A family walks home from the grocery store in Lancaster, Pennsylvania, in 2010.Carolyn Kaster / AP

Lines of frantic shoppers have mobbed grocery stores in Washington, D.C., after the National Weather Service gently advised residents on Wednesday that an intense weekend storm will pose “a threat to life and property” and impact “you, your family, and your community.”

Which led me to wonder: After people hear a message so ominous, and after reminders of their employers’ inclement-weather policies hit inboxes, what do they buy to prepare for spending a good deal of time indoors? I called up the managers of some grocery stores in D.C. to find out, and they all had more or less the same answer: bread, milk, and eggs. This holy trinity of winter-storm preparedness is not some quirk of the nation’s capital—bread, milk, and eggs are popular panic-buys everywhere from Knoxville to New England.

Now, I get bread. It doesn’t need to be cooked or refrigerated, and it goes with just about anything. The CDC even recommends it as something to have on hand for storms. But milk and eggs? Why, when the concern is that the power might go out, do people hoard things that need refrigeration, or even cooking?

There are some theories out there about the roots of pre-storm hoarding, most of them reasonable enough. “We spend a lot of time and energy trying to feel in control, and buying things you might throw out still gives the person a sense of control in an uncontrollable situation,” a psychotherapist told How Stuff Works. And one clinical psychologist suggested that buying things that might spoil is an assertion of optimism: It’s “like saying, ‘The storm will be over soon and I won’t be stuck in this situation for long.’”

But those explanations cover stockpiling in general, not why people particularly like hoarding bread, milk, and eggs. Peter Moore, the author of The Weather Experiment: The Pioneers Who Sought to See the Future, told me that while he didn’t have any definitive answers, he did have an idea. “We're encouraged, both by the modern media and by our primitive survival impulses, to project these extreme narratives—‘We're going to be buried in the house for a week,’ etc.—and people generally end up feeling very vulnerable,” he wrote to me in an email. “It must have something to do with the perceived comfort and safety of [those] particular products.”

That may sound like a stretch—the imposition of a highly abstract explanation on a banal shopping decision—but it has some merit. Weather, Moore reminded me, “is still the most capricious and mysterious force in nature.”

That might hint at why these particular foods are popular right before extreme weather, but it doesn’t get at why they are so popular. In the days preceding a big storm, stores are mobbed—shelves of bread are left skeletally bare, baskets are left abandoned near checkouts by the impatient, and the tiled floor near dairy fridges can be speckled with fallen egg cartons. Dan Ariely, a behavioral economist at Duke University, thinks that this might be the product of groupthink. “If we go somewhere and we see other people buying those particular things,” he says, “all of a sudden [we’re] even more interested in those [things].” One consumer psychologist quoted by Time has taken this a step further, speculating that “we are prewired to fight for food when we sense that resources are scarce.”

My experience, for what it’s worth, is that I go into a different mindset when I imagine myself cooped up indoors. Storms can of course wreak awful damage, but for most people they are a harmless annoyance and perhaps even an excuse to stay inside—a culture-wide justification for renouncing FOMO for a day. To stock up on cozy foods like milk and eggs is to clearly demarcate the storm as a time to put on sweatpants and not go anywhere. Buying a bunch of canned foods—a more practical choice—is decidedly less cozy, and may even carry unwanted survivalist overtones.

There is also the chance that it’s simpler than any of these theories. “I'm thinking you’re over-thinking this,” says Perry Samson, a professor at the University of Michigan and a co-founder of Weather Underground. “People simply feel that they have to do something and staples are easy. If the storm is bad they’re covered, if not they’ll use it sooner or later.”

Regardless, in all this theorizing, I’ve left out a notable pre-storm purchase. Ben Orlove, an anthropologist at Columbia University who specializes in climate science, points out: “The other thing that people stock up on for hurricanes, in Florida at least, is alcohol,” he says. “There are these hurricane parties, and people buy beer. I don’t know if that’s the case during winter storms.” It probably is.

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