Detailed description and key for examples:

Here is a sample skewT-logp excerpt, and parameter assessment box:                                                                                

Rather than "thresholds", the values and category strengths ("poor","marginal","ok","strong") used in examples should be viewed only as general guidelines and as a way of showing parameter strengths relative to each other.  See operational low-level thermodynamic parameter guidelines for further discussion.

For this example, even though shear-CAPE combinations, vertical shear, and LCL height are "strong" in value and appear quite favorable, the large CIN (> 200 J/kg) indicates a prohibitively deep stable low-level layer.  Storms in this environment will probably be elevated, and as a result, significant tornadoes are unlikely.  Because of these limiting factors (in dark blue), the parameter assessment box is colored light blue (instead of red or yellow) to indicate there is little or no potential for supercell tornadoes  (refer to the color coding listed further below).  A long-lived supercell developed in this environment, but was not tornadic.   The lack of a well-defined surface boundary to enhance low-level shear and thermodynamic factors may have also played a role (not shown).  Additionally, if the storm had moved into an environment with less CIN and lower LFC heights, one would need to be aware of this and the possibility of increased potential for tornadoes.

What follows is a more detailed description of profiles and parameter assessments used in all examples.

Examples are from RUC-2 model analysis or short-term forecast profiles associated with real supercell events.  While these are not actual sounding observations, such profiles are influenced by real observations and have been shown by Edwards and Thompson at SPC to be useful in estimating general environments near supercells events.   Model-derived profiles close to supercells in real time are also much easier to obtain.  Eta model analysis profiles were used in a few cases where RUC-2 profiles were not available.  As in Edwards and Thompson's work, each case uses actual surface observations within 20 to 50 miles of a supercell event in the inflow air mass to increase representativeness in the boundary layer, which is where model profiles are most often in error.   Thermodynamic parameters are computed using the most unstable parcel in the bottom 50-100 mb (surface or near-surface).

On the skewT-logp diagrams, CAPE is shown in red and CIN is shown in blue.  On each profile, pay attention to the areas of CIN and CAPE below 3 km (heavy dashed line), comparing these to the computed values to get a feel visually for what is "large" and "small".  On the sample skewT-logp diagram above, CIN is quite large (> 200 J/kg) and 0-3 km CAPE is small (< 30 J/kg), with a resulting LFC that is rather high (> 2500 m). 

Several environment parameters that appear important to supercells and supercell tornadoes are summarized in each of the examples.  To avoid over-focus on any single parameter, the assessment box shows several parameters evaluated together, beginning with important shear-CAPE factors:  

0-1 km EHI (Energy-helicity index):  This parameter developed by Hart and Korotky (based on data from Johns and Davies), incorporates low-level storm-relative helicity (SRH, the 0-1 km layer is considered most relevant from recent work by Rasmussen and Markowski) and total CAPE as a way of estimating potential for updraft tilting of streamwise horizontal vorticity and storm rotation in low-levels.  The computation is:   (CAPE x SRH)/160000    where the estimated total CAPE and SRH are shown in the upper left hand corner of the box.  Regarding support for significant supercell tornadoes, based on recent experience using the 0-1 km layer instead of 0-3 km, values below 1.0 are considered "poor"; 1.0 to 1.9 are "marginal"; 2.0 to 2.9 are "ok"; and values of 3.0 and above are "strong". 
BL-6 km shear is the straight vector difference between the mean lowest 500 m (boundary layer) wind and the wind at 6 km above ground.  This deep layer shear is important for organizing, supporting, and intensifying supercell updrafts, based on past work by Weisman and Klemp.  Here, shear values below 30 kts are considered "poor"; 30-37 kts are "marginal"; 38-45 kts are "ok"; and values above 45 kts and above are "strong".
LCL height is an indicator of relative humidity in low-levels from work by Rasmussen.  Low LCLs suggest large low-level humidity and less potential for evaporation and low-level cold pooling, while higher LCLs suggest more potential for cold outflow and an increasing low-level stable layer that is less favorable for near-ground mesocyclone intensification.  Here, values below 1000 m are considered "strong"; 1000-1249 m are "ok"; 1250-1499 are "marginal"; and values of 1500 m and higher are "poor".  It should be noted that in the high plains west of 99 deg W longitude, warm season supercells sometimes are able to produce tornadoes in environments with "marginal" or even "poor" LCL heights when other parameters are favorable.

Other low-level thermodynamic parameters are grouped near the bottom of the box  (see also operational low-level thermodynamic parameter guidelines).  In particular, relatively small CIN values and lower LFC heights are preferred as support for significant supercell tornadoes when shear-CAPE and deep layer shear are adequate:
  
CIN suggests the degree or strength of any low-level stable layer that is present.  Values of 150 J/kg and larger are considered "poor", suggesting an environment too "elevated" to support significant tornadoes; 100-149 J/kg are "marginal"; 50-99 J/kg are "ok"; values less than 50 J/kg are "strong".  Remember that in the central plains "marginal" to "ok" CIN values can support significant tornadoes if shear-CAPE combinations and deep shear are "strong".  (See operational low-level thermodynamic parameter guidelines.) 
LFC height also suggests the depth of any low-level stable layer that is present.  Heights of  2500 m and greater are considered "poor", suggesting an elevated environment unfavorable for significant tornadoes; 2000-2499 m are "marginal"; 1500-1999 m are "ok"; values less than 1500 m are considered "strong".  Similar to CIN, remember that in the central plains "marginal" to "ok" LFC heights can support significant tornadoes if shear-CAPE combinations and deep shear are "strong".  (See operational low-level thermodynamic parameter guidelines.)  
0-3 km CAPE:  Most significant tornadoes have at least some low-level CAPE, if CIN and LFC heights aren't too large.  Here, values less than 30 J/kg are considered "poor"; 30-59 J/kg are "marginal"; 60-89 J/kg are "ok"; and values of 90 J/kg and larger are "strong".  Smaller values of low-level CAPE are very sensitive to boundary-layer data and should not be trusted without reference to CIN and LFC height. CIN and LFC heights should be given more emphasis in assessing presence or absence of low-level stable layers than low-level CAPE alone.

Here is a summary of relative parameter values discussed above:

Again, rather than "thresholds" or "cutoffs", the values and category strengths ("poor","marginal","ok","strong") are somewhat arbitrary, and should be viewed only as general guidelines in showing parameter strengths relative to each other.

Parameter assessment boxes are classified and color coded according to suggested potential as follows:       

An exception to the above is if 0-3 km CAPE is unusually large (e.g., > 200 J/kg) and well-defined pre-existing boundaries are present with at least 20-30 kts of deep layer shear;  in such cases at least marginal potential for supercell tornadoes is suggested (yellow box).   Note again that when CIN is prohibitively large (e.g., > 150-200 J/kg) and LFC height is very high (> 2500), the strong low-level stability suggests little or no potential for supercell tornadoes (blue box, as above), even if vertical shear and shear-CAPE combinations are large. 

The type of supercell event that actually occurred in the example environment (tornadic with F-scale, or nontornadic) is indicated above the box.

In the sample parameter assessment box at the top of the page, CIN is prohibitively large ("poor", > 150 J/kg) and LFC heights are high (> 2500), indicating a deep stable layer below 3 km.   These factors suggest that, even with large SRH and "strong" vertical shear and shear-CAPE combinations, storms developing in this environment will be elevated, and that there is little or no potential for significant supercell tornadoes. 

Important Note:  Parameters can only hint at processes that are poorly understood and that interact in ways that are unclear, so the parameter assessments here should not be taken too strictly or too literally!  Also, in the examples we're lacking synoptic and mesoscale information (e.g., upper level features, mode of forcing, low-level boundaries, etc.) that is important in assessing severe weather potential.  With space limitations, our focus here is on factors from the general "environment" that suggest support for tornadoes.

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