A mesocyclone is a meso-gamma mesoscale region of rotation (vortex), typically around 2 to 6 mi in diameter, most often noticed on radar within thunderstorms. In the northern hemisphere it is usually located in the right rear flank of a supercell, or often on the eastern, or leading, flank of a high-precipitation variety of supercell. The area overlaid by a mesocyclone’s circulation may be several miles (km) wide, but substantially larger than any tornado that may develop within it, and it is within mesocyclones that intense tornadoes form.
A tornado warning is a public warning that is issued by weather forecasting agencies to an area in the direct path of a tornado or a thunderstorm that is capable of producing a tornado. Modern weather surveillance technology such as Doppler weather radar allow for early detection of rotation in a thunderstorm, and for subsequent warnings to be issued before a tornado actually develops. It is nevertheless still not uncommon that warnings are issued based on reported visual sighting of a tornado, funnel cloud, or wall cloud, typically from weather spotters or the public, but also law enforcement or local emergency management. In particular, a tornado can develop in a gap of radar coverage, of which there are several known in the United States.
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 purposes of protection, safety, and general information. It is a part of the National Oceanic and Atmospheric Administration (NOAA) branch of the Department of Commerce, and is headquartered in Silver Spring, Maryland, within the Washington metropolitan area. The agency was known as the United States Weather Bureau from 1890 until it adopted its current name in 1970.
NEXRAD or Nexrad is a network of 159 high-resolution S-band Doppler weather radars operated by the National Weather Service (NWS), an agency of the National Oceanic and Atmospheric Administration (NOAA) within the United States Department of Commerce, the Federal Aviation Administration (FAA) within the Department of Transportation, and the U.S. Air Force within the Department of Defense. Its technical name is WSR-88D.
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. Modern weather radars are mostly pulse-Doppler radars, capable of detecting the motion of rain droplets in addition to the intensity of the precipitation. Both types of data can be analyzed to determine the structure of storms and their potential to cause severe weather.
A hook echo is a pendant or hook-shaped weather radar signature as part of some supercell thunderstorms. It is found in the lower portions of a storm as air and precipitation flow into a mesocyclone, resulting in a curved feature of reflectivity. The echo is produced by rain, hail, or even debris being wrapped around the supercell. It is one of the classic hallmarks of tornado-producing supercells. The National Weather Service may consider the presence of a hook echo coinciding with a tornado vortex signature as sufficient to justify issuing a tornado warning.
The National Severe Storms Laboratory (NSSL) is a National Oceanic and Atmospheric Administration (NOAA) weather research laboratory under the Office of Oceanic and Atmospheric Research. It is one of seven NOAA Research Laboratories (RLs).
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 States Department of Commerce (DoC), defines precise meanings for nearly all of its weather terms.
The bounded weak echo region, also known as a BWER or a vault, is a radar signature within a thunderstorm characterized by a local minimum in radar reflectivity at low levels which extends upward into, and is surrounded by, higher reflectivities aloft, forming a kind of dome of weak echoes. This feature is associated with a strong updraft and is almost always found in the inflow region of a thunderstorm: it cannot be seen visually. The BWER has been noted on radar imagery of severe thunderstorms since 1973 and has a lightning detection system equivalent known as a lightning hole.
ARMOR Doppler weather radar is a C-Band, Dual-Polarimetric Doppler Weather Radar, located at the Huntsville International Airport in Huntsville, Alabama. The radar is a collaborative effort between WHNT-TV and the University of Alabama in Huntsville. Live data for the radar is only available to a limited audience, such as UAH employees and NWS meteorologists. All ARMOR data is archived at the National Space Science and Technology Center located on the UAH campus.
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 congestus to cumulonimbus, the latter producing thunderstorms associated with lightning and thunder. Those two types of clouds can produce severe weather at the surface and aloft.
A tornadic vortex signature, abbreviated TVS, is a Pulse-Doppler radar weather radar detected rotation algorithm that indicates the likely presence of a strong mesocyclone that is in some stage of tornadogenesis. It may give meteorologists the ability to pinpoint and track the location of tornadic rotation within a larger storm, and is one component of the National Weather Service's warning operations.
The Baron Tornado Index (BTI), also called Vipir Tornado Index (VTI) is a meteorological computer model. Its main usage is to determine the probabilities of a tornado inside a Tornadic Vortex Signature on the rear flank of a storm, to better alert potential high-risk areas for tornadoes and to easily track them.
GRLevelX is a suite of data processing and display programs developed by Gibson Ridge Software, LLC (GRS), to view weather radar data. It went on the market in March 2005. It comes in three versions, all of which ingest raw data: GRLevel2 and GRLevel2 Analyst Edition for viewing Level II data of the National Weather Service (NWS), and GRLevel3 for viewing Level III data. All programs are capable of rendering dual polarization data.
Terminal Doppler Weather Radar (TDWR) is a Doppler weather radar system with a three-dimensional "pencil beam" used primarily for the detection of hazardous wind shear conditions, precipitation, and winds aloft on and near major airports situated in climates with great exposure to thunderstorms in the United States. As of 2011, all were in-service with 45 operational radars, some covering multiple airports in major metropolitan locations, across the United States & Puerto Rico. Several similar weather radars have also been sold to other countries such as China (Hong Kong). Funded by the United States Federal Aviation Administration (FAA), TDWR technology was developed in the early 1990s at Lincoln Laboratory, part of the Massachusetts Institute of Technology, to assist air traffic controllers by providing real-time wind shear detection and high-resolution precipitation data.
Baron Services is a weather technology company based in Huntsville, Alabama, United States. The company develops weather systems that aid in the detection and dissemination of weather information to customers in the broadcast, government, aviation, marine and automotive industries. These technologies include weather tracking software, Doppler weather radar, systems integration, and personal alerting services, among others. The company holds numerous U.S. patents for weather technology.
A line echo wave pattern (LEWP) is a weather radar formation in which a single line of thunderstorms presenting multiple bow echoes forms south of a mesoscale low-pressure area with a rotating "head". LEWP often are associated with a multiple-bow serial derecho and often produce tornadoes, some of which can be strong. The existence of a LEWP on radar means that a serial derecho has developed or is likely to develop soon, much as a hook echo indicates the same for a tornado.
Leslie R. Lemon was an American meteorologist bridging research and forecasting with expertise in weather radar, particularly regarding severe convective storms. Lemon was, along with Charles A. Doswell III, a seminal contributor to the modern conception of the supercell which was first identified by Keith Browning, and he developed the Lemon technique to estimate updraft strength and thunderstorm organization also as a continuation of Browning's work.
The following is a glossary of tornado terms. It includes scientific as well as selected informal terminology.
Multiple Elevation Scan Option for Supplemental Adaptive Intra-Volume Low-Level Scan, is a dynamic scanning option for the WSR-88D, controllable by the operator of the radar, when in VCP mode 12 and 212, and additionally 35 and 215 with the Build 18 update scheduled for October 2017. When active, anywhere from one to three supplemental low-level scans can be added to any volume, increasing overall low-level data availability and improves general severe weather detection, as needed. When active, per the National Weather Service, low-level updates will be available "every 75 to 90 seconds".