There is a mod already released to address the issue you described, and it is the mod I use personally. It works fine up to AL.
Go to
Simwardrobe and click on Sims 2 to the left. Choose Fixes and scroll down a bit to select Seasons Fixes.
The name of the mod is No Reacting To Rain or Snow. This mod will stop the Sims from stopping what they're doing to react to either rain or snow.
Mr Squinge may not be able to do this as he already has a lot on his plate at the moment. Thread will now be closed. If you have any question or have another request, feel free to open a thread in either the Mod Help or Mod Request Sections.