© 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 ingredientsfor 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 ingredientsfor supercell tornadoes:
Basic environment ingredientsfor 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 ingredientsfor supercell tornadoes:
Basic environment ingredientsfor supercell tornadoes:
Need CAPE to generate an updraft for vertical stretching
ground1 km3 km
Need low-level shear to generate horizontal vorticity (“spin”)
Tilting and stretching of horizontal vorticity:
Low-level mesocyclones, possible tornadoes?
Combinations ofCAPE and
low-level shear
EHI = 2.0
EHI = CAPE x SRH 160000
from Johns, Davies, & Leftwich 1993
Energy-Helicity Index
F2+ tornadic storms
EHI = 2.0
EHI = CAPE x SRH 160000
from Johns, Davies, & Leftwich 1993
Energy-Helicity Index
F2+ tornadic storms
Problems
with EHIin this area
of chartwhen SRH islarge 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 ingredientsfor supercell tornadoes:
Basic environment ingredientsfor 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 ingredientsfor supercell tornadoes:
Basic environment ingredientsfor 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 airto move upward and “stretch” in updrafts?)
F1 - F4 tornadoes by MLLFC range
(from 518 supercell cases using RUC
profiles)(Davies 2003)
large CINhigh LFCno CAPE0-
3
low LCL
small CINlow LFClarge CAPE0-3
low LCL
Contrastingenvironments
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 ingredientsfor supercell tornadoes:
Basic environment ingredientsfor 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 ingredientsfor supercell tornadoes:
Basic environment ingredientsfor supercell tornadoes:
STP
EHI
0-1 km MLEHI 2.0-3.0 or more? MLCAPE 500-1000 J kg-1 or more?*
0-1 km SRH 150-200 m2s-2 or more?* 0-6 km shear 30-35 kts or more?*
MLLCL heights below 1200-1500 m?*
0-3 km MLCAPE 40-60 J kg-1 or more, MLLFC less than 2000-2500 m?
Environment parameter values suggesting notable support for
supercell tornadoes?
Environment parameter values suggesting notable support for
supercell tornadoes?
*in SPC’s STP parameter
Be carefulusing in
small CAPE -large SRHsettings!
Significant Tornado Parameter(updated - Thompson 2005):
Significant Tornado Parameter(updated - Thompson 2005):
STP = MLCAPE/1500 x SRH0-1/150
x shear0-6/40 x (2000-LCL)/1500 x (200+CIN)/150
set to 0 if shear0-6 < 25 kts
set to 1 if LCL < 1000 m
set to 1 if CIN < -50 J/kg
set to 1.5 if shear0-6 > 60 kts
MLCAPE in J/kg; SRH in m2/s2; 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 20-39 J/kg 40-59 J/kg 60+ J/kg
Be carefulusing in
small CAPE -large SRHsettings!
0-6 km shear < 30 kts 30 - 35 kts 36 - 44 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
http://www.spc.noaa.gov
http://www.spc.noaa.gov
Storm relative helicity (SRH)
http://www.spc.noaa.gov
Energy-helicity index(EHI)
0-6 km shear
http://www.spc.noaa.gov
LCL height
http://www.spc.noaa.gov
LFC height
http://www.spc.noaa.gov
0-3 km CAPE(low-level instability)
http://www.spc.noaa.gov
MLCAPE 3780 J/kg0-1 km SRH 140 m2/s2
0-1 km EHI 3.20-6 km shear 41 ktsMLLCL 1290 mMLLFC 1610 mCAPE 0-3 km 90 J/kgSTP 2.4
Significant Tornado Parameter(STP)
http://www.spc.noaa.gov
All the basicenvironmentingredients thatsuggest supportfor supercelltornadoes came together in this area.
1st tornadic stormdevelops
Tornado southwest of Hill City, KS ~ 4:25 pm CDT