Some people keep an eye on the S&P 500 index. Others, on the Waffle House Index.

It all apparently began with former head of the Florida Department of Emergency Management, William Craig Fugate. Fugate would use the Waffle House diner chain as a proxy for how businesses and communities in the surrounding area were recovering after a disaster.

The Index (WHI) is pretty simple, as a FEMA blog post explains:

• If a Waffle House is open and serving its full menu: green. That means the diner probably has power or is running on a generator.
• If a Waffle House is open but serving a limited menu: yellow. The diner probably doesn’t have electricity or running water but can still cook on a gas stove.
• If a Waffle House is closed: red. The disaster is bad enough that not even Waffle House is serving eggs and grits.

The WHI is a good proxy because the Waffle House – open 24/7, 365 days a year – has excellent risk management procedures in place and often stays open during natural disasters. If even the Waffle House is closed, then you know the situation is bad and the broader community is likely severely impacted.

The I.I.I.’s own Lynne McChristian was once able to grab dinner thanks to a code yellow WHI. “During the 2004 hurricanes in Florida, the disaster response team I was leading lined up outside Waffle House for dinner, as it was the only place open,” McChristian said. She fed six people for $30. Not bad.

The WHI is so good a proxy, in fact, that even FEMA keeps an eye on the index during a natural disaster.

Back in 2016, the WHI went red before Hurricane Matthew hit Florida. As FiveThirtyEight reported, it sparked a, well, colorful reaction:

Waffle House announced Oct. 6 that it was pre-emptively closing some restaurants on a 90-mile stretch of Interstate 95 between Fort Pierce and Titusville in Florida. (In the next few days, as the storm churned up the coast and flooded North Carolina, it would close 98 all told.) And as soon as the announcement went out, media tracking the storm, and customers on social media, invoked the closings as a sign of the apocalypse.

The Miami Herald: “When Waffle House surrenders to a hurricane, you know it’s bad.” The Washington Post: “Hurricane Matthew is so scary even the always-open eatery is evacuating.” A faithful customer on Twitter: “GOD IN HEAVEN THIS IS THE END!”

For those in the path of natural disasters (including tornadoes): stay safe and keep close watch on the WHI to see if you can still get an All-Star Special after the storm is over.