Il y a du brouillard.
Eel ee ah doo broo-YAAR
There is fog.
Simple
Il y a du brouillard ce matin, soyez prudents sur la route.
Eel ee ah doo broo-YAAR suh mah-TAN, swah-YEH proo-DAHN soor lah ROOT
There is fog this morning, be careful on the road.
Soyez prudents = be careful (plural/formal)
On est dans un brouillard à couper au couteau, on n'y voit rien !
On eh dahn uhn broo-YAAR ah koo-PAY oh koo-TOH, on nee vwah ryahn
We're in a fog you could cut with a knife, you can't see a thing!
brouillard à couper au couteau = fog so thick you could cut it with a knife, classic French
More French Weather Phrases