Winter Wonders: How icicles get their unique shape

Weather Blog

ROCHESTER, NY (WROC) — Being in the heart of the winter season, it’s the time of year that brings with it plentiful build up of snow and ice on roofs and other buildings. When the sun comes out and warms things up a bit, you get one of winter’s staples: icicles! These pointy, carrot-shaped ice formations can form on roofs, branches, other ledges, and even bushes.

Icicle formation and growth might seem like a simple process, but there’s more going on in the process than you may think.


Icicles typically form on the edges of roofs during winter when the snow sitting on your roof melts. They will typically form on days when temperatures are still below freezing, but warmth from the sun or escaping from your home is able to heat the snow enough to melt it anyway. As the sun melts this snow and ice, the suspended water drips down your roof and slowly freezes. Icicles form from what’s known as a pendent drop, which is the drop of liquid water not yet frozen, which subsequently freezes from there. It’s this recurring cycle that helps icicles grow in length, given there’s a fairly steady stream of meltwater to fuel it.

Remember when I mentioned that icicles form from meltwater with a little help from the sun? It’s because of this why you may find more icicles on the sunnier side of your home than the shadier side. Check it out for yourself!

How do icicles get their unique shape?

Image by M. Maggs from Pixabay

As liquid water freezes it releases heat energy under a phenomenon known as latent heat. It’s the process where temperature exchanges result in the release or absorption of energy due to changes in phases (i.e. solid, liquid, gas). Icicles are pointy at their ends because of this process. Why? As water continues to melt and refreeze along the tip of the icicle, this latent heating focused at the very tip slows down the growth rate towards the bottom of the icicle. When air moving up the icicle allows more water to slide upwards and freeze towards the top, it also creates a thicker base than at the tip. This process overall controls how fast or slow icicles form, and therefore how long they appear next to others.


The ice that forms on your roof and gutters isn’t always just pretty to look at, but can also form as chunks of ice that can potentially cause damage to your home.

MORE⼁Icicles and ice dams wreak havoc on homes as snow melts

Icicles if they fall, can really hurt someone, or cause damage to cars and property. Be sure to always look up when passing underneath any roof or suspended object holding a large amount of icicles, and be aware of your surroundings.

Something to consider:

It’s not uncommon to be tempted to pick off the best icicle off of your house, and maybe even eat them. While it may be fun to do so, it may not be the most clean. Remember that the meltwater contained within those icicles came right from the top of your roof and gutter. Both of these places can be home to dirt, chemicals, and even…ahem…leftovers from birds, squirrels, etc so be careful when going to pick off that perfect icicle.

~Meteorologist Christine Gregory

Copyright 2021 Nexstar Inc. All rights reserved. This material may not be published, broadcast, rewritten, or redistributed.

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