The Met Office said it began detecting the phenomenon in England yesterday and suggested it could arrive in Scotland today.
Forecaster Luke Miall explained: "For weeks, high pressure has been sitting over the top of Europe, drawing southerly winds across the country.
“This has given us the recent hot weather but it has also picked up Saharan dust and it is heading towards the UK.
“It only comes to the ground when we get showers and we’ve had a few inquiries in England today when this has happened.
“Scotland can expect some downpours on Wednesday night, so it’s possible that’s when you will begin to see it settle on cars and windows.”
Yesterday saw some brief outbreaks of rain north of the border. One motorist on the south of Glasgow couldn’t work out why his car was still dirty after washing it.
He said: "I was just drying it off when there were spots of rain. As soon as I tried to dry it, more dirty marks emerged.
“Eventually, I just gave up.”
Wheelie bins, too, were showing signs of what is often called ‘Blood Rain.’
The French departments of Brittany and Normandy have been placed on ‘orange’ alert for pollution, due to a combination of the Saharan dust and local car emissions.
Drivers in Brittany have been told to reduce their speed by 20km per hour and outdoor sporting events have been restricted for those with pre-existing health issues.
In Cornwall, the Kernow Weather Team said:” Dusty air blown 2,000 plus miles from the Sahara is on it way to Cornwall and the Isles of Scilly by Tuesday”.
Scotland set new temperature records on three successive days over Easter, culminating in a reading of 24.2C (75F) at Kinlochewe in Wester Ross on Easter Monday.