CHICAGO—U.S. carriers on Friday canceled thousands of flights through the weekend in anticipation of a winter storm forecast to bring high winds and heavy snow across the Northeast and Mid-Atlantic. The National Weather Service said in an advisory that the Nor’easter would result in dangerous blizzards and make travel “nearly impossible.” Flight-tracking service FlightAware reported about 4,900 U.S. flights were canceled between Friday and Sunday. Delta Air Lines said it would suspend operations at LaGuardia and John F. Kennedy airports in New York, Newark Liberty airport in New Jersey, and Logan airport in Boston from Saturday through Sunday morning. The Atlanta-based carrier canceled 1,290 flights from Friday to Sunday. Customers who would have traveled then were allowed to reschedule to different flights without extra cost. “Delta teams are focused on a safe and orderly restart of operations at these airports and others in the Northeast Sunday afternoon, depending on conditions,” …