Deamplification of the upper ridge in the western U.S., evident as early as the morning of 29 December, resulted in less amplification of the eastern U.S. upper trough and associated northern stream upper low. Evolution of upstream and downstream upper features can have a significant impact on the amplification and deamplification of the primary system being diagnosed.
If movement of the upper low in satellite imagery suggests the center will not pass south of the forecast area, the chances of precipitation associated with the upper deformation zone (Bader et al. 1995) can be greatly reduced. Similar to event 1, the upper low tracked southeast into the Ohio Valley, but the center of the upper low in event 2 did not track as far south.
The upper impulse, associated with the upper jet streak, tracked quickly east through the Tennessee Valley and Carolinas. This limited the low-level thermal and moisture advection and convergence in the southeast and mid-Atlantic U.S.
The upper impulse that rotated around the southern semicircle of the upper low initiated the cyclogenesis over the interior southeastern U.S. Identification of upper impulses in satellite imagery is crucial, based on lessons from event 2.