The Eastern United States Side-Door Cold Front of 22 April 1987: A Case
Study of an Intense Atmospheric Density Current
Gregory J. Hakim
Department of Atmospheric Science, State University of New York at
Albany, Albany, New York 12222
Monthly Weather Review, 120, 2738--2762. (1992)
A case study if presented of an unusual cold front that affected the east
coast of the United States on 22 April 1987. Noteworthy aspects of this
front are its genesis behind a preexisting back-door front, its propagation
to the southwest, the shallow nature of the cold air associated with it
(<600 m), and the absence of precipitation. This front has been termed
a "side-door" front because of the significant differences between it and
typical back-door fronts, such as its direction of propagation and vertical
structure. Weather conditions in the mid-Atlantic states changed abruptly
from partly cloudy skies, light winds, and 25-30C surface temperatures
ahead of the front to a windy (gusts to 20 m/s), low overcast regime with
temperatures 10-15C cooler behind the front.
Analysis of satellite imagery, surface data, and sounding data revealed
that the front possessed density-current structure during a portion of
its lifetime. Observed front-relative flow, as well as agreement between
computed and observed frontal velocity, support this conclusion. Results
from this study demonstrate that the cold front evolved without the blocking
and channeling effects of a major mountain range, as is typically the case
for similar events around the world. It is hypothesized that the front
formed in response to differential surface heating and friction along the
New England coast. Similarly, the differential heating across the coastline
contributed to the intensification of the front as well as to the evolution
of the density-current structure later in the life history of the front.
Results of this study relevant to several numerical simulations of similar
events are discussed.