Trump to be inaugurated inside: Last ceremony held indoors was Reagan's in 1985

On that frigid January 20th 40 years ago, the air temperature was 7 degrees, with a windchill of -40. 

Monday's forecast is a high of 23 degrees and a low of 10, but brutal winds are expected to whip across the city, making the temperature feel more like single-digits. 

"There is an Arctic blast sweeping the Country. I don't want to see people hurt, or injured, in any way. It is dangerous conditions for the tens of thousands of Law Enforcement, First Responders, Police K9s and even horses, and hundreds of thousands of supporters that will be outside for many hours on the 20th (In any event, if you decide to come, dress warmly!)."

Trump said D.C.'s Capital One Arena will be open Monday for live viewing of his inauguration "and to host the Presidential Parade." 

"I will join the crowd at Capital One, after my Swearing in," he wrote.