Ditto here. I recently participated in a table top exercise that simulated a spontaneous evacuation from Vancouver BC south to Seattle and Portland. We had a land border to contend with (throughput - Customs will process only so many travellers per hour), 4-6 hours between the border and Seattle, a winter storm that hampered travel, and a reduced likelihood that every one from 1MM+ might self-evacuate. We ended up feeding and sheltering just over 30,000, with many more covered by cities all along I-5 as far south as Portland. All in all it was an interesting excercise, and the major takeaway for me was we were in need of more volunteers to cover all the shelters we eventually opened.

Dagny, if I can recommend - if you want to help organizations during such an event, volunteer with them now: taking in spontaeous volunteers during a disaster can happen, but most relief organizations will thank you for signing up ahead of time. The Red Cross has something called the Reserve Corps, for volunteers who don't want to volunteer for routine fires and flooding, but may turn out for larger events. You do one day of training, and a criminal background check, and are issued a RC ID. Check with your local chapter to see if they currently offer Reserve Corps in your area.