It's moot at this hour but the reason for leaving the halters w/ID on your horse, in addition to painting on contact info, is so that IF your horse gets loose and it still has it's halter on, someone may be able to catch it. In emergecny's like this we must consider that non-horse people may be able to help with some tools in place. The odds of a break-away halter being in a problem in this storm are far outweighed by the potential benefit, IMO and experience. Even the spray paint and grease paint can be washed off in heavy rain so a halter w/ ID gives owners a little extra help.
I live in Kansas and when we are under a tornado warning, not just a watch, and if the storm system is looking like things could get messy here I leave halters on all of my horses- the big and small ones. In my rural area everyone knows everyone elses horses but I want them to be able to catch and tie them up somewhere secure until I can reconnect with them.
Stay safe those of you who are in or near harms way.