweather

Tribunal keeps track of it using journal entries on the associated quest (though there may be a global variable as well, but I don't think so).

When you set your interior cell to behave as an exterior, you select a region for the cell to mimic. The trick then is use getcurrentweather in a script, then you can set a (global most likely) variable to show what the weather type is and use that as a dialogue filter. At least that's the only way I know to do it without MWSE or MGE.

if i had to take a guess id say that you just tell the NPC to look at whatever cell you told the interior cell to get its weather from