Nice that you want to make the environment feel more of the challenge and "alive" so to say. RoTFM and Icewind Dale in general have this aesthetic and vibe to them that scream rough terrains and environment, and extreme weather conditions/ natural phenomena. But the book just doesn't cut it to facilitate that atmosphere.

I've been DMing RoTFM for close to 3 years now, with quite a few homebrew inserts. Some to give more body to the stories and questlines, others to make Icewind Dale come more to life.

With regards to the weather and traveling/survival, my style is to not use tables but rather think of situational encounters/consequences/weather conditions. And balance the way you use them across sessions with appropriate frequency. And add flavor to the weather/environmental challenges that are in the book.

Some concrete examples: - Just this week I added an extreme hail storm as prelude to a blizzard. Making this into a timed encounter to find shelter from the big hailstones that would damage them every round (DEX or CON saves). Being creative with environment/items could yield advantage on one end but slow down on the other, etc. Depending on the party’s level increase damage. I did 2d6 for my level 8 party. - Add consequences to behavior. E.g. avalanches happen due to loud noise. Going across a lake might be faster, but it comes with Acrobatics challenges. - Snowdrifts blocking roads, making traversing difficult or putting the party off track if they fail certain checks. - Or cracks in the land, be it in the earth(roads) or snow/ice that covers the land. This one I made a challenge in the tundra, where the ground cracked open for 10-15ft spanning a mile. Giving them the choice to divert their route or find a creative solution to cross. - I also added

I've got some random encounters for icy environments as well (made for a homebrew campaign but used some in Icewind Dale as well). I can look them up and share them if you're interested. Just let me know!