Since the YMCA is an indoor pool, practice is rarely cancelled due to weather; however the pool is not grounded so if lightning is in the area the swimmers will not be allowed in the water or on the pool deck. If this is the case, the coaches will make a determination to either have the swimmers do dryland practice inside the YMCA or the cancelled practice altogether.
It's important to bring sneakers and shorts on days that dryland practice is possible - it's not safe to do dryland barefoot or in sandals (examples of practice: kids might run on the indoor track, do resistance training, or do ab workouts in the gym) so appropriate clothes are necessary. Also - dryland can be tough on team suits so workout clothes are recommended.
The coaches may also shorten dry land practice times compared to normal practice so watch your emails during storms for notices of practice ending early.
Use your own judgement to decide if it's safe or not to travel to and from practice from your area.