Donald Trump's plans to stage "the show of a lifetime" for America's Independence Day celebrations is facing the threat of thunderstorms.
Heavy rain and storms are set to batter Washington on Thursday which will make conditions for a planned military flypast difficult.
The storms are expected to begin mid-afternoon and go on until midnight local time.
NBC weather forecaster Doug Kammerer said: "There's going to be a lot of rain during the duration of the celebrations.
"Rain is set to hit Washington at around 9pm – just when the firework display is about to start. But it's going to be wet and stormy most of the day."
However, Molly Block, spokeswoman for the Department of Interior, reportedly said: "We fully expect (Thursday's) events celebrating Independence Day on the national mall to take place rain or shine."
Thousands of revellers – and protesters – are expected to flock to Washington's national mall where tanks are in place for the display of US military muscle.
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It is almost seven decades since a president spoke on the mall on Independence Day.
The US was at war in Korea when US President Harry Truman addressed a large gathering on the Washington monument grounds in 1951, marking the 175th anniversary of the signing of the declaration of independence.
Mr Trump has described this year's event as a "salute to America" to honour the armed forces.
The president will speak at the Lincoln memorial in front of a ticket-only, VIP crowd of Republican donors, administration and campaign officials, family members as well as the public.
The Pentagon is arranging for an Air Force B-2 stealth bomber and other warplanes to conduct flyovers.
There will be Navy F-35 and F-18 fighter jets, the Navy blue angels aerobatics team, army and coast guard helicopters and Marine V-22 Ospreys.
Mr Trump defended spending on the event, tweeting that the cost "will be very little compared to what it is worth".
"We own the planes, we have the pilots, the airport is right next door (Andrews), all we need is the fuel," he said, referring to Maryland's Joint Base Andrews, which is home to some of the planes.