Anyone who has ever spent time in the southeast knows how ubiquitous Waffle House restaurants are. The greasy spoon chain with 2,100 locations and all the comfort food you could ever want is everywhere — and that’s an especially good thing as Hurricane Florence blasts its wrath on the East Coast, with the Carolinas in its crosshairs.

Still, many don’t realize that Waffle House diners also double as barometers for how well areas are recovering after natural disasters strike.

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Incredible but true: The Federal Emergency Management Agency (FEMA) monitors what it terms a “Waffle House Index,” a color-coded indicator of what restaurants are open, closed, or offering a limited menu, in order to gauge how well an area will recover from a hurricane, tornado or other hazard, according to reporting from USA Today.

With restaurants located mainly across the south and along the Gulf Coast, open 24 hours a day, 7 days a week, and 365 days a year — it’s a big deal when Waffle House closes its doors.

“The Waffle House test just doesn’t tell us how quickly a business might rebound — it also tells how the larger community is faring,” reads a FEMA blog post from 2011, according to USA Today. “The sooner restaurants, grocery and corner stores, or banks can reopen, the sooner local economies will start generating revenue again — signaling a strong recovery for that community.”

Hurricane Florence is currently battering the North Carolina coastline and it’s not going away anytime soon, reports WTVD-TV, the ABC affiliate in Raleigh-Durham, North Carolina.

Related: Fierce Florence: 300,000-Plus People Without Power as of Early Friday Morning

Meanwhile, “Waffle House has a very simple operational philosophy: Get open,” then-FEMA Administrator Craig Fugate told The New York Times in 2012, according to reporting from WTVD.  “They never close. They run 24 hours a day.”

“They have a corporate philosophy that if there is a hurricane or a storm, they try and get their stores open,” Fugate continued. “It don’t matter if they don’t have power, it don’t matter if you don’t have gas. They have procedures that if they can get a generator in there, they’ll get going. They’ll make coffee with bottled water.”

As for the FEMA index, it has three color-coded levels. “Green means everything is fine, at least in the Waffle House; yellow is when the restaurant serves a limited menu, meaning the area lost power or they’re running low on supplies; and red is if it’s closed, showing the area has been hit hard,” according to reporting from the New York Post.

The chain posted a photo Wednesday of corporate employees monitoring the storm’s path as they discussed whether any locations would close.

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“The Waffle House Storm Center is activated and monitoring Florence. Plan ahead and be safe,” they tweeted.

See more on the Waffle House Index in the video below.

Elizabeth Economou is a former CNBC staff writer and adjunct professor. Follow her on Twitter.