SkyStef's weather page
SSI > 2: no thunderstorms.
(*) To find 500 hPa parcel temperature: construct LCL for parcel at 850 hPa. From this point ascend saturated adiabatically to the 500 hPa level and read off.
This Index doesn't work well if a frontal surface or inversion is present between 850 hPa and 500 hPa.
Formula used: SSI = T - Tparcel (both T at 500 hPa)
Note: Java script must be enabled