Unusual Hail Encounters

[Steve Miller TX]

Back on April 12, 2009, I experienced one of the strangest weather phenomenon....snowball hail. Has anybody else ever experienced this? I'd love to understand the meteorological processes involved. I have theories, but it's just that and based on my amateur meteorological knowledge. Any other strange or unusual hail experiences out there?

 

[John Farley]

What was the temperature? I would suspect one of two possibilities. First, large graupel or some kind of hail/graupel hybrid. Graupel forms through "dry growth" or "dry accretion." This occurs when a snowflake becomes rimed, that is, rime accumulates on a snowflake. For this to happen, the snowflake must pass through supercooled water droplets, i.e. droplets that have a temperature below freezing but are still liquid. In this condition, rime forms on the snowflake, just like freezing fog. Rime has a softer consistency than regular ice, kind of like styrofoam. If the updraft is strong enough, the chunks produced by dry growth can get pretty big - reaching a point where they are usually considered a form of hail, but often softer than what we would normally call hail. Ordinary, hard hail, by contrast, occurs through "wet growth" or "wet accretion." This occurs when the snow passes through water droplets that are not supercooled (i.e. above freezing) but are then lifted to an updraft to where they freeze. This results in a hard hailstone. Sometimes both processes happen, and you get the kind of hybrid stuff like I saw near Pagosa Springs a couple years ago, up to quarter size. This may not be a perfect explanation meteorologically, but it is the general idea.

The other idea that occurs to me from looking at your video is that they could be big snowflakes that went through some melt-freeze processes as they were lifted by updrafts and fell. Either this explanation or the other one would be more likely if the storm was occurring in a cold environment, with surface temperatures, say in the 30s or 40s.

 

[Steve Miller TX]

Surface temperatures were in the 70's and the storm had a SVR on it. I can't recall the vertical thermal profile though of that day. I need to go back and do some research on that. In addition to your explanation, I likened it to what you see with a convective snow band where huge snowflakes fall....actually clumps of several snowflakes. In this case, the convective process of course was more intense. The thing that keeps my puzzled though is the packed density of these "hail" balls. As you can see towards the end of the video when I pick them up off the ground, it was quite compact exactly as if somebody packed a snowball.

 

[Steve Miller TX]

Storm reports from that day: http://www.spc.noaa.gov/climo/reports/090412_rpts.html

Analysis including ~-22C at 500mb and ~-2C at 700mb: http://www.spc.noaa.gov/exper/archive/event.php?date=20090412

 

[John Farley]

In addition to your explanation, I likened it to what you see with a convective snow band where huge snowflakes fall....actually clumps of several snowflakes. In this case, the convective process of course was more intense. The thing that keeps my puzzled though is the packed density of these "hail" balls. As you can see towards the end of the video when I pick them up off the ground, it was quite compact exactly as if somebody packed a snowball.

Yes, those are what I was thinking of in my second suggestion. I would think that if those went through some melt-freeze cycles falling and getting lifted, they might get that snowball feeling. 70s at the surface and below freezing at 700mb suggests a pretty steep lapse rate - and you didn't have to go too high to get below freezing, despite the warm surface temperature. Generally when I have seen stuff like this it has been a lot colder at the surface, 30s or 40s in the precip area and maybe 50s outside it is sunny areas. Interesting case!

 

[Paul Knightley]

Could it be a larger form of graupel (previously known as soft hail)? http://en.wikipedia.org/wiki/Graupel

I suspect not, as it's within a deep convective cloud, but we get such stuff falling at times in the UK in winter out of convective clouds (albeit they are rather shallow).

 

[Jeff Duda]

I bet it's a combination of dry growth and accretion of graupel particles once they fell into a layer with liquid water present, allowing them to aggregate as they fell.

 

[calvinkaskey]

I had New York sized stuff.

 

[Greg McLaughlin]

Terrence Cook and I chased a supercell in central Oklahoma on March 29, 2013 where the hail core was maybe 100-200 yards away with hail covering the road while no hail was falling over us. This persisted for several minutes. It was pretty cool being able to stand next to a hail core and hang out. Also of note: this was our first chase of 2013 near El Reno. We would end our season on May 31 again at El Reno.

 

[Stephen Levine]

Back on April 12, 2009, I experienced one of the strangest weather phenomenon....snowball hail. Has anybody else ever experienced this? I'd love to understand the meteorological processes involved. I have theories, but it's just that and based on my amateur meteorological knowledge. Any other strange or unusual hail experiences out there?

I wish all hail could be like that! I would core punch like a free bird!