Loom large
Definition 1 of 1
Pro Tip 1/3Immediacy Impact
Used when something is about to happen or become a problem soon, implying urgency or prominence. 
The looming deadline for the project loomed large in her mind.
Pro Tip 2/3Negative Connotation
Often has a negative feel, referring to problems or challenges that are difficult to ignore. 
The possibility of rain loomed large over the outdoor wedding.
Pro Tip 3/3Figurative Use
Can be metaphorical, not just literal size or presence. It’s about the level of influence or effect. 
The legend of the star player loomed large at the school.