Case studies of convective initiations using dual-doppler analysis during the Convective and Orographically-induced Precipitation Study (COPS)

Two case studies have been developed using dual-Doppler analysis in southwestern Germany and eastern France during the Convective and Orographically-induced Precipitation Study (COPS). This study took place during the summer months of 2007 in the Vosges and Black Forest Mountains with the Rhine Valley in between. This region receives threats of severe thunderstorm activity leading to possible flash flood events in the populated valley. Currently the Qualitative Precipitation Forecast (QPF) skill in these low-mountain regions is inadequate. The goal of this campaign was to retrieve high quality data for improving numerical models in this region of complex terrain (Wulfmeyer et al. 2008).

A climatological study was previously conducted in order to first determine the distribution of Convection Initiation (CI) events in the study region, including their growth characteristics with time. Using the DWD German radar network, a statistical analysis was done during these months for 2000-2008 to determine any favorable genesis zones in this region. Given 3190 total events identified over the 9-year period, results showed that the density of CI events were twice as great over the mountains than over the valley (Weckwerth et al. 2011).

Cases of CI in the mountains and the valley were then explored in order to provide detailed information on the mechanisms leading to CI in each area. On 06 August 2007, initiation developed in the Vosges Mountains at 1400 UTC which later intensified and produced an outflow boundary over the valley where more CI occurred. This cell formed ahead of an approaching rainband in a region of leeside convergence as observed in the dual-Doppler wind fields. The water vapor field created using tomography showed high enough values in the pre-convective environment to fuel the storm for the rapid intensification seen. The case of 13 August 2007 involved continuous CI starting at 0830 UTC in a particular genesis zone located in the valley. Due to the lack of dual-Doppler overlap, the pre-convective winds were unable to be determined. However, syntheses were created for later times to observe the mechanisms for CI evolution. The syntheses reveal northerly low level winds providing inflow into the southwesterly propagating storms. When compared to water vapor, values were unfavorably low in the northern Rhine at the genesis location. Results for the 13 August case contain gaps for identifying mechanisms leading to CI formation. The Weather Research and Forecasting Model (WRF) will also be run in order to enhance the understanding of the events for these two cases and especially help fill gaps for the 13 August case.