While activating W7M/GA-106 (Black Mountain) today I encountered some odd ice crystals (attached) which fell from the sky. The weather was cool (perhaps a bit above freezing) & we were in & out of a cloud as we ascended with episodic sleet coming down. A good proportion of the sleet was crystaline in nature. The sleet crystals were all quite angular, planar & striated in various sizes. The photo is one of the larger ones & had partially melted by the time I took the photo. Many were 1/4-inch (1-cm) or so in size. At first I thought they may be coming from the trees, but there was no snow or ice on the trees (at least within 1-mile or so) & they were clearly coming from the sky. They would sometimes “dump down” over a period of 1 or 2 seconds. The conditions were generally calm (non-windy), although there was a slight breeze.
I have often seen ice falling in the form of little prisms or platelets but that one in the photo is freakishly large, at least ten times bigger than the examples that I have seen! These platelets form in clouds under certain conditions and grow by accretion, you can see the growth marks, the striations parallel to the sides and ends of the prism suggesting that it was continually rising and falling in the icing zone until it got too heavy to be supported by convection. This is the sort of photo that should be in a textbook!
G8ADD:
That is interesting that you have seen platelets or prisms also. Were they similar in appearance?
I forwarded the photo to the general contact at the National Weather Service & whoever responded was of the opinion that it was most likely surface ice that was stripped from some other location (e.g. airplane or tree). That seems unlikely to me as they fell (off & on) over 30-minutes or so. Also, the orientation of the layering doesn’t seem correct for ice layering on a surface & it wasn’t remarkably windy. It was one of those days where some summits (like the one I was on) are hidden by a cold, damp cloud. I think there was more wind up higher, as once we got on top the clouds were moving by at a good pace.
One thing I do know - I would have never seen it if it weren’t for SOTA.
73,
Rob - AE7AP
