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Energy/Helicity Index calculator

 

 

Enter ML100 CAPE* (J/kg)
Enter the SREH 0-3km (mē/sē)
The Energy/Helicity Index is

 

* ML100 CAPE = conservative estimate of CAPE, lifting an average parcel in the bottom 100 hPa of a sounding.

Maps of CAPE on the internet = surface-based CAPE (or SBCAPE) which starts in lowest 2 meter.

Convert SBCAPE to ML100 CAPE with estimation table below

SBCAPE ML100 CAPE Factor
10 0.4 0.04
20 0.9 0.05
50 3 0.07
100 9 0.09
200 23 0.12
500 83 0.17
1000 218 0.22
1500 383 0.26
2000 571 0.29
2500 778 0.31
3000 1002 0.33
4000 1495 0.37
5000 2039 0.41

 

EHI    0.00 to 0.34  (mean = 0.14) : ordinary cell
EHI    0.20 to 1.46  (mean = 0.64) : supercell (F0, F1 tornadoes)
EHI    0.42 to 2.87  (mean = 1.48) : supercell (= > F2 tornadoes)

 


Tests on the field (in the States) showed there is no good correlation between EHI values and severe weather events.

Formula used : (ML100 CAPE x SREH) / 160000
 

 

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