Once enter on this biome, put a X countdown you decide how long is, every time they do an action related to pass the biome, crit: down 2 the cd, sucess: down 1 CD, failure: see Calm before the storm

When party enters biome, put a x(half of pass the biome recommended) countdown, on a failure pc roll, down 1 the cd when it reach 0 something reach the party (storm, fire, blizzard, anything you find optimal)
Optional can be enemies or dangers coming

When storm start, put a 2xPC countdown, every hope player gains can be expend on reduce 1 CD, when reach 0, Storm stop, you decide if theres another coming, while on storm, all rolls are doing on disadvantage or every failure make a stress, or difficulty get plus 1xtier (what you think fills better)
Optional you can do this event do damage to players (xd8+1, where X is tier), if that the case, i recommend to reduce calm before the storm counter, but apply damage only one time per storm trigger.
Also if you make it enemies or danger, activate a encounter

The difficult of this environment is 8 + (3xtier)

spend 2 fear to start a encounter , then you can spend up to 0-1-3 more fear to make it easy, balanced, of harder encounter, select adversary related with the biome
Optional it can be a xd8 damage or half on a reaction roll

Party can do 1 tag team roll, on sucess, they find a safe place in the middle of the biome (oasis, small isle, etc), they can short rest there or recover 1d4 stress