Mission Summary 5/6


An early-morning MCS left a boundary over northern TX, extending southwestward to the Abilene area and the west to south of Lubbock. A dryline was forecast to move into West Texas during the day.
Warm, moist low-level air was leading to large amounts of CAPE near the old outflow boundary in N TX, but upper flow was weakening rapidly in that region. VORTEX targeted the dryline and local terrain features in west Texas for storm initiation. CAPE was rather small, but forecasted to increase throughout the day, as backing and increasing low-level flow brought higher-CAPE air northwestward into the region.
The dryline became quite sharp and retreated slowly late in the afternoon over the Caprock area. Cumulus was observed on the dryline for several hours, and a good initiation experiment was conducted with the NOAA P-3 and NCAR Electra, as well as mobile CLASS and mobile mesonet teams. The dryline failed to initiate convection. Our best guess for the reason is that the sounding was moist-neutral through the lowest 250 mB, and then CAPE increased above that level. We are guessing that the clouds which formed along the dryline entrained too much dry air between the LCL and the more favorably stratified air above 600 mB.
Events so far during VORTEX make it obvious that we have little or no useful knowledge about the processes of storm initiation and the processes that suppress initiation. The best we can do at this point is to make sure the environment would support supercells, guess whether or not the "lid" can be "broken", identify a boundary along which we expect convergence, and hope for the best. When in the field, we realize that the initiation of storms is a much more complicated process, depending to a large degree on events that occur on scales we don't routinely observe, on subtle features in the low-level stratification and shear structure, and for which we don't have routine, dependable numerical guidance.

Erik Rasmussen
Jerry Straka

Return to Case Study Page