A Simple Dust Storm

dustStorm.flv 

A quick and easy way to do a dust storm is to use only the textural aspects of a fluid. This scene uses a fluid with no grids, just textures and gradients. The animation was done by animating the position of the fluid along with texture time and offset.
I started with a plain 3D fluid then in the attribute editor set it to the preset "cloudbank", which is a purely textural preset with no grids. Instead of a y gradient I used a center gradient and made the fluid somewhat oblong. Once can scale the fluid with the scale tool but when changing its aspect one should use the size XYZ attributes, setting the resolution XYZ in matching proportion so that the voxels remain square. When one has a fluid with no grids the resolution is still used for two functions: shaded hardware display and in the rendering determines the number of steps marching through the grid. Thus if you make the resolution very low you may need to increase the shading quality attribute to compensate.

From there it was a lot of tweaking of texture frequency and ratio as well as getting the shadowing right. A single spotlight with raytrace shadows was used(one needs to use raytrace shadows for cast shadows from a fluid). Cast shadows was enabled on for the fluid shape to get shadows on the ground. The opacity required to get sharp boundaries on the dust resulted in strong self shadows, due to the lack of secondary light scattering on the fluid. Lowering the shadow transparency helps this but also makes the ground shadows too soft. So I set incandescence high on the fluid and the color dark so that the self shadowing was not too strong. Both color and incandescence have y gradient ramps that make the dust light at the top and darker at the bottom.
The animation is a translation of the fluid combined with a slow animation of texture time and offset.

TIP:  A convenient way to animation an attribute like textureTime is to type into the numeric edit box to the right of the attribute in the attribute editor:

= time * x

where x is a number determining how fast you want the animation. For example if x was 10 then after 1 second the attribute value would be 10.

For the sky I kept the background black and created a 3d fluid and set its preset to "sky fog" then played with the color and incandescence. The volumeSamplesOverride helps to integrate the two fluids, which does not work as well in this case for Mental Ray so the Maya renderer was used.
If one wishes the dust to collide or have dynamics then make the density+velocity grids dynamic, set opacity input to density and use an oval shaped emitter with dropoff to match the centergradient effect (other emitter setups may also work well). One would also generally need to do an extend on the fluid to have it cover a larger area, to allow room for the emitted density to move into. To push the fluid one could apply a volume axis field with a directional motion blowing inward along the right hand boundary. Generally avoid applying unbounded forces across the entire fluid as these tend to build up over time as well as fight the dynamic incompressible flow of the fluid. Also with such a setup it will help to make the fluid boundaries open at the right and left to create a wind tunnel effect. The animation on texture offset should then also be either disabled or reversed in direction, moving with the wind flow but not quite as fast.

Here is the Maya scene file:
 dustStorm.ma