P3.1 Dynamics and Predictability of MCVs Estimated through High-Resolution Deterministic and Probabilistic (Ensemble) Forecasts

Tuesday, 5 October 2004
Dan Hawbliztel, Texas A&M University, College Station, TX; and F. Zhang, Z. Meng, and C. A. Davis

The focus of this study is to examine the dynamics and predictability of an MCV circulation and associated moist convection. While several studies have focused on analysis of the dynamics and thermodynamics of real and simulated vortices, few have addressed the ability to predict MCVs using numerical models. It has previously been proposed that convectively-induced latent heating has dramatic effects on midlevel potential vorticity which can lead to MCV development and intensification. In addition, several studies have concluded that shear and instability, both ambient and MCV-modified, are important to MCV strength and longevity as well as secondary convection. However, several factors regarding MCV intensification are still unclear, including the dynamic processes leading to mid-level rotation and especially for long-lived significant MCVs. Thus, evaluation of MCV dynamics and predictability through high-resolution observations and numerical modeling is currently a key issue to be addressed. One such MCV formed during the early morning hours of 11 June 2003 as an extensive stratiform region resulting from a large MCS moved out of northeast Oklahoma. This vortex persisted through the afternoon of 11 June, during which severe convection fired in and near the MCV circulation as it moved into the lower Ohio Valley. In addition, the event occurred during BAMEX, or bow echo and mesoscale convective vortex experiment, which provided a relatively dense collection of upper air observations during the intensification period of this vortex. Given the anomalously strong and long-lived nature of the circulation and the dense data set, this MCV is of particular interest to the objectives of this study. The first part of this study explores MCV processes through deterministic forecasting via the WRF model as well as detailed analyses of observations. Many of the theories put forth by past literature are tested as well. Using both 10 and 4-km resolutions, 36-hour WRF forecasts have been run from 00 UTC on 10, 11 and 12 June, covering the entire lifecycle of the MCV and its parent MCS. Another important objective is to evaluate the WRF’s ability to predict the secondary convection produced by the MCV on 11 June. This is particularly important since convection in and near an existing MCV circulation can have significant feedback effects on the strength and longevity of the MCV. Additionally, the differences between the 10-km and 4-km runs are examined such that the importance of model resolution in MCV forecasting is determined. For the second part of this study, 20 ensemble forecasts have been run to derive probabilistic evaluations of MCV dynamics. Since an MCV event includes many feedback processes, determining error covariance between different variables is of significant importance in understanding the lifecycle of a long-lived MCV event. Error covariance of several dynamic variables and processes is evaluated in this study, including the initial shortwave, the parent MCS of 10 June, midlevel temperature/latent heating, atmospheric stability, ambient wind shear, vertical displacement, the strength of the surface cold pool, and the timing, location and strength of the secondary convection.
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