Christmas Eve and Christmas Day 2015 experienced some of the highest temperatures on record. Temperatures reaching the 60s and 70s in the Northeastern United States and some records being broken by more than 10 degrees. Some meteorologists attributed the warm weather to El Nino, while others claimed the warm weather was caused by a high pressure ridge in the Eastern United States.
Some effects of this warm weather include lack of snowing the northeast, leading to a difficult beginning of the season for ski resorts.
Sources:
http://www.weather.com/forecast/national/news/warm-united-states-december-2015
http://i.dailymail.co.uk/i/pix/2015/12/21/20/2F8E1ECF00000578-3369427-image-a-15_1450728841390.jpg
http://www.cnn.com/2015/12/25/us/warm-christmas/