The phrase "thick as hail" is usually used to describe a situation where there are a lot of things or people closely packed together. There are several synonyms that can be used to describe such a situation. One of them is "crowded," which describes a place or situation that is full of people or things. "Jammed," "crammed," and "packed," are also good synonyms for "thick as hail" that convey a similar sense of proximity and congestion. Other appropriate synonyms include "dense," "congested," and "teeming." All of these words can be used to describe a crowded place, situation or event where there is little space for movement or breathing.