Glossary of tornado terms

The following is a glossary of tornado terms. It includes scientific as well as selected informal terminology.

A

Advanced Radar Research Center (ARRC) Advection Air parcel American Geophysical Union (AGU) American Meteorological Society (AMS) Anticipated convection (AC) – A convective outlook. Angular momentum Anticyclone Anticyclonic rotation Anticyclonic tornado Anticyclogenesis Arcus cloud Atmosphere Atmospheric pressure

B

Baroclinity or baroclinicity – baroclinic Barotropity or barotropicity – barotropic Bear's cage – (tornado chaser slang) The precipitation that wraps around a mesocyclone, possibly hiding a tornado on the ground. Beaufort scale Bernoulli's principle Blob – Informal term coined by Erik N. Rasmussen for a descending reflectivity core (DRC). Boundary Bounded weak echo region (BWER) Bow echo BRN shear Bulk Richardson Number (BRN) Bulk shear Buoyancy

C

Capping inversion (cap) Center for Analysis and Prediction of Storms (CAPS) Center for Severe Weather Research (CSWR) Chaser convention – Originally it referred to serendipitous meeting of chasers in the field akin to "chaser convergence", but now it mostly refers to the National Storm Chasers Convention held annually in the Denver, Colorado area. Cloud tag Cluster outbreak Cold air funnel – (colloquialism) Cold front Collar cloud Colorado low Cool air advection (CAA) Condensation funnel – The area of a funnel cloud or tornado where cloud has condensed. This is not the same thing as a tornado, which is a vortex of wind. Confluence Cooperative Institute for Mesoscale Meteorological Studies (CIMMS) – Cooperative Institute for Meteorological Satellite Studies (CIMSS) Cooperative Institute for Precipitation Systems (CIPS) Cooperative Institute for Research in the Atmosphere (CIRA) Convection Convective available potential energy (CAPE) Convective condensation level (CCL) Convective inhibition (CIN or CINh) Convective instability Convective outlook Convective storm Convective storm detection Convective storm prediction Convective temperature (CT or Tc) Convergence Core Core flow region Core punching (or punching the core) Corridor outbreak Cumulonimbus cloud (Cb) Cycloidal marks Cyclonic rotation Cyclogenesis Cyclone – An area of cyclonic low pressure, from the scale of an extratropical or tropical cyclone to mesolow to a mesocyclone to a tornadocyclone or even to a tornado. – (slang) Historically, used in the US to a tornado.

D

Damage survey DAPPL database – Short for Damage Area Per Path Length, this is one of three US tornado databases and was maintained by Ted Fujita at the University of Chicago including tornadoes from 1916 to 1992. Debris cloud Deepening low Deep convection Deep shear Denver Convergence Vorticity Zone (DCVZ) Derecho Descending reflectivity core (DRC) Dew point (Td) Dew point depression Dewpoint surge line Diffluence – A pattern of wind flow in which air moves outward (in a "fan-out" pattern) away from a central axis that is oriented parallel to the general direction of the flow. It is the opposite of confluence.Weather Glossary for Storm Chasers Digging low or digging wave Direct hit Directional shear Divergence Doppler on Wheels (DOW) Doppler weather radar Dry convection (or dry mixing) – A vertical exchange of air without precipitation at the ground. Dry line (DL) Dryline bulge Dry punch Dry thunderstorm Dust devil Downburst Downdraft

E

Earth System Research Laboratories (ESRL) Eddy Elevated mixed layer (EML) Energy-helicity index (EHI) Energy scale (E scale) – Wind speed scales proposed by Nikolai Dotzek for application to tornadoes, downbursts, tropical cyclones, other storms and wind in general.Tornado Terms – Tornado Terminology Enhanced Fujita scale (EF-scale) Enhanced wording Entrainment Environment and Climate Change Canada Environmental Modeling Center (EMC) Environmental Research Laboratories (ERL) Environmental Science Services Administration (ESSA) – The predecessor agency (1965–1970) to NOAA (1970–present). Equivalent potential temperature (theta-e) Extratropical cyclone Eye of a tropical cyclone

F

Filling low Fire whirl Forecast Decision Training Branch (FDTB) Forecast Systems Laboratory (FSL) Forward-flank downdraft (or front-flank downdraft) (FFD) Fractus cloud (Fr) Front Frontogenesis Fujita scale (F–scale) Funnel cloud

G

Gate-to-gate shear GMT (Greenwich Mean Time) Ground truth Gust front Gustnado

H

Handoff – (slang) Helicity High-precipitation supercell (HP) High-pressure area (H) High risk (HIGH) Hook echo Horseshoe vortex Hurricane

I

In situ Inflow Inflow jet Inflow notch Instability Intense tornado – A tornado rated F3–F5 or EF3–EF5. Institute for Disaster Research (IDR)

J

Jet max (or jet maximum) Jet streak Jet stream

K

Kinematics K-index Kelvin–Helmholtz instability (KH waves)

L

Landspout Lapse rate Lee trough Lemon technique Level of free convection (LFC) Lifted condensation level (LCL) Lifted index (LI) Lifting mechanism (lift) Lightning (LTG) Line echo wave pattern (LEWP) Long track tornado (LT) Low-precipitation supercell (LP) Low-pressure area (L) Low-topped supercell (LT)

M

Maxitornado Megasupercell Mesoanticyclone – An anticyclonic mesocyclone Mesoscale meteorology Mesocyclone Mesohigh Mesolow Mesonet Mesoscale convective complex (MCC) Mesoscale convective discussion (MCD) Mesoscale convective system (MCS) Mesoscale convective vortex (MCV) Mesoscale meteorology Mesovortices Metadata METAR Microburst Micronet – A weather observation network even denser than a mesonet, such as the Oklahoma City Micronet. Microscale meteorology Mini-supercell – A distinct kind of supercell that is smaller than a typical supercell. See low topped supercell. Mini-tornado – A fallacious term often used in European news media to refer to tornadoes occurring there; even large, strong, and/or long track tornadoes produced by supercells. This is apparently due to the erroneous perception that "real" tornadoes do not occur in Europe (or elsewhere where the term is applied). Misocyclone Misoscale meteorology Mixed air and mixed layer Mixing ratio Moderate risk (MDT) Modified Fujita scale (f scale) – A proposed update in 1992 by Ted Fujita to his original Fujita scale from 1971 Moisture Moisture convergence (mcon) Multicellular thunderstorm Multiple-vortex tornado Multivortex mesocyclone (MVMC)

N

National Center for Atmospheric Research (NCAR) National Centers for Environmental Prediction (NCEP) National Hurricane Center (NHC) National Meteorological Center (NMC) – The predecessor to NCEP. National Oceanic and Atmospheric Administration (NOAA) National Science Foundation (NSF) National Severe Storms Forecast Center (NSSFC) – A predecessor forecasting center to SPC that was located in Kansas City, Missouri. National Severe Storms Laboratory (NSSL) – A NOAA lab in Norman, Oklahoma tasked with researching severe weather. National Tornado Database – The official NOAA record of all known tornadoes within the US from 1950 to present. National Weather Center (NWC) National Weather Service (NWS) National Weather Service Training Center (NWSTC) National Wind Institute (NWI) Negative area Negatively tilted (or negative tilt)

O

Occluded front Occlusion Overshooting top Outflow Outflow boundary

P

Particularly Dangerous Situation (PDS) Path length (Pl) – The distance a tornado traveled from formation to decay. Path width (Pw) – The diameter of the tornado vortex winds (not the condensation funnel) capable of causing damage. Pearson scale (or Fujita-Pearson scale) – A tornado rating scale developed by Allen Pearson differentiating path length (P) and path width (P) to accompany NOAA Fujita scale (F) ratings (F-P-P scale). Pendant Phased array radar Positive area Potential temperature () Power flash – A sudden bright light caused when an overhead power line is severed or especially when a transformer explodes. These can be caused by intense winds (or debris) from tornadoes or downbursts, but the most prominent example occurred in New York City during Hurricane Sandy when its storm surge flooded a Con Ed power plant. Precipitable water Prefrontal trough Pressure falls Pressure gradient Pressure gradient force (PGF) Pressure system Probe PROFS (Prototype Regional Observing and Forecasting Service) Pulse-Doppler radar Pulse storm

Q

Quasi-linear convective system (QLCS)

R

Radar Operations Center (ROC) Radius of maximum wind (RMW) Rain-free base (RFB) Rankine vortex Rear flank downdraft (RFD) Ridge Roll cloud Remote sensing Rope tornado Rossby number Rossby wave Rotation

S

Safe room Satellite tornado – A smaller tornado that orbits a primary tornado associated with the same mesocyclone. Scouring – Term used when soil and dirt is pulled from the surface after a tornado. Scud (Scattered Cumulus Under Deck) Severe local storm (SLS) – A thunderstorm presenting severe characteristics in a localized area. Severe Local Storms Unit (SELS) – A team of National Weather Service experts tasked with forecasting convective weather. It was eventually included as a unit within the NSSFC. Severe thunderstorm (svr) – A hazardous thunderstorm capable of causing injury or damage. The U.S. National Weather Service defines a severe thunderstorm as one producing or greater winds, or larger hail, or producing a funnel cloud or tornado. Shallow convection – Occurs when convective instability exists, but no convection occurs Shear – Wind shear – Winds aloft, often measured in knots. Shear funnel – Brief, often weak funnel generated by shear in a thunderstorm. Shelf cloud – Generally associated with strong thunderstorms, found along the leading edge. Horizontal and dark in appearance. Shortwave trough – Embedded kink within seen in overall troughing patterns. Significant tornado – A substantial tornado, one that is rated F2–F5 or EF2–EF5. Grazulis also includes (E)F0–(E)F1 tornadoes that cause a fatality in his definition for The Tornado Project database. Significant tornado parameter (STP) – Model parameter calculated using shear values, Instability values, and vorticity values. Skipping tornado – Often considered a Multi-vortex tornado. Skywarn – The storm spotting program of the US National Weather Service. Skywarn organizations have also been formed in Europe. The Canadian program is Canwarn. Slight risk (SLGT) Space Science and Engineering Center (SSEC) Speed shear Spin-up – A small, ephemeral vortex. These can refer to tornadoes spawned by quasi-linear convective systems or tropical cyclones, which occasionally become strong and fairly long track. A spin-up may sometimes refer to a landspout or gustnado (the latter of which is rarely an actual tornado). Splitting storm (or storm split) Stability index Stacked low Steam devil Storm chasing – Traveling with the intent to observe tornadoes and other severe weather. Storm interaction Storm merger Storm relative environmental helicity (SREH) or storm relative helicity (SRH) Storm shelter Storm spotting – The observation of severe weather by individuals trained in weather and reporting. Spotters can be stationary or mobile. Storm Data (SD) – A National Climatic Data Center (NCDC) publication beginning in 1959 detailing quality controlled tornado and other severe weather summaries as the official NOAA record of such events. Storm Prediction Center (SPC) – The NWS national guidance center that issues tornado, severe thunderstorm (straight-line wind and hail), and wildfire forecasts. Storm scale Storm Track (magazine) (ST) – A science and hobby magazine on storm chasing published from 1977 to 2002. Stovepipe tornado – (slang) Storm chaser slang for a large cylindrically shaped tornado resembling a stovepipe. Straight-line wind