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Last night it dropped to around 25°F here in Wildwood, GA. I noticed what looked like patches of cotton on the ground that were not there the day before. At closer look they are patches of frost/ice. Some, like the image below, appear as if they were spun on a machine.

How do these patterns form?

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Below is another one (photo taken 11-20-2022).

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relayman357
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    It looks a bit like an ice spike, some of which take on a very non-spike-like form. – David Hammen Nov 18 '22 at 14:24
  • Thank you @DavidHammen, it did not look like ice at all. Then, when I picked one up it disintegrated as it is a very fragile ice formation. It is quite amazing to me. – relayman357 Nov 18 '22 at 19:14
  • So... meteorologist here... and I've never seen such a thing!!! Was sure it look fake! But justCal's answer seems legitimate, amazing! Have seen hoar frost and such, but that's amazing stuff. Of course living in FL most of my life... helps aid my lack of familiarity. I would think just the right wind is key too. Was it all over the yard, or only in certain areas? And did you notice if there was any light wind in the morning? And the direction? A nearby body of water? – JeopardyTempest Nov 20 '22 at 03:18
  • Just questions that may help be of extra interest in light of justCal's great answer and trond's great link! Proof we all still have much to learn in life! – JeopardyTempest Nov 20 '22 at 03:18
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    Hi @JeopardyTempest, they were in patches on edge of woods and along gravel road. Don't recall the wind conditions, but i would expect little or no wind as these things are delicate. No body of water nearby. – relayman357 Nov 20 '22 at 18:37

1 Answers1

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What you are looking at is called hair ice. The Wikipedia article seems a little unclear on the cause, but it seems associated with dead plant material, and the presence of certain fungi.

Hair ice forms on moist, rotting wood from broadleaf trees when temperatures are slightly under 0 °C (32 °F) and the air is humid.[1] The hairs appear to root at the mouth of wood rays (never on the bark), and their thickness is similar to the diameter of the wood ray channels.[1] A piece of wood that produces hair ice once may continue to produce it over several years.[1]

More information provided in comments by @trond hansen can be found in another article on Hair Ice at the UKs' Met Office

justCal
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    here is a bit more information and a video of hair ice forming https://www.metoffice.gov.uk/weather/learn-about/weather/types-of-weather/frost-and-ice/hair-ice – trond hansen Nov 19 '22 at 05:22