Quote:
Originally Posted by sounding
In the early morning of Dec 9, 2024 it snowed over the Soulliere Villas (near the First Responders Recreation Center). The snow never touched the ground because it evaporated in the dry air below the clouds. This type of high level precipitation is called virga -- and in this case it is called snow virga. We know it was snow (and not rain) because the temperatures at that altitude were about -50 F.
|
True for the most part, but not always.
"Supercooling,[1] also known as undercooling,[2][3] is the process of lowering the temperature of a liquid below its freezing point without it becoming a solid. As per the established international definition, supercooling means ‘cooling a substance below the normal freezing point without solidification’ [4][5] While it can be achieved by different physical means, the postponed solidification is most often due to the absence of seed crystals or nuclei around which a crystal structure can form. The supercooling of water can be achieved without any special techniques other than chemical demineralization, down to −48.3 °C (−54.9 °F). Supercooled water can occur naturally, for example in the atmosphere, animals or plants."
Those of us from the far north know about this because we sometimes see it in action, and it is not always a pleasant circumstance. Driving to Duluth one January morning some years back on I-35 we crested Thompson Hill, which is at about 600' higher in elevation than most of the city. Beautiful clear morning, maybe -25 or so on the thermometer. There was a slight haze ahead of us but that is not uncommon when elevations change during winter driving, though I did slow down just to be safe. Good thing I did. The dull black color of I-35 all of a sudden changed to a shiny black color and ice appeared on the windshield. I-35 had changed from a highway to a skating rink in the space of maybe two hundred yards. Several cars spun out behind us. Didn't last long--maybe half a mile or so, but that 1/2 mile was a real sphincter-clenching experience.
Mostly that supercooled water in the atmosphere will adhere as ice to tree limbs, wires, etc., changing the scenery to sort of a fairyland look especially in the bright morning sun. The trees will sparkle like diamonds. But when it adheres to highways it can be frightening, even deadly, because of how fast it can happen.