Polar stratospheric temperatures are positively skewed, with a typical value of skewness of 0.64 in Northern Hemisphere winter, an asymmetry that determines the character of ozone climate coupling and stratosphere-troposphere interactions. This skewness is often attributed to the fact that temperatures are bounded from below by a radiative limit while dynamical wave-driven events like sudden stratospheric warmings can cause significantly larger positive anomalies. In this talk, I will examine the positive skewness of upward wave activity flux itself as a driver of the temperature distribution. I will use the ideas of linear interference to explain the positive skewness of upward wave activity flux. In particular, I will show that a nonlinear relationship between the two terms that make up the heat flux anomaly can be used to explain its positive skewness. Finally, by using a toy statistical model of wave interference in the lower stratosphere, and I will show that the westward tilt of the climatological wave is the key ingredient to obtaining a positively skewed upward wave activity flux distribution.