One of the most common mesoscale organizational modes of deep convection is the squall line. However, the cloud-scale organizational mode within the convective region of squall lines demonstrates great variability. Specifically, the structure of the convective region may often be described within a spectrum ranging from discrete cells at one end of the spectrum to a continuous slab-like overturning at the other. In order to gain insight into why lines exhibit such different internal structures, a study was undertaken to see if there are notable differences between the inflow environments of the two ends of the organizational spectrum.

Lines of convection occurring in 2001-2002 over the contiguous United States were classified based upon radar reflectivity into "cell", "slab" and "undetermined" categories. Radiosonde reports in proximity to the lines were collected and composited for both the cell and slab types, subject to constraints on the representativeness of the soundings.

Substantial differences in both the kinematic and the thermodynamic properties of the composite soundings were found for the cell and slab cases. "Slab" cases tend to have much stronger low-level shear of both the line-parallel and line-perpendicular wind components. In the line-parallel direction, the slab environment has a substantially higher wind magnitude throughout the sounding. The slab composite also exhibits maxima in both components of the wind below 1.5 km above ground level, in contrast to the cell composite which does not. Thermodynamic differences include greater CAPE, drier low levels and a higher lifting condensation level in the cell composite. An attempt to relate these differences in the environment to the observed differences in the internal organizational mode is presented.