Met Office weather warning: Blood rain set to strike as thunderstorm alert raised

The phenomenon occurs as a result of red Saharan dust mixing in with rain. This gives rain a red appearance as it falls. The Met Office has also issued a yellow thunderstorm warning from this evening until Thursday morning in the southeast, including London.

The thunderstorms will cause a risk of flooding, which is likely to lead to travel disruption.

Richard Miles, from the Met Office, said: “There are some dust concentrations in the atmosphere above the UK at present which might well be washed out in the rain tonight, but it’s likely to be relatively small amounts on the whole.

“There’s a warning out for thunderstorms for the south-eastern third of England tonight, and a squally cold front will bring wind and sometimes heavy rain to Northern Ireland and northwest Scotland this evening.

“Away from these features it will be mostly fine and dry today and tomorrow, temperatures up to 23-24C in London and the South East, high teens or low 20s elsewhere.”

The Met Office said that the dust cloud is likely to come from the Sahara.

It said: “Each year on several occasions the UK will see rain falling with some amount of dust mixed into it.

“This usually comes from the Sahara before mixing in clouds and falling out.”

Explaining the “blood rain” phenomenon, the Met Office said: “In the case of blood rain, strong winds or storms can whip up dust and sand.

“As this becomes airborne it can get caught up in atmospheric circulation, where it can be carried for thousands of miles.

“Eventually the dust will either fall out of the sky due to gravity or will be caught up in rain clouds, where it mixes with the water droplets.

“When these fall as rain the raindrops could appear red.

“Proper blood rain, where the rain actually appears red, is relatively rare because you’d need red dust/particles in fairly high concentrations in the rain.”

Issuing a warning for thunderstorms earlier today, the Met Office said some parts of the UK will see “torrential downpours and frequent lightning”.

The extreme weather, it said, will develop throughout the evening.

The forecaster warned that “spray and sudden flooding could lead to difficult driving conditions and some road closures”.

It predicted “delays and some cancellations to train and bus services, as well as possible power cuts.”

The Met Office also warned that homes and businesses could be flooded, warning of “damage due to floodwater or lightning strikes.”

It said: “Developing showers and thunderstorms are likely to intensify across parts of the warning area through the evening, before easing away eastwards after midnight.

“Quite a lot of places will probably avoid the heaviest rain and thunder, but others could experience torrential downpours and frequent lightning, while large hail and strong wind gusts may also affect a few places.

“Central parts of southern England are perhaps most likely to see impacts.

“Rainfall amounts will be highly variable, as is usual in such situations, but the wettest spots perhaps seeing around 25 mm of rain inside an hour, and a possibility that somewhere could catch over 40 mm in 2 or 3 hours.”