An evacuation was ordered Saturday evening at the National Mall as storms gathered around Washington just hours before U.S. President Donald Trump was scheduled to deliver a speech commemorating America's 250th anniversary of independence.

Trump vowed to deliver a "really long" Fourth of July address despite a 107-degree forecast at the America 250 celebration.

Washington's July 4 celebration attendees this year will have to contend with stepped-up security, possible thunderstorms and temperatures that could top 100F.