Why Are There Still Southern Snowbanks? Latent Heat Takes Time

Old snow piles take forever to melt. 

Every spring, we in Vermont see dirty, sad monuments to the past winter. 

They're in the form of those dirty, ugly slowly fading piles of snow at the edges of supermarket parking lots and back behind strip malls. The piles are a remaining bit of late winter grossness while trees bud and flowers bounce happily in the spring breezes nearby. 

This spring, people in the the southern United States had the rare opportunity to experience these fading remembrances of winter and they were freaking out. 

Usually when it snows in the south, it's usually a wet, heavy slop that's so close to water anyway that it melts quickly. Or it's a quick shot of fluffy, usually a couple inches at most.

This winter, a huge swath of the South, Midwest and Mid-Atlantic States got basically snowy cement in January. It was a dense mess of snow, lots of sleet, all frozen together by a round of freezing rain. 

In February, southerners freaked out this mess wasn't melting, despite temperatures occasionally poking well above freezing. The conspiracy theories swirled. It wasn't melting, so it wasn't "real" snow. The government, the corporations, the oligarchs were doing.....something.

But there's reasons why that snow and ice didn't melt fast. We'll get to that in a minute. 

Then, the dirty icy "monuments" in the parking lots in the South remained well into March. That's normal for us in Vermont, but it's completely bizarre for people in Tennessee, or Virginia or even Maryland and New Jersey.   

The conspiracy theories started again. Snow always melts way before now! Something is wrong! say the worried conspiracists.  Even if people didn't believe the conspiracy theories, they still remarked about black piles of debris in Philadelphia in late March that were in fact leftover snow piles. 

Montclair, New Jersey residents are annoyed by lingering snow dumps in parks.  The snow was removed from streets in the winter, and left in the parks. As of earlier this week, much of the snow was still there, covered in grime and flecked liberally with trash. Big piles of "snowcrete" remained at the airport in Baltimore as April arrived. 

Now all these residents get to enjoy what we Vermonters do: On top of our mud season, the rotting piles of dirty snow  in parking lots and the grimy puddles surrounding them are as much a scene of spring as crocuses and budding trees.

Big old snow piles need a lot of what is known as latent heat of fusion to completely melt.  Latent heat of fusion is just the energy needed to turn ice from a solid into a water a liquid. That's not the same as temperature. It's not a matter of just heating up the ice. Energy has to go into the process of converting ice to water. 

According to the Boston Globe via Mental Floss: 

The piles are dense and heavy, especially since they formed in large part from sleet in addition to some snow. The piles were plopped there, become even more dense and heavy. The snow closer to the surface  starts acting as an insulator for the snow buried further down. The compact snow requires more energy to dissipate.

If you really want to get rid of an old ugly snow pile, you can spread it out with a shovel or backhoe. If more surface is exposed to the air, it will melt faster. If you don't have the energy to do that, pray for rain.

A well soaked snow pile melts faster than one that sits out there day after dry, sunny day .

And it could be worse. In the winter of 2015, Boston had epic amounts of snow, we're talking several feet in a few weeks. The city piled snow in back lots in a desperate attempt to get it off the streets. Not all of that 2015 snow melted until July.