Hey all, here's a quick tutorial to modify weather chances.  It's the same process in FO4 and Skyrim/SSE.

• Load xEdit (SSEEdit / FO4Edit)
• Make sure there are no conflicts with True Storms and other mods (look up how to resolve conflicts and patches in xEdit, I won't cover that here)
• Look for REGION records.  In each one, under Weather Types, you'll see records for each weather that can be in that region. The values are:
  Weather (the weather ID)
  Chance (the... chance!)
  Global (always null)
• All you need to do is edit the chances but make sure all values should total 100.  For example: Clear 25, Cloudy 25, Fog 25, Rain 25 = 100.
• It's a good idea to update the Climate records as well, as these are fallback when there is no region data.