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Abstract Tornado motion changes occurring with major internal rear-flank momentum surges are examined in three significant tornado-producing supercells. The analysis primarily uses fixed-site Doppler radar data, but also utilizes in situ and videographic observations when available. In the cases examined, the peak lowest-level remotely sensed or in situ rear-flank surge wind speeds ranged from 48 to at least 63 m s −1 . Contemporaneous with major surges impacting the tornadoes and their parent low-level mesocyclones, longer-duration tornado heading changes were leftward and ranged from 30° to 55°. In all cases, the tornado speed increased substantially upon surge impact, with tornado speeds approximately doubling in two of the events. A storm-relative change in the hook echo orientation accompanied the major surges and provided a signal that a marked leftward heading change for an ongoing tornado was under way. Concurrent with the surge interaction, the hook echo tip and associated low-level mesocyclone turned leftward while also moving in a storm-relative downshear direction. The major rear-flank internal surges influenced tornado motion such that a generally favorable storm updraft-relative position was maintained. In all cases, the tornado lasted well beyond (≥21 min) the time of the surge-associated left turn with no evident marked loss of intensity until well down-track of the turn. The local momentum balance between outflow and inflow that bounds the tornado or its parent circulation, especially the directionality evolution of the bounding momentum, is the most apparent explanation for tornado down-track or off-track accelerations in the featured events.
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Environmental Conditions Associated with Long-Track Tornadoes
Abstract Reanalysis proximity vertical profile attributes associated with long-track tornadoes [LTTs; pathlength ≥ 48 km (30 mi)] and short-track tornadoes [STTs; pathlengths < 48 km (30 mi)] for a total of 48 212 tornadoes with pathlengths ≥ 0.016 km (0.01 mi) from 1979 to 2022 in the United States were examined. Both longer- and shorter-track tornadoes were associated with vast ranges of mixed-layer convective available potential energy, together with relatively low mixed-layer lifted condensation level heights and minimal convective inhibition. A large range of 500–9000-m wind speeds and bulk wind differences, 500–3000-m streamwise vorticities, storm-relative helicities, and storm-relative wind speeds were found for STTs. In stark contrast, LTTs only occurred when these kinematic attributes were larger in amplitude through the troposphere, supporting previously documented associations between observed longer-track tornado pathlengths and faster-propagating parent storms. A novel parameter, heavily weighted by kinematic parameters and lightly weighted by thermodynamic parameters, outperformed the significant tornado parameter in differentiating environments that were more supportive of both LTTs and tornadoes rated R2= 0.79 between tornado pathlength and Bunkers’ approximate tornado duration (pathlength/VBunkers) call for improved understanding of mesocyclone periodicities, which impact tornado longevity, to improve tornado pathlength diagnoses and forecasts. Pragmatically, diagnosing LTT environments using vertical profile attributes, perhaps, is not so much a problem of determining when there might be higher expectations for LTTs, but rather a problem of when there might be lower expectations for LTTs, e.g., weaker kinematic attributes in the lower troposphere. Significance StatementThe majority of tornadoes have pathlengths less than a few kilometers. As tornado pathlengths increase, their probability of causing impacts to society also increases. We study >40 years of modeled atmospheric vertical profiles to better understand the environmental conditions that support long-track tornadoes (pathlength ≥ 48 km or ≥30 mi). Consistent with previous studies, long-track tornadoes occurred with substantially stronger vertical wind shear profiles and low-level winds compared to short-track tornadoes; however, most tornadoes did not form in environments with exceedingly large vertical instability, regardless of pathlength or intensity. A proposed composite long-track tornado parameter (LTTP) provided better discrimination between longer and shorter pathlength events compared to preexisting parameters.
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- Award ID(s):
- 2048770
- PAR ID:
- 10562565
- Publisher / Repository:
- American Meteorological Society
- Date Published:
- Journal Name:
- Weather and Forecasting
- Volume:
- 40
- Issue:
- 1
- ISSN:
- 0882-8156
- Format(s):
- Medium: X Size: p. 3-35
- Size(s):
- p. 3-35
- Sponsoring Org:
- National Science Foundation
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