CAPE and Helicity




The following indices should be used to evaluate thunderstorm development, severity and potential tornadic activity in the NASP area:
Convective Available Potential Energy (CAPE)

< 0 =Stable 

0 1000 =Marginally unstable 
1000 2500 =Moderately unstable 
2500 3500 =Very unstable 
3500 4000 =Extremely unstable 

Storm Relative Environmental Helicity (SREH)

150 =The approximate threshold for supercell development 

150 299 = Weak Tornadoes (F0 and F1) possible 
300 - 449 =Strong tornadoes (F2 and F3) possible 
>450 =Violent tornadoes (F4 and F5) possible 

Lifted Index (LI)

-3 or less = unstable to very unstable, strong thunderstorm potential 

Showalter Index (SI

3 - 1 = Thunderstorm possible, strong trigger needed 

0 (-3) = Unstable, Thunderstorms probable 
-4 (-6) = Very Unstable, heavy thunderstorm potential 
< (6) =Extremely unstable, heavy to strong thunderstorm potential 

K Index(KI)

20 25 = Isolated thunderstorms 

26 30 = Widely scattered thunderstorms 
31 - 35= Scattered thunderstorms 
35 and > = Numerous thunderstorms 

Total Totals (TT)

48 =Scattered thunderstorms, isolated severe thunderstorms 

50 =Scattered thunderstorms, few severe thunderstorms, isolated tornadoes 
52 =Scattered to numerous thunderstorms, few to scattered severe thunderstorms, few tornadoes 
56 =Numerous thunderstorms
Concept Mapping Toolkit
Insitute for Human and Machine Cognition
The University of West Florida