Extended Abstract (216K)P12.5
On low-level Thermodynamic parameters associated with tornadic and nontornadic supercells
Jonathan M. Davies, Private Meteorologist, Wichita, KS
Recent numerical modeling by some researchers has shown that enhanced CAPE in low-levels can dramatically increase storm updraft intensity. Related more specifically to tornado environments, a couple studies using observed and model soundings have found that CIN tends to be less in thermodynamic profiles associated with supercell tornadoes. Moreover, direct mobile mesonet observations in the field have shown that rear flank downdraft parcels entering tornadic circulations have less surface-based CIN and more surface-based CAPE.
From the above research, it appears that low-level thermodynamic factors are important regarding potential for supercell tornadoes. But apart from surface dewpoint depression (related to height of LCL), little attention has been given to other low-level thermodynamic factors and parameters on observable or estimated operational scales in severe weather forecasting.
In this investigation, several low-level buoyancy parameters (CIN, CAPE below 3 km AGL, LFC height) from more than 300 supercell cases during 1999 through 2001 are examined using RUC-2 analysis and short-term forecast soundings. RUC-2 profiles are widely available and have been shown by operational researchers to be a helpful tool for estimating and evaluating environments near supercells when observed soundings are not available. This is particularly true when such profiles are updated and modified by actual observations such as hourly surface data, as done in this study.
Results from this investigation show some detectable differences between tornadic and nontornadic cases. It will be shown that parameters such as near-surface CIN, CAPE below 3 km, and LFC height can contribute useful short-term information in many cases when attempting to diagnose environments with increased likelihood for supercell tornadoes. It is important that such information be combined with assessment of established supercell and tornado parameters incorporating low-level and deep-layer wind shear.
Some general guidelines will be suggested from the investigation results, supported by some case examples.
Supplementary URL: http://members.cox.net/jdavies1/
Poster Session 12, Tornado and Severe Storm Environments
Thursday, 15 August 2002, 3:00 PM-4:30 PM
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