During quiet conditions, thermospheric models show good statistical agreement with measured neutral densities. However when magnetic activity increases, there is significant discrepancy between both the magnitude of the change in neutral density and the timing of the change. In general the models underpredict the maximum density reached at altitudes between 350 and 500 km, and lag the temporal variations by up to 3 hours. Part of the discrepancy is due to use of ap, a 3-hour index which reflects geomagnetic activity. We show that by use of Dst, a magnetic storm index, we obtain better forecasts of neutral densities during storms and compare the predictions with observations and current models. The new equations, based on Dst, will be included in the new empirical model to be used at Air Force Space Command (AFSPC).