From the US National Weather Service
We wanted to take this opportunity to show the challenging temperature forecast on Christmas Day. The 2 graphics below show the ensemble forecasted max temperature and the spread in max temperatures the ensemble shows. When there are varying solutions in the max temperature within the ensemble, then the spread will increase.
For example, on Thursday we have a situation where the ridge in the west could build and nudge east allowing higher temps, but we also have members within the ensemble that show the trough off the east coast deepening allowing lower temps. Thus, a location such as Pittsburgh could have a high temperature between 51 and 60. The highest difference is in the northern counties, where a warm front, depending where it sets up, will make a huge difference in temperature.
The bottom line up front is to be prepared for a fluctuating temperature forecast for Christmas Day.
