Blood Rain

I am putting this one in the “learn something new everyday” category. And just in time for Halloween…

(Posted on BBC News online.)
Weird weather is predicted in the UK this week and could include “blood rain.” What is it?

If current weather forecasts turn out to be right, the weather will be a very mixed bag in the UK this week. Unseasonably warm temperatures reaching 20C (68F) are predicted, followed by rain and possibly snow – and all over the next few days. There is also a possibility of something called “blood rain” in the South East, but what is it?

“Blood rain” a term used for rain carrying sand from deserts. When the rain falls it looks a reddish colour and when it dries off it leaves a thin layer of dust which can also be red, hence the name. It is capable of coating houses, cars and garden furniture. “It is a rather grandiose term for fine desert sand particles that are whipped up by winds and mix with the moisture in clouds,” says a Met Office spokesman.

Storms in the Sahara desert, which is around 2,000 miles away, are usually responsible for stirring up dust blown towards the UK, say weather experts. The current winds arriving in the country are part of the band of warm air which is predicted to bring unseasonably warm temperatures over the next few days, followed by rain in some areas. The rain and the fine layer of dust left after it falls can also be other colours. “The different coloured sands in the Sahara mean the rain and the coating it leaves can vary in colour,” says weather expert Philip Eden. “It can be reddish, but it is quite rare. It is more likely to be a sandy colour or brown. It’s not as spectacular as it sounds.”

“Blood rain” happens a few times a year in the UK, say experts. It is more common in southern Europe like Spain and the South of France, which are closer to the Sahara. But it can travel longer distances and fall in areas like Scandinavia.

For “blood rain” to leave a residue it needs to be a brief shower. “This is because there is a higher concentration of sand in a short shower,” says Eden. “Heavier, more prolonged rainfall simply ends up washing away the residue.”

There are very early recordings of “blood rain” in historical texts. It is mentioned in Homer’s Iliad, thought to have been written in the 8th Century BC. The 12th Century writer Geoffrey of Monmouth, who made popular the legends of King Arthur, also referred to it.