about to get way more intense. a massive wall of rain is about to hit the northern part of the state, and communities are bracing for mudslides and dangerous flash flooding. the storm system heading to the west coast is so ferocious, it's known as a bomb cyclone. and it's helping to drive a river of moisture towards northern california. massive rainfall and strong winds are on the way. in areas scorched bare by wildfires, flash flooding, and mudslides could pose grave danger. >> the water flows off instead of soaking in,s and it can start picking up pebbles and bolders and the trees. and it can be severely damaging. >> reporter: marty ralph is an expert on weather and water extremes at u.c. san diego. on a scale of one to five, he says this system is a five. in area like nevada county hit hard by the river fire, emergency officials are telling residents to be ready to evacuate once again. >> if they say evacuations, i'll