By using parcel model theory to construct a two-dimensional parameter space formed by low-level atmospheric stability and moisture, a simple framework on which to examine certain fire parcel properties associated with vertical column development is established. This framework is used to investigate if the Haines Index has some skill at predicting wildfire severity, where wildfire severity is assumed to be directly connected to vertical column development and the result of significant fire parcel ascent. By modeling the ascent of a moist, entraining fire parcel in four different background states—a 3 km deep boundary layer, a 2 km deep boundary layer, a 3 km deep boundary layer topped by an inversion layer, and a 2 km deep boundary layer topped by an inversion layer—the study shows that parcel properties that describe ascent and vertical column development are most significant when the boundary layer temperature lapse rate is near adiabatic and lower-level atmospheric humidity is relatively high. A shallower instead of a deeper boundary layer lowers parcel ascent, and an upper-level inversion lowers parcel ascent even further. This study shows that entraining fire parcel properties and magnitudes associated with significant ascent do not necessarily correspond to a Haines Index for a potential for high fire severity. The results suggest that the Haines Index may need to be refined or reformed depending on the stability and humidity in the boundary layer and vertical structure of the atmosphere. This study is a start to understanding the influence of the background state on fire parcel convection and an attempt to explain how the Haines Index works from an elementary but physical point of view.