DALLAS—Higher temperatures spread across the southern United States on Saturday, bringing relief to a winter-weary region that faces a challenging clean-up and expensive repairs from days of extreme cold and widespread power outages. In hard-hit Texas, where millions were warned to boil tap water before drinking it, the warm-up was expected to last for several days. The thaw produced burst pipes throughout the region, adding to the list of woes from severe conditions that were blamed for more than 70 deaths. By Saturday afternoon, the sun had come out in Dallas and temperatures were nearing the 50s. People emerged to walk and jog in residential neighborhoods after days indoors. Many roads had dried out, and patches of snow were melting. Snowmen slumped. Linda Nguyen woke up in a Dallas hotel room Saturday morning with an assurance she hadn’t had in nearly a week: She and her cat had somewhere to …