Background Material

Supercell motion has remained an interesting topic since the 1940s when the documentation of these storms was in its infancy. The feature that sets supercells apart from ordinary thunderstorms is the presence of deep and persistent rotation (counterclockwise for right-moving storms and clockwise for left-moving storms, irrespective of hemisphere). Note that right-/left-moving is relative to the hodograph (i.e., shear). This rotation induces a propagation component that is at right angles to the vertical wind shear (and not the mean wind). This sometimes leads to a supercell motion that is at significant angles to the mean wind, and in a few instances, supercells have been observed to move "upstream" against the mean flow. As a result of these observations, and along with inspiration from the COMET module, "Anticipating Convective Storm Structure and Evolution," we began research in 1996 to further study the behavior of supercell motion, with a goal of being able to better predict supercell motion prior to storm formation. Our results support many of the previous theoretical and modeling studies, which indicate that supercell motion is primarily determined by advection plus rotationally induced propagation across the vertical wind shear. Studies by Ramsay and Doswell (2005) and Thomson et al. (2007) have supported our work. We also note that thermodynamics may modulate supercell motion, and recent modeling work sheds some light on this topic (Kirkpatrick et al. 2007). After completing the above storm motion project, we looked at the vertical wind shear in environments of both right- and left-moving supercells (Bunkers 2002). We found that the bulk and total wind shear are similar for the two classes, but the absolute value of storm-relative helicity is larger for right-moving supercells, relative to the left-movers, across the United States. Additional work includes an understanding of supercell longevity as well as an assessment of supercell motion forecast errors under varying environmental and storm constraints.

Hodographs & 2005 Virtual Institute for Satellite Integration Training (VISIT) Teletraining

a) Supercell Motion Teletraining (includes audio playback version)
b) Predicting Supercell Motion in Operations (standalone PPT)

Formal Publications

• Bunkers, M. J., 2002: Vertical wind shear associated with left-moving supercells. Wea. Forecasting, 17, 845–855.
• Bunkers, M. J., 2009: Comments on "Observational Analysis of the Predictability of Mesoscale Convective Systems." Wea. Forecasting, 24, 351–355.
• Bunkers, M. J., 2018: Observations of right-moving supercell motion forecast errors. Wea. Forecasting, 33, 145–159.
• Bunkers, M. J., and J. W. Stoppkotte, 2007: Documentation of a rare tornadic left-moving supercell. Electronic J. Severe Storms Meteor., 2 (2), 1–22, https://doi.org/10.55599/ejssm.v2i2.7.
• Bunkers, M. J., M. S. Van Den Broeke, and J. T. Allen, 2024: An update for predicting left-moving supercell motion. Wea. Forecasting, 39, 1777–1794.
• Bunkers, M. J., and M. A. Baxter, 2011: Radar tornadic debris signatures on 27 April 2011. Electronic J. Operational Meteor., 12 (7), 1–6.
• Bunkers, M. J., and C. A. Doswell III, 2016: Comments on “Double Impact: When Both Tornadoes and Flash Floods Threaten the Same Place at the Same Time.” Wea. Forecasting, 31, 1715-1721.
• Bunkers, M. J., B. A. Klimowski, J. W. Zeitler, R. L. Thompson, and M. L. Weisman, 2000: Predicting supercell motion using a new hodograph technique. Wea. Forecasting, 15, 61–79.
• Bunkers, M. J., M. R. Hjelmfelt, and P. L. Smith, 2006a: An observational examination of long-lived supercells. Part I: Characteristics, evolution, and demise. Wea. Forecasting, 21, 673–688.
• Bunkers, M. J., J. S. Johnson, L. J. Czepyha, J. M. Grzywacz, B. A. Klimowski, and M. R. Hjelmfelt, 2006b: An observational examination of long-lived supercells. Part II: Environmental conditions and forecasting. Wea. Forecasting, 21, 689–714.
• Bunkers, M. J., D. R. Clabo, and J. W. Zeitler, 2009: Comments on "Structure and Formation Mechanism on the 24 May 2000 Supercell-Like Storm Developing in a Moist Environment over the Kanto Plain, Japan." Mon. Wea. Rev., 137, 2703–2712.
  • * Corrigendum (8/26/2011): Although not our intention, there are a few places in the paper (e.g., p. 2704) where vertical vorticity and azimuthal shear were inadvertently commingled. This is inappropriate because for solid body rotation the vertical vorticity equals twice the azimuthal shear; they are not equal to each other as implied on p. 2704. Thus, if vertical vorticity = 1 *10^-2 s^-1, then the azimuthal shear = 0.5 *10^-2 s^-1. Accordingly, the lower bounds of vertical vorticity in Table 1 should be 0.6–1.0 *10 ^-2 s^-1. Nevertheless, the main conclusion that the Kanto Plain storm was a supercell remains valid.
• Bunkers, M. J., D. A. Barber, R. L. Thompson, R. Edwards, and J. Garner, 2014: Choosing a universal mean wind for supercell motion prediction. J. Operational Meteor., 2 (11), 115–129, https://dx.doi.org/10.15191/nwajom.2014.0211.
• Bunkers, M. J., M. B. Wilson, M. S. Van Den Broeke, and D. J. Healey, 2022: Scan-by-scan storm-motion deviations for concurrent tornadic and nontornadic supercells. Wea. Forecasting, 37, 749–770, https://doi.org/10.1175/WAF-D-21-0153.1.
• Klimowski, B. A., and M. J. Bunkers, 2002: Comments on “Satellite observations of a severe supercell thunderstorm on 24 July 2000 made during the GOES-11 science test.” Wea. Forecasting, 17, 1111–1117.
• Klimowski, B. A., M. R. Hjelmfelt, M. J. Bunkers, D. Sedlacek, and L. R. Johnson, 1998: Hailstorm damage observed from the GOES-8 satellite: The 5-6 July 1996 Butte–Meade storm. Mon. Wea. Rev., 126, 831–834.
• Klimowski, B. A., M. J. Bunkers, M. R. Hjelmfelt, and J. N. Covert, 2003: Severe convective windstorms over the northern high plains of the United States. Wea. Forecasting, 18, 502–519.
• Klimowski, B. A., M. R., Hjelmfelt, and M. J. Bunkers, 2004: Radar observations of the early evolution of bow echoes. Wea. Forecasting, 19, 727–734.
• Lindsey, D. T., and M. J. Bunkers, 2005: Observations of a severe, left-moving supercell on 4 May 2003. Wea. Forecasting, 20, 15–22.
• Nixon, C. J., J. T. Allen, M. B. Wilson, M. J. Bunkers, and M. Taszarek, 2024: Cell mergers, boundary interactions, and convective systems in cases of significant tornadoes and hail. Wea. Forecasting, 39, 1435–1458.
• Zeitler, J. W., and M. J. Bunkers, 2005: Operational forecasting of supercell motion: Review and case studies using multiple datasets. Natl. Wea. Dig., 29 (1), 81–97.

Informal Publications

• Bunkers, M. J., 1996a: Examination of the preconvective environment associated with a severe nontornadic supercell: Variations in CAPE and SREH. Preprints, 18^th Conf. on Severe Local Storms, San Francisco, CA, Amer. Meteor. Soc., 703–707.
• Bunkers, M. J., 1996b: On the use of the WSR-88D during situations of rapidly developing severe thunderstorms. NOAA/NWS WFO Rapid City, SD , Internal Report, 6 p.
• Bunkers, M. J., 2002: A new convective sounding analysis program for AWIPS. Preprints, 18^th International Conference on Interactive Information and Processing Systems (IIPS), Orlando, FL, Amer. Meteor. Soc., 209–210.
• Bunkers, M. J., 2006: An observational assessment of off-hodograph deviations for use in operational supercell motion forecasting methods. Preprints, 23rd Conf. on Severe Local Storms, St. Louis, MO, Amer. Meteor. Soc., 8.6. 
• Bunkers, M. J., 2010: How midlevel horizontal humidity gradients affect simulated storm morphology. Preprints, 25th Conf. on Severe Local Storms, Denver, CO, Amer. Meteor. Soc., P7.1.
• Bunkers, M. J., and J. W. Zeitler, 2000: On the nature of highly deviant supercell motion. Preprints, 20^th Conf. on Severe Local Storms, Orlando, FL, Amer. Meteor. Soc., 236–239.
• Bunkers, M. J., B. A. Klimowski, J. W. Zeitler, R. L. Thompson, and M. L. Weisman, 1998: Predicting supercell motion using hodograph techniques. Preprints, 19^th Conf. on Severe Local Storms, Minneapolis, MN, Amer. Meteor. Soc., 611–614.
• Bunkers, M. J., B. A. Klimowski, and J. W. Zeitler, 2002: The importance of parcel choice and the measure of vertical wind shear in evaluating the convective environment. Preprints, 21^st Conf. on Severe Local Storms, San Antonio, TX, Amer. Meteor. Soc., 379–382.
• Bunkers, M. J., J. S. Johnson, J. M. Grzywacz, L. J. Czepyha, and B. A. Klimowski, 2002: A preliminary investigation of supercell longevity. Preprints, 21^st Conf. on Severe Local Storms, San Antonio, TX, Amer. Meteor. Soc., 655–658.
• Bunkers, M. J., M. Smith, D. Driscoll, and G. Hoogestraat, 2015: Hydrologic response for a high-elevation storm in the South Dakota Black Hills. NOAA/NWS Rapid City, SD, Internal Report 2015-01, 21 pp.
• Hintz, D. L., and M. J. Bunkers, 1995: Examination of an apparent landspout in the eastern Black Hills of western South Dakota. NOAA/NWS CR Tech. Attach. 95-08, 11 pp. [Available from NWS Central Region, 601 E. 12^th St., Rm 1836, Kansas City, MO 64106-2897.]
• Lindsey, D. T., and M. J. Bunkers, 2004: On the motion and interaction between left-moving and right-moving supercells on 4 May 2003. 22^nd Conf. on Severe Local Storms, Hyannis, MA, Amer. Meteor. Soc., CD-ROM, 12.2.
• Yu, X., M. A. Magsig, and M. J. Bunkers, 2002: Enhancements to a new convective sounding analysis program for AWIPS. Preprints, 21^st Conf. on Severe Local Storms, San Antonio, TX, Amer. Meteor. Soc., J77–J80.
• Zeitler, J. W., and M. J. Bunkers, 2002: Anticipating and monitoring supercell motion for severe weather operations. Preprints, 21^st Conf. on Severe Local Storms, San Antonio, TX, Amer. Meteor. Soc., J61–J64.