Have a 2010 Silverado and after being parked at work on a windy day the dash is covered in sand from coming in the defroster,why and how can it be stopped,only vehicle I've had do this,I don't mean dust I mean sand all over.

 

have a cabin air filter installed. a 2010 will have the opening in the hvac box. Its may just need a filter or it may need a filter kit. the kit is for hvac cases that don't have the opening cut out. you cut the outline and install the filter and door that comes with the kit.
remove the glovebox and inspect for a filter door or filter opening that needs to be cut out.