Practice indoors if you need to but what happens if the web bulb whatever that is says you can't play outside at 6pm when it's still 100 degrees outside during scrimmages?
My opinion may be unpopular but I say forget the wet bulb and just practice outside like we've been doing for years. Make sure the kids are hydrated and know to continue to hydrate throughout the entire day and through the weekend. Coaches if you see the kids in the hallway at school remind them all day long to get some water. Parents if your kids are gonna play sports get them outside some during the summer so their bodies can condition to the heat. Staying inside in the ac on those damn phones and games all summer long then going out into 100 degrees with pads and running around is gonna hurt anyone I dont' care how good a shape you're in.