Wednesday, 25 January 2012: 9:15 AM
Analysis of the N Alabama MCV on the Morning of 27 April 2011
Room 252/253 (New Orleans Convention Center )
Near 1000 UTC (5 am local time) on 27 April 2011 an expansive QLCS crossed into the state of Alabama. As a portion of the line crossed traversed Walker County, a prominent mesoscale convective vortex (MCV) became apparent from the NWS 88-D radars in Huntsville and Birmingham. The center of the entity crossed I-65 in Cullman County at about 1100 UTC. Over the next 1.5 h, the MCV remained a distinct feature in the larger scale convective line as it progressed through Marshall and Jackson Counties. Just after 1230 UTC, the MCV had crossed the extreme northeastern corner of Alabama and continued NE into extreme northwestern Georgia and southern Tennessee. At least about a dozen tornadoes occurred in association with this mesoscale circulation, including EF-2s that impacted the Hanceville area (Cullman County) and the Lake Guntersville State Park (Marshall County). While the day was forecast to have a high tornado threat, this early morning system caught many off guard as the worst weather wasn't expected until the afternoon and early evening (when multiple violent tornadoes did indeed scour the state). For about an hour of the MCV's time in northern Alabama, dual-Doppler sampling was accomplished by the Huntsville NWS 88-D (S-band) and UAHuntsville's Advanced Radar for Meteorological and Operational Research (ARMOR, C-band) radars. These radars are situated about 65 km apart along a NE-SW oriented baseline. This configuration allows for a true dual-Doppler analysis of the MCV, which will be completed to assess the presence of multiple vortices in the MCV area supported by initial radar inspection and early damage surveys conducted by the NWS. Dual-polarimetric observations from the ARMOR permit an investigation of hydrometeor distribution. Results of both analyses will presented and comparisons will be made to previously well documented MCVs, such as those observed during the BAMEX field campaign in 2003 (eg: David and Trier 2007).