Hail spike
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A hail spike or three body scatter spike (TBSS) is an artifact on a
weather radar Weather radar, also called weather surveillance radar (WSR) and Doppler weather radar, is a type of radar used to locate precipitation, calculate its motion, and estimate its type (rain, snow, hail etc.). Modern weather radars are mostly pulse- ...
display indicative of large hail. 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 acoustic effect on the Earth's atmosphere, known as thunder. Relatively weak thunderstorms are some ...
, and away from the radar site.


Cause

Generally known as hail spikes, these are the result of energy from the radar hitting hail, or very heavy rain, 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 by 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. {{Clr


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 agency of the United States federal government that is tasked with providing weather forecasts, warnings of hazardous weather, and other weather-related products to organizations and the public for the ...
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 both the surface of the 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, altho ...
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 co ...
*
Severe weather terminology (United States) This article describes severe weather terminology used by the National Weather Service (NWS) in the United States. The NWS, a government agency operating as an arm of the National Oceanic and Atmospheric Administration (NOAA) branch of the United ...
*
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 s ...
* 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)