WASHINGTON — The tanks are staged and ready to roll. Fencing and barriers are up. Protective metal plating has been laid out on Washington’s streets.

And more than 6,000 troops are poised to march near the National Mall to honor the Army’s 250th anniversary on Saturday, which happens to be President Donald Trump’s 79th birthday.

With preparations well in hand, one big unknown is the weather. Rain is in the forecast, so there is a chance the parade could be interrupted by thunderstorms.

White House spokeswoman Anna Kelly said Thursday that rain or shine the parade will go on. But it could be delayed if there is lightning.

“No matter what, a historic celebration of our military service members will take place!” Kelly said in a statement.

Daylong festivities celebrating the Army are planned on the National Mall — featuring NFL players, fitness competitions and displays — culminating in the parade, which is estimated to cost $25 million to $45 million. The Army expects as many as 200,000 people to attend.

A special reviewing area is being set up for the president, where he will be watching as each formation passes the White House.

Here’s what to expect at the parade Saturday:

The Troops

A total of 6,169 soldiers as well as 128 Army tanks, armored personnel carriers and artillery will parade before the president and viewers, while 62 aircraft will pass overhead.

The parade will tell the Army’s story, starting with the Battle of Lexington — the first battle of the Revolutionary War — and move all the way to present day.

Each conflict will have 150 troops in period costume, followed by a section of hundreds of troops in modern-day dress. For the past several weeks, Army planners have been working out how to get it timed to exactly 90 minutes, Army spokesman Steve Warren said.

Planners first tried marching troops five across and 12 deep — but the parade ran long. To get it down to the exact time, each section will have soldiers marching seven across and 10 deep, Warren said. That means, for example, the Civil War gets exactly three minutes and 39 seconds and World War II gets 6 minutes and 22 seconds.

The Tanks and Aircraft

Then there are the tanks. For fans, 8 minutes and 23 seconds into the procession, the first World War I Renault tank will make its appearance.

Compared with today’s tanks, the Renaults are tiny and almost look like a robotic weapon out of “The Terminator.” But they were groundbreaking for their time, lightweight and enabling movement in that conflict’s deadly trench warfare.

The first aircraft will fly over starting 13 minutes and 37 seconds into the parade, including two B-25 Mitchell bombers, four P-51 Mustang fighter aircraft and one C-47 Skytrain. The latter was made famous by the three stripes painted on the wings and body to mark it friendly over U.S. battleships on June 6, 1944, as thousands of Skytrain aircraft dropped more than 13,000 paratroopers into France on D-Day.

The procession will move along into the Gulf War, the war on terror and the modern day, showcasing the Army’s M1A2 Abrams tanks and other troop carriers, like the Joint Light Tactical Vehicle and Stryker combat vehicle.

There will even be six High Mobility Artillery Rocket Systems, or HIMARS — the mobile rocket launchers that have been highly valued by Ukraine as it has defended itself against Russia’s invasion.

A massive show of Army airpower will begin 48 minutes in, when a long air parade of UH-60 Black Hawk, AH-64 Apache and CH-47 Chinook helicopters fly overhead as the Army’s story swings toward its future warfare.

The Parade Finale

The final sections of marching troops represent the Army’s future. The band at the U.S. Military Academy at West Point will lead hundreds of future troops, including members of the Texas A&M Army Corps of Cadets, new enlistees just going through Army initial entry training, and cadets from the Virginia Military Institute and The Citadel in South Carolina.

The last section includes 250 new recruits or soldiers who are reenlisting. As they reach the president, they will turn toward him and raise their right hand, and Trump will swear them into service.

The parade will end with a celebratory jump by the Army’s Golden Knights parachute team, which will present Trump with an American flag.

After the parade, a 19-minute fireworks show and concert will round out the celebration.