ARW-WRF Simulations of Thermodynamic Destabilization Supporting MCS Initiation in Differing Warm-Season Meteorological Regimes

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Monday, 5 November 2012: 5:00 PM
Symphony II (Loews Vanderbilt Hotel)
Stanley B. Trier, NCAR, Boulder, CO; and C. A. Davis, D. A. Ahijevych, and K. W. Manning

The initiation and sustenance of organized deep convection is a challenging problem in numerical weather prediction. The evolution of thermodynamic vertical structure is an important factor governing organized deep convection, including mesoscale convective systems (MCSs), which are often responsible for severe weather and flash floods. The current research aims to quantify how lower-tropospheric inhibition energy for deep convection (CIN) is overcome in convection-permitting versions of the Advanced Research Weather Research and Forecast (ARW-WRF) model. Though many physical processes involved in convection initiation (CI) have been proposed, there has been little direct quantitative evaluation of how various CI mechanisms eliminate or lessen CIN. To address this issue, diagnostic capability has been developed to examine how the maximum negative buoyancy (Bmin) beneath the level of free convection evolves for the most unstable air parcels (i.e., those with the largest equivalent potential temperature) in the path of incipient or mature simulated deep convection. Here, the quantity Bmin is used as a proxy for CIN because Bmin has the desirable property of being continuous and is also more amenable to budget calculations elucidating the causes of thermodynamic destabilization since it does not require vertical integration. Bmin and related model-based diagnostics will be presented for 0-24 forecasts from two different six-day retrospective periods of active convection occurring in different large-scale weather patterns. The first regime is characterized by translating cold fronts, which deep convection formed mostly along or southeast of (Fig. 1a). In the second regime, propagating deep convection occurs mostly along or north of quasi-stationary surface fronts (Fig. 1b).