Lid Strength Index is to Lifted Index
as CINH is to CAPE
as 700 mb temps are to 500 temps
CINH is a more precise measure of the capping as CAPE is of the instability, while 700 mb and 500 mb temps seem like rather rough estimates of the capping/instability (these temps are dependent on time of year, location, and the T/Td's at the srurface).
However, I've found the LSI to be the best indicator of initiation potential and even whether or not your storms will be surface based. The LSI measures the "width" of the cap on a Skew-T. It seems storms have a much more difficult time with a fatter cap (wider inversion on the sounding), than they do with a skinnier one, even if the CINH is actually less on the sounding with a fatter cap. You've got less CINH overall, but it seems that fat cap is like a brick wall. Initial updrafts (the turkey towers that initially fail) might have an easier time modifying those temps profiles and eroding the capping if it's skinnier, priming the pump for your later supercells. It's also like how you get much more robust updrafts with short fat cape, than you do with tall skinny cape, even if the cape is actually greater on the tall skinny cape sounding.
My chase targeting lives or dies by the LSI and 3km CAPE plots. If I don't see < 1 LSI and some ~100 3km, I'm pretty sure I'm not seeing a tornado. it's the best discriminator I've found. These plots are very finicky though.
You can get storms when the LSIs are high (positive, +3 or more), but these storms are almost always elevated, usually because the boundary layer is cool, or the capping inversion is preventing your storm from getting surface based inflow.
As a general rule of thumb, greater than +3 LSI and you're not seeing a supercellular tornado. You'll need some significant forcing to see one when it's +1 to +3. A diverging trough bisecting a sharp boundary. Ideally you want to see that LSI < 1 if you want a good shot at a tornado, you want to see a large area with these values (not a tiny crack), and you want a window where these values exist for several hours. Landspouts, gustnadoes, and spinups are still possible with LSIs +5 or greater. So you'll see chasers reporting tornadoes on high plains storms and elevated supercells/MCSs (like we had Wednesday), but it's almost always the case that they're seeing one of these features.
The NAM seems to have the best handle on this parameter I've found. it's very finicky so you'll see changes even up to 24 or 12 hours before the event. The GFS appears to be sloppy, low res with this parameter and makes gauging initation timing and how large the hole in the cap is difficult. The RUC is often too bullish with its parameters and may not be a good discriminator.
The caveat is that this assumes the NAM is right. It seems many people are doubting it for 4/26's setup.
The other caveat is that this is based on my own amateur, anecdotal experience.
I browse this parameter using a frameset I created to make browsing's Earl's site easier:
http://skip.cc/chase/models/earlnamsvr.php
A previous explanation:
http://www.stormtrack.org/forum/sho...orm-initiation&p=260587&viewfull=1#post260587
