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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
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