A common attribute of both aforementioned case studies was an upstream subsynoptic-scale upper-tropospheric potential vorticity (PV) anomaly over the southern Rockies. In the first case (24 May 2011), an early morning mesoscale PV anomaly located ahead of the upstream PV anomaly triggered disorganized morning convection over eastern Colorado and western Nebraska. As this convection moved eastward and better organized, it produced a southward-propagating outflow boundary that became the focus of new convection over Oklahoma where it intersected the dryline. This Oklahoma convection became severe as the aforementioned subsynoptic-scale PV anomaly reached the High Plains.
In the second case (19 June 2011), a mesoscale PV anomaly crossed the southern Rockies, intercepted a flow of moisture from the Gulf of Mexico, triggered mesoscale frontogenesis, warm-air advection, and ascent, and enabled mesoscale convective system (MCS) development to occur in moist upslope flow over southwestern Nebraska, northwestern Kansas, and northeastern Colorado. The resulting MCS produced two separate high-impact weather events: 1) a stratiform precipitation-dominated heavy rainstorm with embedded convective elements in southwestern Nebraska, and 2) a convection-dominated severe weather episode with isolated supercells to the east along the Nebraska-Kansas border. Neither event was anticipated nor forecast very well by the available operational models.