Sand storm weather contains a weather and a SweetFX setting that try to fake a sand storm in Assetto Corsa by modifying the colorCurves.ini and weather.ini files.
Originally created for the Black Cat Country track it also fits well other tracks with desert landscapes, mountains and forests like Nordschleife, Brands Hatch, Bathurst, Spa and even rally ones like Kouvola.
Download, unzip, copy to your Assetto Corsa folder and select the "Sand storm medium" weather. The use of the SweetFX setting is optional but overall it gives a more menacing look.
Here is how it looks in game.
And here is how a real sand storm looks like.