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Cape value

This post was from a previous version of the WRF&MPAS-A Support Forum. New replies have been disabled and if you have follow up questions related to this post, then please start a new thread from the forum home page.


I'm looking for cape information in order to predict storm conditions. Then i calculate cape from wrfout file with ncl function wrf_user_getvar(a,"cape_2d",-1). It works but the value seems not accurate, with storm conditions i should have between 700 and 5000 J/KG, however i get no more than 400 J/KG. Does someone has any idea about this strange value, is unit correct, is it possible to calculate easily cape from other variables to verify the value given with ncl function?
Thanks in advance for your answers
I first would like to apologize for the long delay in response. I've been traveling for a few weeks and am just now catching up with forum inquiries. Thank you for your patience.

You could try looking at the code NCL uses for CAPE to see if the calculations are what you would expect, and to ensure you're calculating at the correct location. You could also try another post-processing program, like RIP, to see if you get similar results. My guess is you would, though. Model simulations are not perfect and there can be discrepancies between the output and observations. You should look at other variables to make sure they look correct, as well, and if not, perhaps modify some of your WRF run-time settings - such as physics settings.
No problem my question didn't need a quick answer. First of all i tried to look for value given by "official" weather forecast to compare with ncl calculation, but i didn't find comparable characteristics. I tried with AFWA diagnostics but the results are worst.
Therefore i decided to store the ncl calculations as it is and to compare with the observations on a long period (summer time) and try to get something as a thumb rule.
Nevertheless i have an another question about the CIN value: the CIN values given by ncl are always positive while with AFWA it's always negative, i thought it must be negative, what is the reality?
Hi Jef,
As these questions are more specifically related to NCL, I would like to ask you to post in the NCL section of this forum. There is a different set of experts who can answer those questions, and they are more equipped than our group.