How To Determine LI Value?

[Alex Torres]

The formula for determining the LI value is:

LI formula = Temperature of Environment at 500 mb - Parcel temperature at 500 mb

Simple, right? But, how do I get the temperature for both Environment and Parcel?

I've seen 500mb charts which can have a value of (top left) -14 and (bottom left) -20. I imaging that the -14 is the environment temperature? If this is correct, how do I find the Parcel temp?

Thank you. Best regards,
Alex

 

[rdale]

This should help. http://www.theweatherprediction.com/habyhints/300/

 

[Jeff Duda]

You have to lift the surface parcel. It requires either the use of a skew-T diagram or the use of complicated formulas. I wouldn't worry about trying to decipher LI - it's much too simple an index to have much value. CAPE and CIN provide more comprehensive information on parcel stability.

 

[Alex Torres]

This should help. http://www.theweatherprediction.com/habyhints/300/

Thanks. Very good and helpful site.

 

[Alex Torres]

You have to lift the surface parcel. It requires either the use of a skew-T diagram or the use of complicated formulas. I wouldn't worry about trying to decipher LI - it's much too simple an index to have much value. CAPE and CIN provide more comprehensive information on parcel stability.

I agree. By using the site posted above by rdale I was able to get the info I needed as well as learned more about using CAPE.

Thanks.

 

[JF Massicotte]

You have to lift the surface parcel. It requires either the use of a skew-T diagram or the use of complicated formulas. I wouldn't worry about trying to decipher LI - it's much too simple an index to have much value. CAPE and CIN provide more comprehensive information on parcel stability.

I would like to add, however, that LI gives a good indication about CAPE distribution ie fat CAPE vs slim CAPE profiles.

So for the same amount of CAPE, an environement with a larger LI will yield more robust updrafts. Another index used by SPC would be Normalized CAPE wich divides total amount de CAPE with the total depth of the positive area on the skew-T plot. One downfall of the LI that NCAPE doesn't have is that one would miss on a good profile if the largest part of the positive area is not at 500mb, NCAPE would then still catch it while LI wouln'd.

With today's tools, I prefer looking at a CAPE map and then judging the profile by lookig directly on a skew-T, numbers are numbers while a lot of things can be figured out on a plot.

 

[Alex Torres]

With today's tools, I prefer looking at a CAPE map and then judging the profile by lookig directly on a skew-T, numbers are numbers while a lot of things can be figured out on a plot.

Which site/s do you recommend for viewing and analyzing CAPE and skew-t diagrams?

Best regards,
Alex

 

[JF Massicotte]

Which site/s do you recommend for viewing and analyzing CAPE and skew-t diagrams?

Best regards,
Alex

For Skew-Ts I am very impressed with SHARPpy described on this thread by Greg Blumberg. It is a little bit complicated to install if you are not used to python but the little thing can do a lot in term of severe weather forecast.

For real time mesoanalysis I like the SPC meso site.

there are a lot of resources out there, but I like the Twisterdata click to view Skew-T/Hodo. Very convenient.

 

[Alex Torres]

For Skew-Ts I am very impressed with SHARPpy described on this thread by Greg Blumberg. It is a little bit complicated to install if you are not used to python but the little thing can do a lot in term of severe weather forecast.

For real time mesoanalysis I like the SPC meso site.

there are a lot of resources out there, but I like the Twisterdata click to view Skew-T/Hodo. Very convenient.

Thanks. SHARPpy is very impressive.

Best regards,
Alex