General thunderstorm (instability) indicators

Index Weak (low) Moderate Strong (high)
Surface based CAPE 300 to 1000 1000 to 2500 > 2500
Surface based Lifted-Index 0 to -2 -3 to -5 < -5
Convective Inhibition > 50 50 to 200 > 200
Total-totals > 42 > 48 > 50
K-Index 20 to 25 26 to 35 > 35
KO-Index   > 6 2 to 6 < 2
Showalter Stability Index > 2 =< 2  
Thompson Index 24 to 34 35 to 39 => 40
Jet stream      
Storm Relative Helicity 0-3 km 150-300(Possible supercell) 300-400(Supercells) 400+Tornadic possible
Thunderstorm Index      
       


K = K Index in °C
TT = total totals index in °C
PW = precipitable water for the entire sounding in cm
Temp = temperature on ground in °C
Dewp = dewpoint on ground in °C
θS = equivalent potential temperature in °K (= measure for instability)
LI = lifted index in °C
CAPE = convective available potential energy in J/kg
CIN = convective inhibition in J/kg
EH = environmental helicity in m²/s² 
SREH = storm relative environmental helicity in m²/s² 
StrmDir = storm direction in degrees
StrmSpd = storm speed in knots
EXAMPLE HODOGRAPH SKETCH #3
Strong speed shear and strong directional shear: supercell thunderstorm


SKETCH 3: ESE 24 knots  950 mb, S 43 knots  850 mb, SW 52 knots  700mb, WSW 77 knots  500 mb, W 95 knots  300 mb


EXAMPLE HODOGRAPH SKETCH #1
Weak speed shear and weak directional shear or weak speed shear and strong directional shear: single cell .




SKETCH 1:
SSE 10 knots  950 mb,
S 22 knots 850 mb,
SSW 23 knots  700mb,
SW 10 knots 500 mb,
S 13 knots  300 mb
EXAMPLE HODOGRAPH SKETCH #2
Strong speed shear and weak directional shear: multicell thunderstorm.
If deep layer speed shear (sfc-6km is >35 knots): risk for supercell thunderstorm which might split in a twin pair if directional shear is straight.  



SKETCH 2:
SE 19 knots  950 mb,
SE 35 knots  850 mb,
SSE 45 knots  700mb,
S 70 knots  500 mb,
SSW 85 knots  300 mb