Lifted Index
The Lifted Index (LI) is defined as a rising parcel's temperature when it reaches
the 500 millibars level (at about 5,500m or 18,000 feet asl), subtracted from
the actual temperature of the environmental air at 500 mbar. If the Lifted
Index is a large negative number, then the parcel will be much warmer than its
surroundings, and will continue to rise. Thunderstorms are fueled by strong rising air, thus the
Lifted Index is a good measurement of the atmosphere's potential to produce
severe thunderstorms.
The Lifted Index (LI) |
RANGE IN K |
COLOR |
AMOUNT OF INSTABILITY |
THUNDERSTORM PROBABILITY |
more than 11 |
BLUE |
Extremely stable conditions |
Thunderstorms unlikely |
8 to 11 |
LIGHT BLUE |
Very stable conditions |
Thunderstorms unlikely |
4 to 7 |
GREEN |
Stable conditions |
Thunderstorms unlikely |
0 to 3 |
LIGHT GREEN |
Mostly stable conditions |
Thunderstorm unlikely |
-3 to -1 |
YELLOW |
Slightly unstable |
Thunderstorms possible |
-5 to -4 |
ORANGE |
Unstable |
Thunderstorms probable |
-7 to -6 |
RED |
Highly unstable |
Severe thunderstorms possible |
less than -7 |
VIOLET |
Extremely unstable |
Violent thunderstorms, tornadoes possible |