While the skies will go black for only a few minutes Monday, local governments around the country have spent years preparing for the astronomical spectacle on a disaster-level scale.
Medical centers have lined up extra ambulances and hospital beds. Emergency call centers have beefed up 911 staffing. And first responders are prepared to lean on ham radio operators or pay phones (the ones that still exist) in case their calls can't power through the onslaught of celestial selfies jamming cellphone towers.
Emergency planners know the sky is going dark, not falling.
But unlike preparing for an Inauguration Day crowd or natural disaster, the eclipse isn't confined to a particular location. Rather, millions of eclipse enthusiasts traveling this weekend are expected to strain roads, communications and public safety resources simultaneously across multiple states as they flood the 70-mile-wide strip that will experience total darkness coast-to-coast.
Drivers looking up at the sky could trigger traffic accidents. Visitors camping in unusual places could spark wildfires. And callers worried about the weather, road conditions — and yes, where the sun went — could overwhelm 911 call centers.
"All of that occurring in 14 states in a 70-mile swath for 3,000 miles," said Brad Kieserman, vice president of disaster operations and logistics for the Red Cross. "That makes this a little different from your garden-variety disaster."
More than 12 million live in the path of totality, the limited band across the United States that will experience the shadow of the moon completely blocking out the sun. But another 1.8 million to 7.4 million are expected to travel to the path, according to estimates from GreatAmericanEclipse.com.
Businesses have been told to stock up on gasoline, food and water to accommodate visitors eager to experience what experts say will be the most-watched astronomical event in a century.
"Bottom line, we do not have the infrastructure," said Mark Carman, emergency management coordinator for Jefferson County in Oregon, which estimates at least 1 million eclipse fans will visit the state. "But if you throw us a problem, we're going to give you a solution."
The county has rented an extra 400 portable toilets and 40 waste bins. They've brought in more ambulances from neighboring jurisdictions. And — because it is wildfire season in Oregon — authorities have strategically placed fire engines throughout the state to cut down on emergency crews having to travel through eclipse traffic.
Carman said he's asked ham radio operators to stay close to their equipment in case cell towers jam and emergency medical responders need a communications hand.
At first, it seemed as if the county about 2 ½ hours southeast of Portland would welcome about 20,000 enthusiasts, said Carman, who started planning for the eclipse more than 2 ½ years ago. But the number has swollen to an estimated 100,000 — 15 times the population of the county's biggest city of Madras.
"I've been in emergency services my whole life and I can't even wrap my head around the whole thing," Carman said.
The District and its suburbs sit outside the path of totality and will experience a partial eclipse. Local first responders aren't preparing to the same level as communities that will blackout 100 percent. But there are still some safety worries.
"Distracted driving is a high concern for all of us on that day," said Mark Brady, a spokesman for Prince George's County Fire and EMS. "People may be trying to look upward instead of straight in front of them and that certainly is a safety issue."
South Carolina is the closest point for Washington-area residents who want to travel to experience the best view of the eclipse. The state expects anywhere between half a million and 2 million people for the event, said Kim Stenson, head of the South Carolina Emergency Management Division.
While big cities such as Charleston are used to hosting big crowds for festivals and sporting events, the state has never managed multiple events across the state at the same time.
"The influx of visitors is a new twist," said Stenson, whose emergency managers are more accustomed to readying for natural disasters. "When you have a hurricane, you're probably going to have people leaving here, not coming here."
Police officers and firefighters will be strategically stationed throughout the state, though there could be some public safety delays, she said.
Sara Crosswhite, operations manager of the 911 center in Deschutes County, Ore., said the county's population is expected to double with the 200,000 estimated visitors.
Crosswhite will ramp up 911 staffing to handle the expected influx of calls. She and others reminded people not to call 911 unless it is for a true emergency.
"This is for life and death stuff that we need to get our responders moving to quickly," Crosswhite said.
Salem Health, one of the busiest hospitals in Oregon, has canceled elective surgeries and prepared three large air-conditioned tents to sit outside of the facility to handle incoming patients. The emergency department has boosted staffing by 15 to 20 percent.
"Originally when I first heard about the eclipse, I thought, 'What's the big deal? It's going to be dark for a couple hours,' " said Wayne McFarlin, the emergency preparedness administrator for Salem Health.
Then the numbers hit. With an estimated 25 percent spike in population statewide, one of the busiest emergency rooms on the West Coast had to prepare for a patient surge at least as large.
The hospital expects to treat increased patients because of infections from people crowding campsites, drug and alcohol overdoses and injuries from traffic accidents.
"We have not historically seen an event like this," said Ernie Rhodes, the state emergency manager for Missouri. "It may hinder normal everyday response and fire and EMS."
Authorities are reminding travelers to have food and water in their cars in case they get stuck in gridlock, to carry extra cash in case ATMs run out of money and — above all — to be patient and prepared.
But Rhodes said planning for the eclipse isn't keeping them up at night. "If everyone behaves," he said, "it is going to be a good day, it is going to be a really cool event."