Multiply-nested mesoscale numerical simulations with horizontal resolution up to 3.3 km are performed to study the generation of mesoscale gravity waves from the lift cycle of idealized baroclinic jet-front systems. Long-lived vertically-propagating mesoscale scale gravity waves with horizontal wavelengths ~100-200 km are simulated originating from the exit region of the upper-tropospheric jet streak, in a manner consistent with past observational studies. Sensitivity experiments show that the characteristics of these mesoscale waves do not depend on the model resolution as long as they are sufficiently resolved. The residue of nonlinear balance equation is found to be a useful index in diagnosing flow imbalance and predicting the wave generation. Balanced adjustment, generalized from the classical geostrophic adjustment, is proposed to explain the initiation of these mesoscale gravity waves from the unbalanced upper-tropospheric jet-front systems.