December 5, 2013; 9:10 PM ET
After basking in balmy air much of this week, a return to colder weather will be accompanied by multiple rounds of wintry mix into early next week around Philadelphia. more >
Snow between Sunday afternoon and Sunday evening will accumulate 1-2 inches before changing to rain
The sheer number of people, their interactions with animals and ecosystems, and the increase in international trade and travel are all factors that will likely change the way humanity deals with preventing and treating epidemics, experts say.