ABSTRACT

	The frontal structure and occlusion process in a cyclone of
moderate intensity that affected the Central United States in January
1995 is examined.  The deep warm frontal zone associated with this 
cyclone had a lateral extension to the southwest of the sea-level pres-
sure minimum that, although characterized by cold air advection near the 
surface, had many of the characteristics of a warm front aloft.  In
fact, this feature closely resembled the bent-back frontal structures
previously documented only in association with explosively deepening mari-
time cyclones.

	The development of a warm occluded structure was investigated
with the aid of a numerical simulation of the event performed using the
University of Wisconsin-Nonhydrostatic Modeling System (UW-NMS).  The
development of the warm occluded structure was asynchronous in the
vertical; occuring first at middle tropospheric levels and later near
the surface, in contrast to the classical occlusion process.  Near the
surface, the warm occluded front was formed as the warm front was over-
taken by the frontogenetically inactive portion of the historical cold
frontal zone.  At middle tropospheric levels, the warm occluded struc-
ture formed as a result of the cold frontal zone approaching, and 
subsequently ascending, the warm frontal zone, in accord with the 
classical occlusion mechanism.

	The observed asynchronous evolution of the occluded structure
is proposed to result from the vertical variation in vortex strength
associated with the upper-level potential vorticity (PV) anomaly that
controls the cyclogenesis.  It is suggested that the occlusion process
begins aloft, where the associated vortex strength is greatest, and
gradually penetrates downward toward the surface during the cyclone life
cycle.  Additionally, a characteristic "treble clef" shape to the upper-
level PV anomaly is shown to be a sufficient condition for asserting the
presence of a warm occluded structure in the underlying troposphere.