At the surface, observations during the morning of the 27th (roughly 10 AM CDT) revealed a cold front arcing to the southwest from a surface low near Fayetteville, Arkansas, through the DFW Metroplex, and into the Permian Basin. This would later become an important feature, as thunderstorm updrafts continually regenerated southwestward along the front into the Texas Hill Country during the afternoon. At the same time, visible satellite imagery showed the location of two remnant outflow boundaries laid down by an overnight area of convection across the Piney Woods of East Texas and into southern Arkansas. The southern outflow boundary would later become a focus for thunderstorm initiation east of DFW. An additional, very subtle feature elucidated by visible satellite imagery, was a southwestward-propagating gravity wave, also spawned by the now-decayed overnight convective system, denoted by dashed yellow lines. The gravity wave and cold front all met up just north of Waco near a meso-low, which would eventually become the initiation point for the Jarrell supercell.
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Surface observations and analysis by the Hydrometeorological Prediction Center (HPC, now Weather Prediction Center) valid at 15Z, or 10 AM CDT (a), and visible satellite imagery valid at 11 AM CDT (b) showing the location of remnant outflow boundaries, and a southwestward-moving gravity wave near Waco.
