|SKEW-T: A LOOK AT EI (ENERGY INDEX)
METEOROLOGIST JEFF HABY
1. What is EI?
EI (Energy Index) is an index for assessing the
severe storm potential by comparing the heat and moisture
characteristics between the low level (850 mb) and middle level environment (500 mb). An environment
that is warm and moist in the low levels and cool and dry in the middle levels is
2. How is EI determined?
cp= specific heat for dry air at constant pressure (1,004 JK^-1kg^-1))
T= temperature at pressure level (found on sounding, units of K)
g= gravity (9.8 ms^-2)
Z= geopotential height (found on sounding, m)
L= latent heat of vaporization (~2,400,000 Jkg^-1)
w= mixing ratio (found on sounding, kg/kg)
The sounding at the bottom has an EI of -3.8 C
3. Operational significance of EI:
|EI > 0 ||No Activity Expected||-2 < EI < 0 ||Isolated Severe Thunderstorms Possible
||EI < -2 ||Severe Thunderstorms Probable, Tornadoes Possible
a. Cap must break for the EI value to have significance.