© Craig Setzer and Al Pietrycha Supercell (mesocyclone) tornadoes: Supercell tornado environments Developed by Jon Davies – Private Meteorologist – Wichita,

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Presentation transcript:

© Craig Setzer and Al Pietrycha Supercell (mesocyclone) tornadoes: Supercell tornado environments Developed by Jon Davies – Private Meteorologist – Wichita, Kansas

Basic environment ingredients for supercell tornadoes Instability (CAPE) Enhanced horizontal vorticity near ground (SRH) (0-1 km) Deep-layer shear (0-6 km shear) Relatively low cloud bases? (low LCL heights) Basic environment ingredients for supercell tornadoes: (from accepted research over the last 15 years)

 Instability (CAPE)  Enhanced horizontal vorticity near ground (SRH) (0-1 km)  Deep-layer shear (0-6 km shear)  Relatively low cloud bases? (low LCL heights)  Sizable 0-3 km CAPE (relatively low LFC heights)? Basic environment ingredients for supercell tornadoes: Basic environment ingredients for supercell tornadoes: (Davies 2003)

Instability (CAPE) Enhanced horizontal vorticity near ground (SRH) (0-1 km) Deep-layer shear (0-6 km shear) Relatively low cloud bases? (low LCL heights) Basic environment ingredients for supercell tornadoes: Basic environment ingredients for supercell tornadoes:

Need CAPE to generate an updraft for vertical stretching

ground 1 km 3 km Need low-level shear to generate horizontal vorticity (“spin”)

Tilting and stretching of horizontal vorticity: Low-level mesocyclones, possible tornadoes? Combinations of CAPE and low-level shear

EHI = 2.0 EHI = CAPE x SRH from Johns, Davies, & Leftwich 1993 Energy-Helicity Index F2+ tornadic storms

EHI = 2.0 EHI = CAPE x SRH from Johns, Davies, & Leftwich 1993 Energy-Helicity Index F2+ tornadic storms Problems with EHI in this area of chart when SRH is large and CAPE is small

Rasmussen (2003) 0-1 km EHI

Small CAPE – large SRH (many cool season cases) Cold core tornado situations (500 mb closed lows) Nonsupercell/nonmesocyclone tornadoes CAPE-SRH combinations often don ’ t work well in these situations: CAPE-SRH combinations often don ’ t work well in these situations:

Instability (CAPE) Enhanced horizontal vorticity near ground (SRH) Deep-layer shear (0-6 km shear) Relatively low cloud bases? (low LCL heights) Basic environment ingredients for supercell tornadoes: Basic environment ingredients for supercell tornadoes:

Deep shear helps organize storms and strengthen updrafts This is important for most supercell tornadoes

30 kts 40 kts 50 kts from Davies and Johns 1993 F2+ tornadic storms

Instability (CAPE) Enhanced horizontal vorticity near ground (SRH) Deep-layer shear (0-6 km shear) Relatively low cloud bases? (low LCL heights) Basic environment ingredients for supercell tornadoes: Basic environment ingredients for supercell tornadoes:

clear slot/downdraft ( R F D ) updraft inflow low cloud bases & large humidity reduce cold pooling? downdraft not cold - contains buoyancy (Markowski et al. 2002) Low cloud bases (low LCL heights):

1500 From Craven and Brooks 2005

Other environment characteristics that may have some relevance to tornadoes: Other environment characteristics that may have some relevance to tornadoes: Relatively low LFC heights? Sizable CAPE in low-levels (below 3 km)? (less work for low-level parcels of air to move upward and “stretch” in updrafts?)

F1 - F4 tornadoes by MLLFC range (from 518 supercell cases using RUC profiles) (Davies 2003)

large CIN high LFC no CAPE 0-3 low LCL small CIN low LFC large CAPE 0-3 low LCL Contrasting environments This setting would probably be more favorable for tornadoes:

 Instability (CAPE) Enhanced horizontal vorticity near ground (SRH) Deep-layer shear (0-6 km shear) Relatively low cloud bases? (low LCL heights) Sizable 0-3 km CAPE (relatively low LFC heights)? Basic environment ingredients for supercell tornadoes: Basic environment ingredients for supercell tornadoes:

Instability (CAPE) Enhanced horizontal vorticity near ground (SRH) Deep-layer shear (0-6 km shear) Relatively low cloud bases? (low LCL heights) Sizable 0-3 km CAPE (relatively low LFC heights)? Basic environment ingredients for supercell tornadoes: Basic environment ingredients for supercell tornadoes: STPSTP EHI

0-1 km MLEHI or more? MLCAPE J kg -1 or more?* 0-1 km SRH m 2 s -2 or more?* 0-6 km shear kts or more? * MLLCL heights below m? * 0-3 km MLCAPE J kg -1 or more, MLLFC less than m? Environment parameter values suggesting notable support for supercell tornadoes? * in SPC ’ s STP parameter Be careful using in small CAPE - large SRH settings!

Significant Tornado Parameter (updated - Thompson 2005): Significant Tornado Parameter (updated - Thompson 2005): STP = MLCAPE/1500 x SRH 0-1 /150 x shear 0-6 /40 x (2000-LCL)/1500 x (200+CIN)/150 set to 0 if shear 0-6 < 25 kts set to 1 if LCL < 1000 m set to 1 if CIN < -50 J/kg set to 1.5 if shear 0-6 > 60 kts MLCAPE in J/kg; SRH in m 2 /s 2 ; shear in kts; LCL in m; use lowest 100 mb mixed-layer lifted parcels

(Surface boundaries can enhance and focus these parameters) Use with caution… the atmosphere doesn’t recognize thresholds!!! Environment parameters suggesting support for supercell tornadoes? 0-3 km CAPE < 20 J/kg J/kg J/kg 60+ J/kg Be careful using in small CAPE - large SRH settings! 0-6 km shear < 30 kts kts kts 45+ kts

 Look for areas of focus and convergence where storm development might be expected, and then assess how the parameter fields may affect that area. Fit the parameter fields with the surface pattern ! Don’t treat them as “magic numbers” or “bulls eyes” ! When using forecast fields of these ingredients: When using forecast fields of these ingredients:

9 June 2005 Graham County KS tornado (w/Tim Samaras) 8 May 2005 – central Kansas: nonsupercell/nonmesocyclone tornado 9 June 2005 – northwest Kansas: Strong supercell tornadoes (probe deployment attempt w/Tim Samaras)

June 9, 2005

Storm relative helicity (SRH)

Energy-helicity index (EHI)

0-6 km shear

LCL height

LFC height

0-3 km CAPE (low-level instability)

MLCAPE 3780 J/kg 0-1 km SRH 140 m 2 /s km EHI km shear 41 kts MLLCL 1290 m MLLFC 1610 m CAPE 0-3 km 90 J/kg STP 2.4

Significant Tornado Parameter (STP) All the basic environment ingredients that suggest support for supercell tornadoes came together in this area.

1 st tornadic storm develops

Tornado southwest of Hill City, KS ~ 4:25 pm CDT