© craig setzer and al pietrycha supercell (mesocyclone) tornadoes: supercell tornado environments...

© 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




Sizable 0-3 km CAPE (relatively low LFC heights)?



(Davies 2003)

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:


vorticity near ground (SRH)





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

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:





Sizable 0-3 km CAPE (relatively low LFC heights)?



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)?



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


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/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)


All the basicenvironmentingredients thatsuggest supportfor supercelltornadoes came together in this area.

1st tornadic stormdevelops

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

© craig setzer and al pietrycha supercell (mesocyclone) tornadoes: supercell tornado environments...

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