Blizzards and dangerously low temperatures persisted in parts of Europe on Sunday, prompting Pope Francis to draw attention to the homeless suffering in freezing weather. In Serbia, aid workers scrambled to help hundreds of migrants sleeping rough in parks and makeshift shelters. The extreme winter weather that has gripped Europe in the past days has caused more than a dozen deaths, left villages cut off, caused power and water outages, frozen rivers and lakes, grounded flights and led to road accidents. Serbia’s authorities on Sunday banned river traffic on its stretch of the Danube — one of Europe’s main rivers...