Simplified T-REX soundings are used as the basis for a series of idealized, two-dimensional simulations of airflow over double bell-shaped topography with an elevated valley using the Naval Research Laboratory's Coupled Ocean-Atmopshere Mesoscale Prediction System (COAMPS). A two-layer stability profile (constant tropospheric and stratospheric values) and a three-layer wind speed profile (constant tropospheric shear, constant wind jet, and constant reverse shear) are used. In the initial set of dynamic simulations, westerly flow begins to reach the valley floor only when the wind speeds at both ridge top and in the upper-level jet maximum exceed 15 m/s and 50 m/s, respectively. Inversions near 5 km reduce the amount of penetration, while inversions near the ridge top result in a hydraulic-type subcritical to supercritical transition. When an idealized heating profile is applied to the steady state dynamic solutions, westerlies already near the valley floor can sweep across the entire valley within 3-4 hours. For more moderate upstream shears, sufficiently strong heating can result in penetration in approximately six hours, corresponding to an afternoon onset of westerlies. In weaker sheared cases, heating generates dramatic changes in the flow regime. These thresholds show good agreement with observations in many cases, but some cases do have later than predicted onsets.