Mud Rain: Rain containing particles of sand or dust. These particles may originate in very distant regions. Source: European Union.
This has been documented since ancient times.
African Sahara dust storms whip up clouds of sand and they go to high altitudes. Then when the clouds mix up and make friends with the other clouds (particularly the wet ones) the wind moves it all over the Mediterranean, and splat- we get mud rain. (OK. I didn't major in Geography in school.)
Every year we experience it and every year we are totally surprised at how much mud actually comes down!
Ironically, we've always felt that rain was something that rinsed mud OFF the car... this rain really took a perfectly clean car and made a mess of it!
As it came early this year I won't worry about washing the windows quite yet. There's still another couple of months of rain to speculate over.