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A hail spike or three body scatter spike (TBSS) is an artifact on a
In rare cases more than one hail spike has been documented with a single storm in one volume scan. This indicates that more than one hail core exists in the same storm and far enough apart that each core can be sampled by the radar individually.
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Because of their observed accuracy in indicating large hail aloft, TBSS's are used operationally by the
Three-Body Scatter Spike course
by the National Weather Service Hail Radar meteorology Radar theory Severe weather and convection Scattering, absorption and radiative transfer (optics)
A hail spike or three body scatter spike (TBSS) is an artifact on a weather radar
A weather radar, also called weather surveillance radar (WSR) and Doppler weather radar, is a type of radar used to locate precipitation (meteorology), precipitation, calculate its motion, and estimate its type (rain, snow, hail etc.). Modern w ...
display indicative of large hail
Hail is a form of solid Precipitation (meteorology), precipitation. It is distinct from ice pellets (American English "sleet"), though the two are often confused. It consists of balls or irregular lumps of ice, each of which is called a hailsto ...
. They are identified by a spike of weak reflectivity
The reflectance of the surface of a material is its effectiveness in Reflection (physics), reflecting radiant energy. It is the fraction of incident electromagnetic power that is reflected at the boundary. Reflectance is a component of the respon ...
echoes that extend out from a thunderstorm
A thunderstorm, also known as an electrical storm or a lightning storm, is a storm characterized by the presence of lightning and its acoustics, acoustic effect on the Earth's atmosphere, known as thunder. Relatively weak thunderstorm ...
, and away from the radar site.
Cause
Generally known as hail spikes, these are the result of energy from the radar hitting hail, very heavy rain, or in extreme cases, debris being lofted by a tornado, and being reflected to the ground, where they reflect back to the hail and then to the radar as in the image on the left. This results in the radar picking up the energy from the multiple path at a later time than the energy that came back directly from the hail to the radar. Both are however on the same radial angle from the radar as the antenna did not have the time to turn significantly. The multipath echoes are then analyzed on the radar display as echoes extending in a radial direction behind the actual location of the hail/heavy rain core. The loss of energy due to multiple reflections means weaker return echoes. The hail spike region has thus comparatively quite weaker echoes than the echoes directly from the hail or heavy rain core. Since hail cores are most intense at higher elevations, hail spikes usually appear at the levels aloft that accompany the most intense hail. Because of this, hail spikes are usually not seen at lower elevations. Another restriction to detection is that the signal of the radar beam has to do multiple reflections, each time weakening it, and are therefore usually noticeable only in extremely large hailstone cases.Multiple TBSS Signatures
In rare cases more than one hail spike has been documented with a single storm in one volume scan. This indicates that more than one hail core exists in the same storm and far enough apart that each core can be sampled by the radar individually.
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Use in forecasting
Because of their observed accuracy in indicating large hail aloft, TBSS's are used operationally by the National Weather Service
The National Weather Service (NWS) is an Government agency, agency of the Federal government of the United States, United States federal government that is tasked with providing weather forecasts, warnings of hazardous weather, and other weathe ...
to identify thunderstorms that could likely produce large, severe hail. This would warrant the issuance of a severe thunderstorm warning or mention of large hail in a tornado
A tornado is a violently rotating column of air that is in contact with the surface of Earth and a cumulonimbus cloud or, in rare cases, the base of a cumulus cloud. It is often referred to as a twister, whirlwind or cyclone, although the ...
warning.
See also
*Convective storm detection
Convective storm detection is the meteorological observation, and short-term prediction, of deep moist convection (DMC). DMC describes atmospheric conditions producing single or clusters of large vertical extension clouds ranging from cumulus c ...
* Severe weather terminology (United States)
This article describes severe weather terminology used by the National Weather Service (NWS) in the United States, a government agency operating within the United States Department of Commerce, Department of Commerce as an arm of the National Oc ...
* Severe weather terminology (Canada)
This article describes severe weather terminology used by the Meteorological Service of Canada, a branch within Environment and Climate Change Canada. The article primarily describes various weather warnings, and their criteria. Related weather ...
* Tornado debris signature aka "debris spike"
References
External links
Three-Body Scatter Spike course
by the National Weather Service Hail Radar meteorology Radar theory Severe weather and convection Scattering, absorption and radiative transfer (optics)