Highway to Hail

On the evening of April 6th, 2010 we had a nice little storm system move through central Oklahoma.  Short term models earlier in the day were breaking out a supercell around the OKC area about sunset and though those models had done exceptionally well with events in the previous days they missed the storm type here.

On the right is a radar image from that evening where the boundary is visible.  About this time the storm was moving over Norman producing moderately high winds, heavy rain, and small hail.

Above is an image I took right before the precipitation hit Norman, as the hail began to fall I noticed that it was a prime example of what we had already been discussing in cloud physics.

Hail grows around a hail embryo.  Commonly this is graupel or large drops, but sometimes insects have become entrained in the updraft and become the center of a hailstone!  Hail can undergo 'dry' and 'wet' growth implying things about where it is in the cloud at the time.  Without going into too much detail on this we can say that dry growth produces much less dense hail (more air and cloudy looking) while wet growth produces clear layers of almost solid ice.  Switching methods of growth produces the 'onion' like texture on the inside of a hailstone that so many falsely attribute to multiple trips through the updraft.  The trajectory of most hailstones (we think) is remarkably flat!  It is rare for them to recycle through the storm and when they do its not multiple trips.

The shape of the hailstone also tells us about its environment.  There are many excellent papers out on the topic.  After looking at the image above of some hailstones collected from this storm I encourage you to read more on the topic and next time it hails be sure to pick some up and think about the environment that could have formed it.  Could this stone have recycled? Could it have been warmer than it's environment (think latent heating)? Did it melt significantly on the way down?

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