A Primer on Low-level Thermodynamic Parameters When Assessing Supercell Tornado Environments
                  (best viewed using 1024 x 768 pixels display)
by Jon Davies, Private Meteorologist, Wichita, KS    (revised 7/1/02)      jdavies1@cox.net                                    LLbuoyimage.gif (4171 bytes)

NEW 7/1/02 ===>2002 case studies combining EHI / deep shear / LCL / CIN / LFC to evaluate tornado potential with supercells in varying environments

UPDATED 5/1/02 ===>On Low-Level Thermodynamic Factors as an Aid to Situational Awareness about Tornadic Supercell Environments (includes several 2001 & 2002 case studies)
                                                                         (PowerPoint presentation for NWS Central Region offices April 2002 -- requires Internet Explorer)

The purpose of this page is to help document some work I've done regarding low-level thermodynamic parameters combined with shear-CAPE factors in tornadic and nontornadic environments.  Because these parameters seem to be useful in a number of situations,  I've put together this primer at the request of some SOO's and forecasters.  Lower LCL heights and  indicating increased boundary-layer humidity have been well documented regarding their association with supercell tornadoes from work by Rasmussen and Blanchard.  The work here moves on to look at near-surface CIN, LFC height, and low-level CAPE as additional and potentially helpful low-level thermodynamic parameters.  Such parameters may be particularly useful in diagnosing environments that are significantly "elevated" where supercells above a deep stable low-level layer are less likely to produce significant tornadoes.

I've written a preprint paper regarding some of this material for the San Antonio SLS conference in August 2002.  In this recent work, I've shifted the emphasis from low-level "buoyancy" (which possibly implies too much of a focus on low-level CAPE) to low-level thermodynamic parameters together (LCL, CIN, LFC, low-level CAPE).  CIN and LFC depictions are more widely available to forecasters than low-level CAPE/buoyancy, and experience is showing these to be more consistent than stand-alone depictions of low-level CAPE, which can be quite variable depending on method, lifted parcel, and forecast model used.

The material here gives some background and suggests some ways to incorporate CIN, LFC height, and low-level CAPE with LCL and shear-CAPE methods in operational assessment of short-term potential for tornadic supercells.  Some examples are provided, as well as a brief archive of cases that will be expanded as time permits.  Please remember that the environment examples here are only model-estimated "snapshots", and that analysis of other factors such as upper-level synoptic-scale features, mode of forcing, and low-level mesoscale boundaries is also very important.

===>A big thanks goes to Rich Thompson and Roger Edwards at SPC for allowing me to use a portion of their RUC-2 supercell profiles database, which provided some significant input to the first two sections below.  Thanks also goes to Pete Wolf, SOO at NWS Wichita, for helpful discussions and his suggestions in putting this together.
This information is not peer-reviewed, so please use with caution.  (Clicking on a thumbnail image will bring up a larger image.)