Diagnosing Coupled Jet-Streak Circulations for a Northern Plains Snow Band
from the operational Nested-Grid Model
Gregory J. Hakim
Department of Atmospheric Science, State University of New York at
Albany, Albany, New York 12222
Louis W. Uccellini
Meteorological Operations Division, National Meteorological Center,
Camp Springs, Maryland 20746
Weather and Forecasting, 7, 26--48. (1992)
On 17 March 1988, moderate to heavy snow developed in a 100- to 200-km
wide band extending from South Dakota to northern Michigan. The 4- to 8-
inch snowfall within this band was not associated with major cyclogenesis,
and developed 500 to 600 km north of a stationary surface front. A diagnostic
analysis based on an application of the General Meteorological Package
(GEMPAK 5.0) to a numerical simulation from the operational nested-grid
model (NGM) is utilized to show that the development of this snow band
is related to the interaction of two upper-tropospheric jet-streaks and
their associated transverse circulation patterns. The eastward propagation
of a jet streak from the West Coast toward the middle United States and
to the south of a slower-moving jet along the U.S.-Canadian border led
to a merger of the ascent maxima associated with the direct and indirect
circulations of the northern and southern jets, respectively. The snow
band developed as the ascending branches of the jet-streak circulation
patterns merged, with the eastward propagation of the heaviest snow linked
to the motion of the coupled circulation pattern. The study also demonstrates
the usefulness of the operational NGM for providing the higher-resolution
datasets required to related the evolution of jet-streak circulation patterns
to the development of mesoscale precipitation bands.