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Cool Season Tornadoes in the Southeast U.S.

Cool Season Tornadoes in the Southeast U.S. 28 December 2005. 11 November 2002. 2 January 2006. 15 November 2006. 25 December 2006. 31 December 2006. 7 January 2007. Steven Nelson Stephen Konarik WFO Peachtree City. 5 January 2007. 26 February 2008. 15 December 2007. 17 February 2008.

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Cool Season Tornadoes in the Southeast U.S.

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  1. Cool Season Tornadoes in the Southeast U.S. 28 December 2005 11 November 2002 2 January 2006 15 November 2006 25 December 2006 31 December 2006 7 January 2007 Steven Nelson Stephen Konarik WFO Peachtree City 5 January 2007 26 February 2008 15 December 2007 17 February 2008

  2. Outline • Brief Review of Severe Convection • Climatology of Cold Season Tornadoes • Case Studies • Summary / Forecasting Guidelines

  3. Review • Ingredients for Deep Moist Convection: (note, most of the time, DMC = thunderstorms) • Instability + Moisture + Lift (to the LFC) • Ingredients for Severe DMC: • All the above plus… • Greater instability and/or vertical wind shear • Warm Season: High Cape / Low Shear • Cool Season: Low Cape / High Shear

  4. Instability and Shear (1993) Low instability does not mean little or no chance of tornadoes ! Note the absence of F2+ tornadoes when minimum shear criteria is not met.

  5. Cool Season Tornado Climatology • Not studied much until recently • Used SvrPlot to study Georgia area significant cool season tornadoes • More thorough studies by Wasula et al. (2004) and Guyer et al. (2006) • Tornadoes produce majority of severe weather damage and loss of life in cool season. • Flooding and lightning much lower threat.

  6. Cool Season Tornado Climatology • Wasula et al. found approximately 50% of all southeast U.S. F2+ tornadoes occur in the cool season (Nov 1 – Feb 28) 1950-2001

  7. Cool Season Tornado Climatology • Guyer et al. found tornadoes much more likely to persist overnight in the cool season Southeast U.S. Tornadoes by Hour (All year) Southeast U.S. Tornadoes by Hour (Oct 15 – Feb 15, 1985-2004)

  8. Cool Season Tornado Climatology • Instability important but much lower values needed for F2+ tornadoes in the cool season MLCAPE for SE cool season F2+ tornadoes MLCAPE for all F2+ tornadoes

  9. Cool Season Tornado Climatology • Somewhat more shear needed for F2+ tornadoes in the cool season SRH for SE cool season F2+ tornadoes 0-3km SRH for all F2+ tornadoes 0-1km SRH for all F2+ tornadoes

  10. Historical Cool Season Tornadoesin the Southeast

  11. Case Studies 13 February 2000 – Camilla, GA F3 • Early morning (12am) • 19 deaths, 202 inj • CAPE ~ 800 J/kg • 0-3km SRH ~ 400 m2/s2

  12. Case Studies 11 November 2002 – Veterans Day Outbreak (F2) • Early morning (2am) • SPC High Risk • 25 deaths, 188 inj • Van Wert, OH F4 • CAPE ~ 2500 J/kg • 0-3km SRH ~ 350 m2/s2

  13. Recent Cool Season Tornadoes in Georgia

  14. Recent Examples 25 December 2006 – The “Santa Claus” Tornado • CAPE ~300 J/kg • 0-3km SRH ~ 600 m2/s2 • No watch or outlook • No CG lightning with storm! • Ben Hill F1 at 630 am EST, F0 tornado near Kibbee ~ 700 am.

  15. Recent Examples 15 December 2007 – Wilcox, Dodge, Treutlen EF2 • CAPE ~ 300 J/kg • 0-1 km SRH ~ 300 m2/s2 • Surface Td > 70 F • Supercell moved NE along strong warm front

  16. Recent Examples 26 February 2008 – Carroll EF3 11Z MLCAPE • Very low CAPE ~ 150 J/kg? • 0-1km SRH ~ 350 m2/s2 • Early morning event (6am) • 2 injuries, no fatalities • QLCS tornado 11Z MUCAPE 11Z 0-1km SRH

  17. Summary • “Ingredients” for cool season tornadoes the same as with all tornadoes: lift, moisture, instability and vertical wind shear. • 50% of F2+ tornadoes in the southeast occur between November and February. • Cool season tornadoes more likely to occur overnight. • Tornado-producing storms in low CAPE environments will produce very little or no lightning. • 25 Dec 2006 “Santa Claus” Tornado • Strong large-scale “dynamics” observed in several cases, but not necessary for significant cool season tornadoes.

  18. Guidelines • For F2+ tornadoes in the cool season, • Some instability is necessary (usually CAPE > 500 J/kg), but large values not needed if sufficient shear is present • Likewise, shear is necessary (0-1km SRH > 125 m2/s2), but large values not needed if relatively strong instability is present • Example guidelines for cool-season F2+ tornadoes based on research and case studies: • CAPE > 1500 J/kg and 0-1km SRH > 125 m2/s2 • CAPE > 500 J/kg and 0-1km SRH > 200 m2/s2 • CAPE > 150 J/kg and 0-1km SRH > 300 m2/s2 ??

  19. BONUS!! What kind of warning would you issue? • Slight risk to your west • No watch • 00Z sounding not yet in • ASOS observation just to the east of storm: • KXXX 150048Z 04004KT 1 3/4SM BR FEW090 14/13 (57/55 F) A2971 • 10 minutes after this time, tornado touches down ½ mile west of downtown! • Anemometer on roof of CNN center records 126 mph gust before it was destroyed.

  20. Questions? Steven.Nelson@noaa.gov Stephen.Konarik@noaa.gov

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