From The New York Times:
A storm off the coast of Portugal and the heat dome over central Europe have worked together to produce conditions in the atmosphere that are forcing dust high into the air in Africa. Winds are carrying the dust as far away as France and Britain, where, as it falls to the ground, it may bring a reddish tint to the cities and towns still baking in one of Europe’s worst heat waves in years.
The air pattern is moving high above Europe in waves, and along its edge it is bringing a chance of rain and even thunderstorms, first to Spain and Portugal on Thursday. By Friday and Saturday, it may reach southern England, while France has a slightly higher chance of rain on Sunday. When the dust mixes with rain on its way back down to earth, the phenomenon is sometimes referred to, somewhat sensationally, as “blood rain.”