The Cool-Season Tornadoes of California and Southern Australia

Barry N. Hanstrum Bureau of Meteorology, Perth, Western Australia, Australia

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Graham A. Mills Bureau of Meteorology Research Centre, Melbourne, Victoria, Australia

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Andrew Watson Bureau of Meteorology, Adelaide, South Australia, Australia

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John P. Monteverdi San Francisco State University, San Francisco, California

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Charles A. Doswell III NOAA/National Severe Storms Laboratory, Norman, Oklahoma

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Abstract

Examples of cool-season tornadic thunderstorms in California and southern Australia are examined. Almost one-half of the reported Australian tornadoes and the majority of those in California occur in the cool season. It is shown that in both areas the typical synoptic pattern shows an active midlatitude trough just upstream, with a strong jet streak aloft. In both areas the tornadic thunderstorms occur with weak to moderate levels of thermodynamic instability in the lower troposphere but with extremely high values of low-level positive and bulk shear. Statistical tests on null cases (nontornadic thunderstorms) in the Central Valley of California indicate that large values of 0–1-km shear provide a discriminator for more damaging (F1–F3) tornadoes, whereas bulk measures of buoyancy, such as CAPE, do not. Australian case studies and tornado proximity soundings show similar characteristics. A “cool-season tornadic thunderstorm potential” diagnostic for Australian conditions, based on regional NWP analyses and forecasts, is described. It identifies those locations at which negative 700-hPa surface lifted index, near-surface convergence, and surface–850 hPa shear >11 m s−1 are forecast to occur simultaneously, and it shows considerable potential as an objective alert for forecasters. During the winter of 1996, all nine occasions on which tornadoes were reported were successfully identified in 24-h forecasts. After a variety of assessments suggested the value of this diagnostic, and following positive forecaster feedback during preoperational trials, it became an operational forecast product in May of 2000.

Current affiliation: Cooperative Institute for Mesoscale Meteorological Studies, Norman, Oklahoma

Corresponding author address: Graham A. Mills, Bureau of Meteorology Research Centre, Box 1289K Melbourne, VIC 3001, Australia. Email: g.mills@bom.gov.au

Abstract

Examples of cool-season tornadic thunderstorms in California and southern Australia are examined. Almost one-half of the reported Australian tornadoes and the majority of those in California occur in the cool season. It is shown that in both areas the typical synoptic pattern shows an active midlatitude trough just upstream, with a strong jet streak aloft. In both areas the tornadic thunderstorms occur with weak to moderate levels of thermodynamic instability in the lower troposphere but with extremely high values of low-level positive and bulk shear. Statistical tests on null cases (nontornadic thunderstorms) in the Central Valley of California indicate that large values of 0–1-km shear provide a discriminator for more damaging (F1–F3) tornadoes, whereas bulk measures of buoyancy, such as CAPE, do not. Australian case studies and tornado proximity soundings show similar characteristics. A “cool-season tornadic thunderstorm potential” diagnostic for Australian conditions, based on regional NWP analyses and forecasts, is described. It identifies those locations at which negative 700-hPa surface lifted index, near-surface convergence, and surface–850 hPa shear >11 m s−1 are forecast to occur simultaneously, and it shows considerable potential as an objective alert for forecasters. During the winter of 1996, all nine occasions on which tornadoes were reported were successfully identified in 24-h forecasts. After a variety of assessments suggested the value of this diagnostic, and following positive forecaster feedback during preoperational trials, it became an operational forecast product in May of 2000.

Current affiliation: Cooperative Institute for Mesoscale Meteorological Studies, Norman, Oklahoma

Corresponding author address: Graham A. Mills, Bureau of Meteorology Research Centre, Box 1289K Melbourne, VIC 3001, Australia. Email: g.mills@bom.gov.au

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  • Anderson, R. K., and Veltishchev N. F. , Eds.,. . 1973: The Use of Satellite Pictures in Weather Analysis and Forecasting. World Meteorological Organization Tech. Note 124, 275 pp.

    • Search Google Scholar
    • Export Citation
  • Blier, W., and Batten K. A. , 1994: On the incidence of tornadoes in California. Wea. Forecasting, 9 , 301315.

  • Bourke, W., Hart T. , Steinle P. , Seaman R. , Embery G. , Naughton M. , and Rikus L. , 1995: Evolution of the Bureau of Meteorology's global assimilation and prediction system. Part 2: Resolution enhancements and case studies. Aust. Meteor. Mag., 44 , 1940.

    • Search Google Scholar
    • Export Citation
  • Brook, R. R., 1965: Tornado at Mandurah, 15 June 1964. Aust. Meteor. Mag., 13 ((50),) 2634.

  • Carbone, R. E., 1983: A severe frontal rainband. Part II: Tornado parent vortex circulation. J. Atmos. Sci., 40 , 26392654.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Clarke, R. H., 1962: Severe local wind storms in Australia. CSIRO Division of Meteorological Physics Tech. Paper 13, 56 pp. [Available from CSIRO Atmospheric Research, PMB 1, Aspendale, VIC 3195, Australia.].

    • Search Google Scholar
    • Export Citation
  • Davies-Jones, R. P., 1986: Tornado dynamics. Thunderstorm Morphology and Dynamics, E. Kessler, Ed., University of Oklahoma Press, 197–236.

    • Search Google Scholar
    • Export Citation
  • Doswell, C. A. I. I. I,, Davies-Jones R. , and Keller D. L. , 1990: On summary measures of skill in rare event forecasting based on contingency tables. Wea. Forecasting, 5 , 576585.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Doswell, C. A. I. I. I,, Brooks H. E. , and Maddox R. A. , 1996: Flash flood forecasting: An ingredients-based methodology. Wea. Forecasting, 11 , 560581.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Foley, G. R., and Hanstrum B. N. , 1990: Severe local wind storms over southwestern Australia during the cooler months. Proc. Second Australian Severe Thunderstorm Workshop, Melbourne, Victoria, Australia, Bureau of Meteorology, 42–68. [Available from Bureau of Meteorology, Box 1289K, Melbourne, VIC 3001. Australia.].

    • Search Google Scholar
    • Export Citation
  • Grazulis, T. P., 1993: Significant Tornadoes, 1680–1991. Environmental Films, 1326 pp.

  • Hanstrum, B. N., 1994: The Mandurah tornado of 21 September 1994. Proc. Fourth Australian Severe Thunderstorm Conf., Mount Macedon, Victoria, Australia, Bureau of Meteorology, 89–107. [Available from Bureau of Meteorology, Box 1289K, Melbourne, VIC 3001. Australia.].

    • Search Google Scholar
    • Export Citation
  • Hanstrum, B. N., Mills G. A. , and Watson A. , 1998: Australian cool season tornadoes. Part 1: Synoptic climatology. Preprints, 19th Conf. on Severe Local Storms, Minneapolis, MN, Amer. Meteor. Soc., 97–100.

    • Search Google Scholar
    • Export Citation
  • Hart, J. A., and Korotky W. D. , 1991: The SHARP Workstation v1.50. A skew-T/hodograph analysis and research program for IBM and compatible PCs. User's manual. NOAA/NWS Forecast Office, Charleston, WV, 62 pp.

    • Search Google Scholar
    • Export Citation
  • Johns, R. H., and Doswell III C. A. , 1992: Severe local storms forecasting. Wea. Forecasting, 7 , 588612.

  • Johns, R. H., Davies J. M. , and Leftwich P. W. , 1993: Some wind and instability parameters associated with strong and violent tornadoes. 2: Variations in the combinations of wind instability parameters. The Tornado: Its Structure, Dynamics, Prediction, and Hazards, Geophys. Monogr., No. 79, Amer. Geophys. Union, 583–590.

    • Search Google Scholar
    • Export Citation
  • Lipari, G. S., and Monteverdi J. P. , 2000: Convective and shear parameters associated with northern and central California tornadoes during the period 1990–94. Preprints, 20th Conf. on Severe Local Storms, Orlando, FL, Amer. Meteor. Soc., 518–521.

    • Search Google Scholar
    • Export Citation
  • McCarthy, D., Schaefer J. , and Kay M. , 1998: Watch verification at the Storm Prediction Center 1970–1997. Preprints, 19th Conf. on Severe Local Storms, Minneapolis, MN, Amer. Meteor. Soc., 603–606.

    • Search Google Scholar
    • Export Citation
  • McCaul, E. W. Jr,, 1991: Buoyancy and shear characteristics of hurricane-tornado environments. Mon. Wea. Rev., 119 , 19541978.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • McCaul, E. W. Jr,, . 1993: Observations and simulations of hurricane-spawned tornadoes. The Tornado: Its Structure, Dynamics, Prediction and Hazards, Geophys. Monogr., No. 79, Amer. Geophys. Union, 119–142.

    • Search Google Scholar
    • Export Citation
  • McCaul, E. W. Jr,, and Weisman M. L. , 1996: Simulations of shallow supercell storms in landfalling hurricane environments. Mon. Wea. Rev., 124 , 408429.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • McCaul, E. W. Jr,, . 2001: The sensitivity of simulated supercell structure and intensity to variations in the shapes of environmental buoyancy and shear profiles. Mon. Wea. Rev., 129 , 664687.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Mills, G. A., 1997: Studies of cva maxima south of Australia. Part I: A long-lived enhanced cumulus signature and induced cyclogenesis. Aust. Meteor. Mag., 46 , 87107.

    • Search Google Scholar
    • Export Citation
  • Monteverdi, J. M., and Quadros J. , 1994: Convective and rotational parameters associated with three tornado episodes in northern and central California. Wea. Forecasting, 9 , 285300.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Monteverdi, J. M., and Johnson S. , 1996: A supercell with hook echo in the San Joaquin valley of California. Wea. Forecasting, 11 , 246261.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Ostby, F. P., 1992: Operations of the National Severe Storms Forecast Center. Wea. Forecasting, 7 , 546563.

  • Phillips, E. F., 1965: The Nurmurkah tornado of August 1964. Aust. Meteor. Mag., 13 ((48),) 3745.

  • Puri, K., Dietachmeyer G. D. , Mills G. A. , Davidson N. E. , Bowen R. A. , and Logan L. W. , 1998: The new BMRC Limited Area Prediction System, LAPS. Aust. Meteor. Mag., 47 , 203223.

    • Search Google Scholar
    • Export Citation
  • Ramage, C. S., 1962: The subtropical cyclone. J. Geophys. Res., 67 , 14011411.

  • Reed, R. J., and Blier W. , 1986: A further study of comma cloud development in the eastern Pacific. Mon. Wea. Rev., 114 , 16961708.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Rotunno, R., and Klemp J. B. , 1982: The influence of shear-induced pressure gradient on thunderstorm motion. Mon. Wea. Rev., 110 , 136151.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Trier, S. B., and Parsons D. B. , 1995: Updraft dynamics within a numerically simulated subtropical rainband. Mon. Wea. Rev., 123 , 3958.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Watson, A., 1985: An examination of three winter tornadoes in southwest Western Australia. Meteorological Note 162, Bureau of Meteorology, 43pp. [Available from Bureau of Meteorology, Box 1289K, Melbourne, VIC 3001, Australia.].

    • Search Google Scholar
    • Export Citation
  • Watson, A., . 1996: The tornado outbreak of 21 July 1995—Boundary layer vorticity and storm relative helicity influences. Proc. Fifth Australian Severe Thunderstorm Conf., Avoca Beach, New South Wales, Australia, Bureau of Meteorology, 53–57. [Available from Bureau of Meteorology, Box 1289K, Melbourne, VIC 3001, Australia.].

    • Search Google Scholar
    • Export Citation
  • Wicker, L. J., and Cantrell L. , 1996: The role of vertical buoyancy distributions in miniature supercells. Preprints, 18th Conf. on Severe Local Storms, San Francisco, CA, Amer. Meteor. Soc., 225–229.

    • Search Google Scholar
    • Export Citation
  • Young, M. V., 1995: Depressions in mid-latitudes. Images in Weather Forecasting, M. J. Bader et al., Eds., Cambridge University Press, 206–286.

    • Search Google Scholar
    • Export Citation
  • Zillman, J. W., 1962: Report on tornado investigation—Port Macquarie, July 1962. Aust. Meteor. Mag., 10 ((39),) 2848.

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