AUSTIN, Texas - Supercell thunderstorms on radar are some of the most complex weather systems on the planet. They have all sorts of unique features that can be identified while watching the storms on radar.
One of the oddest radar features a supercell can have is a random-looking triangular spike out the side of the storm. This spike is called a ‘triple body scatter spike’, or colloquially as a hail spike.
Storms with that hail spike usually have either huge amounts of small hail or, more frequently, very very large hail. In the case of the storms last evening the supercell thunderstorm with a notable triple body scatter spike – or TBSS – produce nearly baseball size hail as it rumbled over Goldthwaite, Texas.
It’s a strange feature that has an even more fascinating formation method. Radar works by sending a beam of radio-waves and ‘listening’ for the ‘echo’ that bounces off of objects in range. The larger the object the more radar beam is reflected back.
This is why a very heavy rain shower shows up as reds and oranges and light rain is more of a pale green. The time the beam takes to return indicates how far from the radar site (since the speed of light is known and distance = velocity x time).
Hail is no different. Hailstones are normally larger than rain and will show up as brighter colors. What can happen when hailstones get very large is the radar beam can bounce off the hailstone but not return to the radar. Instead, the radar beam reflects down to the ground beyond the storm, bounces off the ground, back to the hailstone and back to the radar.
In general, the larger the hail spike, the larger the hailstones. Though this can also depend on many other factors like how ‘shiny’ the ground is beyond the thunderstorm. If a lot of rain fell the ground can reflect more radar energy and the scatter spike will be larger and more prominent. It can also be very pronounced due to large amounts of small hail in the storm.
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