FORECASTING PARAMETERS

Lifted Index Marginal
0 to -3
Moderate
-3 to -6
Very Unstable
-6 to -9
Extreme
< -9
CAPE Weak
< 1000 J/kg
Moderate
1000 to 2500 J/kg
Very Unstable
2500 to 3500 J/kg
Extreme
> 3500 J/kg
LFC Height < 2,000 meters tornadoes more likely with supercells.
< 3,000 meters thunderstorms are more easily initiated.
Surface to 1 km Shear > 15 to 20 knots Favors supercell thunderstorms.
Surface to 6 km Shear 35 to 40 knots associated with supercell thunderstorms.
Effective Bulk Shear 25 to 40 knots associated with supercell thunderstorms.
BRN Shear 35 to 40 knots associated with supercell thunderstorms.
0 to 1km SR Helicity > 100 suggests increased threat of tornadoes with supercells
0 to 3 SR Helicity > 250 suggests increased threat of tornadoes with supercells
Storm-relative Helicity Supercell Threshold
150
Weak Tornadoes
150 to 299
Strong Tornadoes
300 to 449
Violent Tornadoes
> 450
Surface to 2 km SR Winds > 15 to 20 Favors sustained supercell thunderstorms.
4 to 6 km SR Winds > 15 Favors tornadic supercell thunderstorms.
9 to 11 km SR Winds HP Supercells
< 40
Classic Supercells
40 to 60
Low Precipitation
> 60
Significant Hail Parameter > 1.5 to 2.0 Favors hail greater than 2" in diameter.
Supercell Composite Marginal
1.2
Non-Tornadic
3.2
Weak Tornado
5.7
Sig. Tornado
10
Significant Tornado > 1 Associated with significant tornadoes.
Energy Helicity Index < 1 supercells & tornadoes unlikely
1 to 2 supercells and tornadoes possible
2 to 2.4 supercells likely and tornadoes possible
2.5 to 2.9 supercell tornadoes likely
3 to 3.9 strong tornadoes possible
> 4 violent tornadoes possible