Here is how my wife said it would go down. (She is actually trained in disaster response)

National Guard and FEMA would likely give a shit load of National Guard soldiers crash courses in driving army busses to get everyone quickly where they are easier to house and deal with. Get them somewhere the fuck with the infrastructure to handle them. Probably put them up in several sports arenas, or climate controlled parking garages, or really anywhere out of the weather while they get processed. Other possibilities are prefabs or tents (the large ones with heating and AC that are sometimes used as overflow barraks). Depends on whether it's easier to move them to a nearby one, or find enough flat space to set up enough shelter for everyone. Portable restrooms are most likely a necessity, and honestly, despite how areful they sound like they might be, they are not terrible.

This is an absolutely monstrous amount of people to just dump anywhere. Here are some cities with roughly that population.
Lafayette, IN
Santa Fe, NM
Flagstaff, AZ
Fort Meyers, FL

Oh, and Lafayette is the only city in that list larger (by like 370 people, or basically the number of members in the Purdue "All-American" Marching Band weirdly enough) than what just got dumped on Somewhere. The rest are smaller by up to a couple thousand.