Seeing water in liquid form at sub-zero temperatures may seem surprising, but this phenomenon is well known to scientists. Called supercooling, it was first observed as early as 1724 by Gabriel Fahrenheit.
When water is extremely pure and free of crystallization nuclei, it can remain liquid down to about –40°C. This behavior is particularly observed in the fine droplets that make up high-altitude clouds. However, this state remains unstable: the slightest disturbance can cause rapid crystallization.
Translated with DeepL.com (free version)