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focus of the research com- munity ( e.g., Browning 1964; Lemon and Doswell 1979; Klemp 1987) , other studies have acknowledged the generally weaker, but occasionally quite damaging, nonsupercell tornadic storm ( e.g., Wakimoto and Wil- son 1989) . Although many questions with regard to the devel- opment and evolution of tornadoes remain unresolved, much has been learned about the storm-scale processes leading to tornadogenesis since the Thunderstorm Pro- ject ( Byers and Braham 1949) , the first
focus of the research com- munity ( e.g., Browning 1964; Lemon and Doswell 1979; Klemp 1987) , other studies have acknowledged the generally weaker, but occasionally quite damaging, nonsupercell tornadic storm ( e.g., Wakimoto and Wil- son 1989) . Although many questions with regard to the devel- opment and evolution of tornadoes remain unresolved, much has been learned about the storm-scale processes leading to tornadogenesis since the Thunderstorm Pro- ject ( Byers and Braham 1949) , the first
vector magnitude did not. These and other studies (e.g., Kerr and Darkow 1996 ; Rasmussen and Blanchard 1998 ; Monteverdi et al. 2003 ) emphasize the important point that severe thunderstorm and tornadoes occur within a broad range of shear and CAPE environments. It is extremely important to keep in mind that it is likely the interaction of a number of physical processes that leads to tornadogenesis, and these processes may (or may not) be well represented by particular environmental parameters or
vector magnitude did not. These and other studies (e.g., Kerr and Darkow 1996 ; Rasmussen and Blanchard 1998 ; Monteverdi et al. 2003 ) emphasize the important point that severe thunderstorm and tornadoes occur within a broad range of shear and CAPE environments. It is extremely important to keep in mind that it is likely the interaction of a number of physical processes that leads to tornadogenesis, and these processes may (or may not) be well represented by particular environmental parameters or
of the environmental parameters associated with an environment conducive to tornadogenesis. We know that the combination of 0–6-km vector shear magnitude (SHR6, the magnitude of the vector difference in winds between the surface and 6-km height) and mixed-layer convective available potential energy (MLCAPE) provides a good first estimate of supercell potential ( Brooks et al. 2003 ), with at least marginal CAPE necessary to fuel the updraft and SHR6 essential for developing the midlevel rotation
of the environmental parameters associated with an environment conducive to tornadogenesis. We know that the combination of 0–6-km vector shear magnitude (SHR6, the magnitude of the vector difference in winds between the surface and 6-km height) and mixed-layer convective available potential energy (MLCAPE) provides a good first estimate of supercell potential ( Brooks et al. 2003 ), with at least marginal CAPE necessary to fuel the updraft and SHR6 essential for developing the midlevel rotation
tornadogenesis (e.g., McCaul 1987 ; Spratt et al. 1997 ; Suzuki et al. 2000 ; McCaul et al. 2004 ; Edwards 2008 ). However, these TC-related supercells often are shallower and smaller than their midlatitude counterparts ( McCaul and Weisman 1996 ). These differences must be considered when forecasting TC-related tornadoes. The magnitude of instability (e.g., CAPE) appears to be less important in TC-related tornadoes than in midlatitude scenarios. Indeed CAPE typically is observed to be considerably
tornadogenesis (e.g., McCaul 1987 ; Spratt et al. 1997 ; Suzuki et al. 2000 ; McCaul et al. 2004 ; Edwards 2008 ). However, these TC-related supercells often are shallower and smaller than their midlatitude counterparts ( McCaul and Weisman 1996 ). These differences must be considered when forecasting TC-related tornadoes. The magnitude of instability (e.g., CAPE) appears to be less important in TC-related tornadoes than in midlatitude scenarios. Indeed CAPE typically is observed to be considerably
radar scans collected by the Jackson, Mississippi (KJAN), Weather Surveillance Radar-1988 Doppler (WSR-88D; see Trapp et al. 1999 ). Hence, as in the other cases of QLCS tornadoes preliminarily investigated by Trapp et al. (1999) , traditional radar-based indicators of impending tornadogenesis likely offered little operational tornado-warning guidance for this event. And since this example (which is one of several) of QLCS tornado occurrence happened during the overnight hours, guidance from storm
radar scans collected by the Jackson, Mississippi (KJAN), Weather Surveillance Radar-1988 Doppler (WSR-88D; see Trapp et al. 1999 ). Hence, as in the other cases of QLCS tornadoes preliminarily investigated by Trapp et al. (1999) , traditional radar-based indicators of impending tornadogenesis likely offered little operational tornado-warning guidance for this event. And since this example (which is one of several) of QLCS tornado occurrence happened during the overnight hours, guidance from storm
anticipate intelligently storm evolution and threat and therefore the range of potential outcomes necessary to determine warning content. For example, a tornado is more likely to occur with a classic supercell than a bowing squall line, where damaging wind is often the primary threat. Consider the case of the collapsing supercell: the disappearance of the reflectivity hook and lowering of the storm top could suggest a weakening storm, or, in the eyes of an expert, it might signal tornadogenesis ( Lemon
anticipate intelligently storm evolution and threat and therefore the range of potential outcomes necessary to determine warning content. For example, a tornado is more likely to occur with a classic supercell than a bowing squall line, where damaging wind is often the primary threat. Consider the case of the collapsing supercell: the disappearance of the reflectivity hook and lowering of the storm top could suggest a weakening storm, or, in the eyes of an expert, it might signal tornadogenesis ( Lemon
versus tornado count–tornado days As illustrated by Dixon and Mercer (2012) , large differences in spatial patterns can occur if one uses point analysis [i.e., the point of tornadogenesis; e.g., Brooks et al. (2003) ] instead of pathlength analysis (e.g., Dixon et al. 2011 ). Given that the pathlength of a tornado is much more proportional to the area it affects, its destructive capability, and its overall impact on the risk of a tornado striking an area within its radius of influence in the KDE
versus tornado count–tornado days As illustrated by Dixon and Mercer (2012) , large differences in spatial patterns can occur if one uses point analysis [i.e., the point of tornadogenesis; e.g., Brooks et al. (2003) ] instead of pathlength analysis (e.g., Dixon et al. 2011 ). Given that the pathlength of a tornado is much more proportional to the area it affects, its destructive capability, and its overall impact on the risk of a tornado striking an area within its radius of influence in the KDE
strong azimuthal velocity gradient was observed coincident with the developing hook echo. Later, the first pulsed Doppler radar observation of a tornado was made during the Brookline, Massachusetts, tornado on 9 April 1972 ( Kraus 1973 ). Interestingly, no hook echo was observed at the time of the tornado; however, a hook echo was observed prior to tornadogenesis. In 1973, the National Severe Storms Laboratory’s 10-cm pulsed Doppler radar scanned through a tornadic thunderstorm near Union City
strong azimuthal velocity gradient was observed coincident with the developing hook echo. Later, the first pulsed Doppler radar observation of a tornado was made during the Brookline, Massachusetts, tornado on 9 April 1972 ( Kraus 1973 ). Interestingly, no hook echo was observed at the time of the tornado; however, a hook echo was observed prior to tornadogenesis. In 1973, the National Severe Storms Laboratory’s 10-cm pulsed Doppler radar scanned through a tornadic thunderstorm near Union City
discriminating between tornadic and nontornadic thunderstorm environments ( Weisman and Klemp 1982 ; Stensrud et al. 1997, hereafter SCB97 ). In the BRN denominator, as calculated by SCB97, U avg is defined as the magnitude of the difference between the 0–6-km density-weighted mean wind and the density-weighted mean wind in the lowest 0.5 km: BRN shear = 0.5( u avg ) 2 . Numerical simulations of supercells have begun to elucidate processes relevant to supercell tornadogenesis, and the
discriminating between tornadic and nontornadic thunderstorm environments ( Weisman and Klemp 1982 ; Stensrud et al. 1997, hereafter SCB97 ). In the BRN denominator, as calculated by SCB97, U avg is defined as the magnitude of the difference between the 0–6-km density-weighted mean wind and the density-weighted mean wind in the lowest 0.5 km: BRN shear = 0.5( u avg ) 2 . Numerical simulations of supercells have begun to elucidate processes relevant to supercell tornadogenesis, and the
below 3 km after 0030 UTC 25 June, during which time 32 tornadoes occurred. In addition, tornadoes in this region showed a general increase in damage rating with time, with the most damaging tornadoes occurring after 0100 UTC 25 June. Supercells also developed along the cold front in sector 3 and also were responsible for tornadoes. This would be the source region for a quasi-linear convective system (QLCS) that later produced tornadoes in sector 2. Fig . 1. Sectors for mode of tornadogenesis with
below 3 km after 0030 UTC 25 June, during which time 32 tornadoes occurred. In addition, tornadoes in this region showed a general increase in damage rating with time, with the most damaging tornadoes occurring after 0100 UTC 25 June. Supercells also developed along the cold front in sector 3 and also were responsible for tornadoes. This would be the source region for a quasi-linear convective system (QLCS) that later produced tornadoes in sector 2. Fig . 1. Sectors for mode of tornadogenesis with
