[Patrick1]

He can be sworn in as President anywhere at noon on January 20th. The Inauguration can be canceled if necessary. Ronald Reagan’s inaugural ceremony was canceled because of weather and done inside the capitol in 1985.

[thecodont]

"January 20 was a Sunday, and the President took the oath of office, administered by Chief Justice Warren Burger, in the Grand Foyer of the White House. Weather that hovered near zero that night and on Monday forced the planners to cancel many of the outdoor events for the second inauguration. For the first time a President took the oath of office in the Capitol Rotunda. The oath was again administered by Chief Justice Burger. Jessye Norman sang at the ceremony."

Reagan took his public oath of office on Monday, January 21, 1985. Washington's weather was bitterly cold and people were advised to stay indoors if at all possible.

Ronald Reagan's Second Inaugural Address, January 21, 1985