Encounter: Sandstorm

This is another idea I've had for a while that I just kind of like, but I'm not sure that I would ever use. I like when combat includes a random element that affects the environment, but I can see how the dice could make such an encounter completely unwinnable. That in and of itself is not always a bad thing, as the PCs should be challenged with "impossible" situations that they can puzzle their way through. But I think I'd have to refine this a little bit more before I considered it anything more than a half-baked idea I had for such an encounter.


Environment: Desert, Wasteland
Theme: Limited visibility, Difficult terrain

Characteristics:

• Sight range reduced
• Ranged weapons' range reduced
• Movement is in random directions
• Movement is slowed
• Phases of severity

Uses:

• Dramatic confrontation
• Antagonists likely are not impaired
• Hectic battle, where friend and foe are indistinguishable

Info:
Allow me to preface this by saying that sandstorms are also very good skills challenge. However, they're run very similarly to how the forest fire I wrote about earlier is run, so I decided not to just make that same idea happen again. Instead, this is to talk about this kind of disaster during a combat. Mostly this is to make an otherwise straightforward fight very interesting, by manipulating some factors that most fights assume to be givens. If the PCs cannot see their enemy, and can't even control their movement correctly, then a battle can quickly become more involved.
First off, the sandstorm should not be a permanent condition. Rather, it should come and go in phases. If the PCs are caught blind and flat-footed for the entire fight, then it's just flailing about aimlessly in the sand. Instead, every few rounds the sand should blind them completely and cause the PCs to lose their sense of direction. The DM should roll a die to randomly determine when the next wave of sand should come, so the PCs are kept on their toes. This makes it very unpredictable.
The antagonists should all be expecting this kind of sandstorm. Presumably they live in this kind of area, and so are used to the limitations. Perhaps they have trained ground-dwelling desert beasts to ambush the PCs during the fight? Or they have special crossbows designed to fire bolts during a sandstorm, while the PCs only have arrows that get knocked about. At the very least, the enemies should be able to reposition and get into an advantageous position during the sand phases. This provides the PCs with a tactical challenge that may be very difficult to overcome without having planned for such an occurrence.
The goal here is for there to be a large-scale battle in the midst of the storm. The idea that I have in my head right now is for there to be a wall with archers on top, and riders on the ground atop desert-dwelling beasts. The PCs are attempting to assault some sort of fortress, and so have to brave through the arrows while the storm is raging. The melee with the riders would be intense as it is, as most combats are when one group is unmounted and the other is, and the storms only make it that much worse. Should the PCs break through, they enter into a courtyard where they are further surrounded by archers. Only once they battle their way indoors does the storm cease to have any effect. And depending on the type of storm, it could continue to impact the battles; the ceiling caves in and the room begins to fill with sand, sand elementals start attacking the fortress out of the storm, the evil wizard that summoned the storm descends upon the PCs for an impromptu boss battle. The possibilities are endless.