A model of NO abundance in the lower thermosphere is described. The model includes time dependence, an energetic electron flux calculation that includes transport, neutral and ion photochemistry, and vertical diffusion. We show that a steady state calculation is inadequate for calculating NO abundance. We examine the relationship between observed NO abundance and the integrated energy input to the lower thermosphere over the previous day. It is shown that the relationship between the energy input and the NO abundance varies with the local time of the NO measurement and with the length of daylight. These dependencies arise due to the role of photodissociation as a loss mechanism for NO. This model is designed for analysis of NO observations and will be used in the analysis of observations by the SNOE spacecraft <Barth et al., 1999>.