(USA TODAY) -- Along with the weather forecast and airport crowd, the national holiday checklist now routinely adds another staple: terrorist threat alert.
This July Fourth weekend is no exception, with federal intelligence agencies reminding local law enforcement "to remain vigilant during upcoming national holidays and military events due to the heightened threat of attacks."
Such warnings around major holidays have become routine since 9/11, although federal agencies acknowledge there are no specific or credible threats to the United States this weekend.
Still, the July 4th holiday — with its patriotic symbolism — seems particularly vulnerable to possible terrorist attacks, most notably lone wolf assaults, wherever crowds gather for ballgames, concerts and firework displays.
Concern this year has centered around the rise of the Islamic State and the danger of an attack either directly, or from an individual inspired by the terrorist group.
Homeland Security Secretary Jeh Johnson said recent terrorist attacks in three countries — France, Kuwait and Tunisia — are a reminder of the threat potential. He pledged vigilance by U.S. authorities.
In Washington, where huge crowds are expected for annual the fireworks display near the Lincoln Memorial, authorities have erected 18,000 feet of fencing and will require visitors to go through one of nine checkpoints.
New this year: no drones are allowed. The U.S. Park Police said no launching or landing of drones is permitted in National Park Service areas. Alcohol, weapons and personal fireworks are also not allowed.
In New York, Gov Andrew Cuomo placed his state's emergency operations center on higher alert Friday because of the federal warnings around the holiday. He urged people to "not only remember the freedoms that we hold dear, but also remain cautious of their surroundings and learn to recognize and report suspicious activity."
In New York City, 7,000 officers will be assigned to specific potential targets as New Yorkers gather to view the Macy's fireworks show on the East River. Police will also use radiation detectors.