January was 15% colder than the coldest month in the last four winters, which means that demand for heat was also very high. With energy costs at their highest levels in recent years, it was a double-whammy for utility bills. The demand for heat is measured in "degree days," a metric of how cold the temperature was on a given day or during a period of days. The higher the number of degree days, the more energy required to heat a space.
Monthly degree days in Philadelphia over the last four winters