Sandstorm in Riyadh

I was in work this afternoon (Saturday starts the week here in Saudi) and I turned to look out of the window of my office which is in downtown Riyadh and suddenly the day had turned to night. In the space of less than five minutes a sandstorm had swept in and visibility on the road outside was 50m at most. In twelve years in the Gulf I've never seen a sandstorm like it.

Here's a photo from my phone.