Lifted Index
Measure of instability. Numbers -4 or lower indicate the likelihood of severe storms.

Lifted Index

Theta-E
Another instability tool. Ridges indicate unstable air.

K-Index
Indicator of the probability of thunderstorms. 20-24= 20-40% chance, 25-29= 40-60% chance, 30-35= 60-80% chance, and 35+ indicates a >80% chance of thunderstorms

K-Index

Showalter Index
A good indicator of Air Mass thunderstorms. Derived from the Skew-T upper air soundings. Values -2 and below indicate possible severe t-storms.

Total Totals Index
44-48= Scattered moderate t-storms,49-54= Scattered heavy t-storms, 55+ indicate severe storms.

Total Totals Index

SWEAT Index
Values of 300 or greater imply severe thunderstorm potential. Values of 400 or greater imply tornado potential. Values rarely reach a level of 800.

Convective Available Potential Energy (CAPE)
< 300 Very weak convection, 300-1000 Weak, 1000-2500 Moderate, 2500-3000 Strong, 3000+ Wizard of Oz

Convective Available Potential Energy (CAPE)

Helicity Contour
This is a contour plot of helicity which is the amount of storm relative rotation/shear in the atmosphere. A value of 400-500 is often needed to produce severe storms.

Cross Totals Index
<= 17 Thunderstorms unlikely, 18-19 Isolated thunderstorms, 20-21 Scattered thunderstorms, 22-23 Scattered thunderstorms/ isolated severe, 24-25 Scattered thunderstorms/ few severe/isolated tornadoes, 26-29 Scattered to numerous t-storms/few severe/few tornadoes, >= 30 Numerous t-storms/scattered severe/scattered tornadoes.

Vertical Total Totals Index
< 25 Thunderstorms unlikely, 25-26 Scattered thunderstorms, 27-30 Scattered t-storms/few severe/isolated tornadoes, 31-32 Scattered-numerous t-storms/few tornadoes, 33-34 Numerous thunderstorms/ few tornadoes, > 34 Numerous t-storms/ scattered severe/scattered tornadoes.

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