About relatively large CIN values associated with some significant tornado cases

Operationally, CIN values greater than around 50 J/kg are often viewed as "large" or "significant" and not very favorable for initiation of surface-based non-elevated severe convection.  But from investigations using RUC-2 profiles, there are times when significant tornadoes can occur with CIN considerably larger than 50 J/kg when using the most unstable parcel in the bottom 50 or 100 mb.  In a few signficant tornado cases, surface-based CIN has been estimated as large as near 150 J/kg.

A logical question is:  How can storms that support tornadoes initiate and evolve in such "large CIN" environments?

The figure below shows a RUC-2 forecast profile (updated by an actual surface observation) associated with an F4 tornado just northwest of Lincoln, Nebraska on 6/13/01.   This profile suggests how surface-based convection capable of supporting tornadoes might initiate and continue when there is significant surface or near-surface CIN.

In this example, it is quite possible that convection initiated through lifting of elevated parcels from around the 800 mb level (see dotted lifted parcel path), where there is only 22 J/kg of CIN to overcome (small unshaded area bounded by heavy line).  Then, as the updraft became stronger and more established, the convection probably became more surface-based, pulling parcels through a fairly large area of surface-based CIN (blue shaded area).  Notice that, for a surface parcel, there is a notable amount of 0-3 km CAPE (> 70 J/kg) located just above the CIN layer.  This might have been a factor in helping to sustain surface-based or near surface-based convection, even with the significant CIN.  It is also important that total CAPE and vertical shear were large (not shown, CAPE 4000+ J/kg, 0-3 km SRH 200+ m2/s2, 0-1 km EHI 3.5, 0-6 km shear near 40 kts), all of which would have likely helped to generate a strong mesocyclone that could intensify through a moderately deep stable layer near the ground.  The observed Valley, Nebraska sounding 35 miles to the northeast (not shown) also indicated strong vertical shear, along with around 80 J/kg of CIN (not quite as strong as forecast). 

Cases like this suggest that environments with significant near-surface CIN "balanced" by a moderately low LFC and some 0-3 km CAPE just above the CIN layer can certainly support supercell convection and significant tornadoes, particularly if accompanied by strong total CAPE, SRH and deep shear.  Such environments are most common in the plains states during the warm season.  Below are two similar RUC-2 profile examples:. 
 
(RUC-2 analysis 00 UTC 4/15/01 at P28, using 23 UTC sfc ob)                  (RUC-2 3-hr fcst valid 20 UTC 6/11/01 at MVE, using 19 UTC sfc ob at AQP)

Notice how the blue (CIN) and red (CAPE) areas below 3 km tend to "balance" each other, and also notice the moderate to large SRH, vertical shear, and shear-CAPE combinations.  Both of these cases were associated with significant tornadoes: the first a large F2 tornado near Pratt, Kansas on 4/14/01, and the second a large F3 tornado that caused injuries and damage at Benson, Minnesota on 6/11/01. 

It should be noted that none of the 300+ RUC-2 supercell profiles investigated with surface CIN larger than around 150-160 J/kg were associated with significant tornadoes.  Just as important, no significant tornadoes were associated with surface or near-surface CIN that extended throughout the bottom 3 km, resulting in an LFC near or above 3000 m and an absence of  low-level CAPE*.  Such situations are significantly "elevated", with primary inflow probably coming from well above the boundary-layer and a deep low-level stable layer that appears to preclude the development of significant tornadoes.  Go to examples of strongly "elevated" supercell environments to see some examples.

*A cautionary note:  Be careful about checking surface observations in environments that appear to have large CIN and no 0-3 km CAPE... see discussion about importance of local surface observations in computing low-level CAPE and CIN.

Going back to the question of initiation of supercell storms that can produce significant tornadoes when relatively large surface or near-surface CIN is present, following are a couple of profile examples corresponding to the two cases immediately above, using the commercially-available RAOB software.  These show multiple parcel lifts that suggest how a storm might initiate from elevated lifted parcels if the profile is configured in such a way that elevated parcels can yield both positive buoyancy and small CIN.  Then, if an updraft persists and intensifies, the storm may become more surface-based as low-level parcels that are more unstable are worked into the updraft.  This is probably more likely to happen if the near-surface CIN layer is not too deep and there is also some 0-3 km CAPE above the CIN layer based on near-surface parcels.  Storm initiation is a complex and poorly understood issue, but relevant CIN regarding initial storm development can certainly vary depending on lifted parcel and layer.
4/14/01 RUC-2 profile near tornadic supercell in Pratt Co., Kansas    
6/11/01 RUC-2 profile near tornadic supercell in Swift Co., Minnesota

Regarding potential for tornadoes, the most relevant lifted parcels are probably the most unstable parcels in the bottom 50-100 mb ("near-surface").  As previously noted, if CIN with the most unstable near-surface parcel is notably more than 150J/kg, significant tornadoes are unlikely because of the depth or strength of the low-level stable layer, even with large SRH and vertical wind shear.

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