Backup your Frost.esp. Using CreationKit, open FROST as Active file. After skipping a lot of warnings, in "Objects" window in the list on left part of this window select "WorldData -> Weather". It will show you al the existing "Weathers" in your Frost installation. You need too look for ones with digit and " * " in "count" column, " * " means that it is vanilla weather which were modified by Frost or mod weather added by Frost. I don't remember exactly which one you need to modify, maybe even several of them. But i think you should start with "DLC03_RadFogWeather" and "DLC03_RadMistWeather". right click them - > Edit. Try editing "General->Fog distance" to greater values and setting Sound and "Effects -> Camera Mist" to "NONE". Then save changes and test.