In the event of a true disaster that requires people to leave large cities on foot, a lot of people who wait until the disaster happens will most likely die either in the city or on the way out from violence or lack of water. People attempting to flee in freezing temps or serious heat will die sooner.

Do yourselves a favor. Get out now or plan to stay where you are until murdering thugs have died out and water and food are restored and pray it isn't freezing or scorching outside.